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Sample records for acid catalytic activity

  1. Bacterial lipopolysaccharide suppresses the production of catalytically active lysosomal acid hydrolases in human macrophages

    PubMed Central

    1986-01-01

    Sub-microgram quantities of bacterial lipopolysaccharide (LPS) have been found to substantially reduce the intracellular catalytic activities of three representative lysosomal enzymes (namely, acid phosphatase, hexosaminidase, and beta-glucuronidase) in human monocyte- derived macrophages. This response was not associated with a concurrent increase in enzyme catalytic activity in the culture supernatant, and hence, could not be explained by mobilization of preformed material. By conducting experiments in the presence and absence of indomethacin, a cyclooxygenase inhibitor, the reduction in lysosomal enzyme catalytic activities was shown not to be dependent on the ability of LPS to induce prostaglandin E2 production. The response was not found to be the result of a more generalized LPS-dependent reduction in the ability of the cells to synthesize protein, since the presence of LPS in macrophage cultures did not appreciably affect the amount of [35S]methionine incorporated into total cellular proteins. A kinetic analysis of the effect of LPS on the down-regulation of enzyme catalytic activities indicated that this was an early response of the cells to LPS exposure. An investigation of the effects of blockade of enzyme catabolism (using the lysosomotropic weak-base, methylamine) indicated that the reduction of catalytic enzyme activities in response to LPS was probably due to a decreased rate of production of active product, rather than an enhanced rate of enzyme catabolism. This suggestion was confirmed by experiments in which the synthesis of pro- hexosaminidase (measured by biosynthetic labeling with [35S]methionine and specific immunoprecipitation of labeled pro-hexosaminidase) was found to be reduced by 42% after a 24-h exposure to LPS (although the synthesis of complement component C3 was stimulated by a factor of 4.5). It is suggested that the ability of LPS to regulate the functional expression of protein products contributes to changes in the overall

  2. 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

  3. Mutation in aspartic acid residues modifies catalytic and haemolytic activities of Bacillus cereus sphingomyelinase.

    PubMed Central

    Tamura, H; Tameishi, K; Yamada, A; Tomita, M; Matsuo, Y; Nishikawa, K; Ikezawa, H

    1995-01-01

    Four aspartic acid residues (Asp126, Asp156, Asp233 and Asp295) of Bacillus cereus sphingomyelinase (SMase) in the conservative regions were changed to glycine by in vitro mutagenesis, and the mutant SMases [D126G (Asp126-->Gly etc.), D156G, D233G and D295G] were produced in Bacillus brevis 47, a protein-producing strain. The sphingomyelin (SM)-hydrolysing activity of D295G was completely abolished and those of D126G and D156G were reduced by more than 80%, whereas that of D233G was not so profoundly affected. Two mutant enzymes (D126G and D156G) were purified and characterized further. The hydrolytic activities of D126G and D156G toward four phosphocholine-containing substrates with different hydrophobicities, SM, 2-hexadecanoylamino-4-nitrophenylphosphocholine(HNP), lysophosphatidylcholine (lysoPC) and p-nitro-phenylphosphocholine (p-NPPC), were compared with those of the wild-type. The activity of D126G toward water-soluble p-NPPC was comparable with that of the wild-type. On the other hand, D156G catalysed the hydrolysis of hydrophilic substrates such as HNP and p-NPPC more efficiently (> 4-fold) than the wild-type. These results suggested that Asp126 and Asp156, located in the highly conserved region, may well be involved in a substrate recognition process rather than catalytic action. Haemolytic activities of the mutant enzymes were found to be parallel with their SM-hydrolysing activities. Two regions, including the C-terminal region containing Asp295, were found to show considerable sequence identity with the corresponding regions of bovine pancreatic DNase I. Structural predictions indicated structural similarity between SMase and DNase I. An evolutionary relationship based on the catalytic function was suggested between the structures of these two phosphodiesterases. Images Figure 2 Figure 3 Figure 4 Figure 6 PMID:7639690

  4. 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.

  5. Characterization of ferromagnetic sludge-based activated carbon and its application in catalytic ozonation of p-chlorobenzoic acid.

    PubMed

    Lu, Siying; Liu, Yongze; Feng, Li; Sun, Zhongen; Zhang, Liqiu

    2017-03-09

    In order to solve the separation problem of powdered sludge-based activated carbon (SAC), a series of novel ferromagnetic sludge-based activated carbons (FMSACs, with different iron content 2.3, 4.3, and 9.5 wt%) with a good magnetic separation ability were prepared through co-precipitation method in this study. The structure and physicochemical properties of FMSACs and their catalytic ozonation performance on the removal of p-chlorobenzoic acid (p-CBA) were investigated. The saturation magnetization (Ms) of FMSACs was determined in the range of 0.3674-5.7992 emu g(-1), and experiments confirmed that these FMSACs could be easily separated by magnetic fields. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis indicated that magnetite and maghemite were the main magnetic phases in FMSACs. Comparing with ozonation alone and SAC catalytic ozonation, the presence of 2.3 wt% - FMSAC improved the degradation of p-CBA during catalytic ozonation from 44 and 70 to 80%. The tertiary butanol inhibition experiment indicated that FMSACs catalytic ozonation process followed hydroxyl radical reaction mechanism. Furthermore, after six repetitive catalytic ozonation runs, 2.3 wt% - FMSAC still showed relatively high catalytic activity for the removal of p-CBA. Consequently, the novel FMSACs with magnetic separation ability and catalytic performance provide a practical pathway for the sludge utilization.

  6. 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.

  7. 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

  8. Secretion and N-linked glycosylation are required for prostatic acid phosphatase catalytic and antinociceptive activity.

    PubMed

    Hurt, Julie K; Fitzpatrick, Brendan J; Norris-Drouin, Jacqueline; Zylka, Mark J

    2012-01-01

    Secretory human prostatic acid phosphatase (hPAP) is glycosylated at three asparagine residues (N62, N188, N301) and has potent antinociceptive effects when administered to mice. Currently, it is unknown if these N-linked residues are required for hPAP protein stability and activity in vitro or in animal models of chronic pain. Here, we expressed wild-type hPAP and a series of Asn to Gln point mutations in the yeast Pichia pastoris X33 then analyzed protein levels and enzyme activity in cell lysates and in conditioned media. Pichia secreted wild-type recombinant (r)-hPAP into the media (6-7 mg protein/L). This protein was as active as native hPAP in biochemical assays and in mouse models of inflammatory pain and neuropathic pain. In contrast, the N62Q and N188Q single mutants and the N62Q, N188Q double mutant were expressed at lower levels and were less active than wild-type r-hPAP. The purified N62Q, N188Q double mutant protein was also 1.9 fold less active in vivo. The N301Q mutant was not expressed, suggesting a critical role for this residue in protein stability. To explicitly test the importance of secretion, a construct lacking the signal peptide of hPAP was expressed in Pichia and assayed. This "cellular" construct was not expressed at levels detectable by western blotting. Taken together, these data indicate that secretion and post-translational carbohydrate modifications are required for PAP protein stability and catalytic activity. Moreover, our findings indicate that recombinant hPAP can be produced in Pichia--a yeast strain that is used to generate biologics for therapeutic purposes.

  9. Restoration of catalytic activity beyond wild-type level in glucoamylase from Aspergillus awamori by oxidation of the Glu400-->Cys catalytic-base mutant to cysteinesulfinic acid.

    PubMed

    Fierobe, H P; Mirgorodskaya, E; McGuire, K A; Roepstorff, P; Svensson, B; Clarke, A J

    1998-03-17

    Glucoamylase catalyzes the hydrolysis of glucosidic bonds with inversion of the anomeric configuration. Site-directed mutagenesis and three-dimensional structure determination of the glucoamylase from Aspergillus awamori previously identified Glu179 and Glu400 as the general acid and base catalyst, respectively. The average distance between the two carboxyl groups was measured to be 9.2 A, which is typical for inverting glycosyl hydrolases. In the present study, this distance was increased by replacing the catalytic base Glu400 with cysteine which was then oxidized to cysteinesulfinic acid. Initially, this oxidation occurred during attempts to carboxyalkylate the Cys400 residue with iodoacetic acid, 3-iodopropionic acid, or 4-bromobutyric acid. However, endoproteinase Lys-C digestion of modified glucoamylase followed by high-pressure liquid chromatography in combination with matrix-assisted laser desorption ionization/time-of-flight mass spectrometry on purified peptide fragments demonstrated that all enzyme derivatives contained the cysteinesulfinic acid oxidation product of Cys400. Subsequently, it was demonstrated that treatment of Glu400-->Cys glucoamylase with potassium iodide in the presence of bromine resulted in complete conversion to the cysteinesulfinic acid product. As expected, the catalytic base mutant Glu400-->Cys glucoamylase had very low activity, i.e., 0.2% compared to wild-type. The oxidation of Cys400 to cysteinesulfinic acid, however, restored activity (kcat) on alpha-1,4-linked substrates to levels up to 160% of the wild-type glucoamylase which corresponded to approximately a 700-fold increase in the kcat of the Glu400-->Cys mutant glucoamylase. Whereas Glu400-->Cys glucoamylase was much less thermostable and more sensitive to guanidinium chloride than the wild-type enzyme, the oxidation to cysteinesulfinic acid was accompanied by partial recovery of the stability.

  10. An isozyme of acid alpha-glucosidase with reduced catalytic activity for glycogen.

    PubMed Central

    Beratis, N G; LaBadie, G U; Hirschhorn, K

    1980-01-01

    Both the common and a variant isozyme of acid alpha-glucosidase have been purified from a heterozygous placenta with CM-Sephadex, ammonium sulfate precipitation, dialysis, Amicon filtration, affinity chromatography by Sephadex G-100, and DEAE-cellulose chromatography. Three and two activity peaks, from the common and variant isozymes, respectively, were obtained by DEAE-cellulose chromatography using a linear NaCl gradient. The three peaks of activity of the common isozyme were eluted with 0.08, 0.12, and 0.17 M NaCl, whereas the two peaks of the variant, with 0.01 and 0.06 M NaCl. The pH optimum and thermal denaturation at 57 degrees C were the same in all enzyme peaks of both isozymes. Rabbit antiacid alpha-glucosidase antibodies produced against the common isozyme were found to cross-react with both peaks of the variant isozyme. The two isozymes shared antigenic identity and had similar Km's with maltose as substrate. Normal substrate saturation kinetics were observed with the common isozyme when glycogen was the substrate, but the variant produced an S-shaped saturation curve indicating a phase of negative and positive cooperativity at low and high glycogen concentrations, respectively. The activity of the variant was only 8.6% and 19.2% of the common isozyme when assayed with nonsaturating and saturating concentrations of glycogen, respectively. A similar rate of hydrolysis of isomaltose by both isozymes was found indicating that the reduced catalytic activity of the variant isozyme toward glycogen is not the result of a reduced ability of this enzyme to cleave the alpha-1,6 linkages of glycogen. Images Fig. 2 Fig. 4 Fig. 6 PMID:6770674

  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. 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.

  13. 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

  14. p-Coumaric acid decarboxylase from Lactobacillus plantarum: structural insights into the active site and decarboxylation catalytic mechanism.

    PubMed

    Rodríguez, Héctor; Angulo, Iván; de Las Rivas, Blanca; Campillo, Nuria; Páez, Juan A; Muñoz, Rosario; Mancheño, José M

    2010-05-15

    p-Coumaric acid decarboxylases (PDCs) catalyze the nonoxidative decarboxylation of hydroxycinnamic acids to generate the corresponding vinyl derivatives. Despite the biotechnological relevance of PDCs in food industry, their catalytic mechanism remains largely unknown. Here, we report insights into the structural basis of catalysis for the homodimeric PDC from Lactobacillus plantarum (LpPDC). The global fold of LpPDC is based on a flattened beta-barrel surrounding an internal cavity. Crystallographic and functional analyses of single-point mutants of residues located within this cavity have permitted identifying a potential substrate-binding pocket and also to provide structural evidences for rearrangements of surface loops so that they can modulate the accessibility to the active site. Finally, combination of the structural and functional data with in silico results enables us to propose a two-step catalytic mechanism for decarboxylation of p-coumaric acid by PDCs where Glu71 is involved in proton transfer, and Tyr18 and Tyr20 are involved in the proper substrate orientation and in the release of the CO(2) product.

  15. Controlled synthesis of nanosized palladium icosahedra and their catalytic activity towards formic-acid oxidation.

    PubMed

    Lv, Tian; Wang, Yi; Choi, Sang-Il; Chi, Miaofang; Tao, Jing; Pan, Likun; Huang, Cheng Zhi; Zhu, Yimei; Xia, Younan

    2013-10-01

    Pd icosahedra with sizes controlled in the range of 5-35 nm were synthesized in high purity through a combination of polyol reduction and seed-mediated growth. The Pd icosahedra were obtained with purity >94 % and uniform sizes controlled in the range of 5-17 nm by using ethylene glycol as both the reductant and solvent. The studies indicate that the formation of Pd nanocrystals with an icosahedral shape was very sensitive to the reaction kinetics. The success of this synthesis relies on the use of HCl to manipulate the reaction kinetics and thus control the twin structure and shape of the resultant nanocrystals. The size of the Pd icosahedra could be further increased up to 35 nm by seed-mediated growth, with 17 nm Pd icosahedra serving as seeds. The multiply twinned Pd icosahedra could grow into larger sizes, and their shape and multiply twinned structure were preserved. Thanks to the presence of twin defects, the Pd icosahedra showed a catalytic current density towards formic-acid oxidation that was 1.9 and 11.6 times higher than that of single-crystal Pd octahedra, which were also fully covered by {111} facets, and commercial Pd/C, respectively.

  16. 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.

  17. Removal of aqueous oxalic acid by heterogeneous catalytic ozonation with MnOx/sewage sludge-derived activated carbon as catalysts.

    PubMed

    Huang, Yuanxing; Sun, Yaru; Xu, Zhihua; Luo, Mengyu; Zhu, Chunlei; Li, Liang

    2017-01-01

    MnOx/sewage sludge-derived activated carbon (MnOx/SAC) was prepared as catalysts to improve the performance of aqueous oxalic acid degradation by ozonation. The results indicated that MnOx/SAC had excellent catalytic activity in mineralization of oxalic acid during heterogeneous catalytic ozonation process. MnOx/SAC with a manganese load of 30% exhibited the strongest catalytic activity under the condition of solution pH3.5, which enhanced the oxalic acid removal from 10.3% to 92.2% in 60min compared with that treated by ozone alone. Increase of catalyst dosage and aqueous ozone concentration was advantageous for oxalic acid removal from water. On the basis of catalyst characterization analysis and the observation of inhibitory effect induced by higher pH, less catalyst dosage as well as the presence of hydroxyl radical scavenger, it was deduced that the reaction mechanism involved both hydroxyl radicals attack and surface reactions.

  18. Poly-alpha-glutamic acid synthesis using a novel catalytic activity of RimK from Escherichia coli K-12.

    PubMed

    Kino, Kuniki; Arai, Toshinobu; Arimura, Yasuhiro

    2011-03-01

    Poly-L-α-amino acids have various applications because of their biodegradable properties and biocompatibility. Microorganisms contain several enzymes that catalyze the polymerization of L-amino acids in an ATP-dependent manner, but the products from these reactions contain amide linkages at the side residues of amino acids: e.g., poly-γ-glutamic acid, poly-ε-lysine, and cyanophycin. In this study, we found a novel catalytic activity of RimK, a ribosomal protein S6-modifying enzyme derived from Escherichia coli K-12. This enzyme catalyzed poly-α-glutamic acid synthesis from unprotected L-glutamic acid (Glu) by hydrolyzing ATP to ADP and phosphate. RimK synthesized poly-α-glutamic acid of various lengths; matrix-assisted laser desorption ionization-time of flight-mass spectrometry showed that a 46-mer of Glu (maximum length) was synthesized at pH 9. Interestingly, the lengths of polymers changed with changing pH. RimK also exhibited 86% activity after incubation at 55°C for 15 min, thus showing thermal stability. Furthermore, peptide elongation seemed to be catalyzed at the C terminus in a stepwise manner. Although RimK showed strict substrate specificity toward Glu, it also used, to a small extent, other amino acids as C-terminal substrates and synthesized heteropeptides. In addition, RimK-catalyzed modification of ribosomal protein S6 was confirmed. The number of Glu residues added to the protein varied with pH and was largest at pH 9.5.

  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. Catalytic activity of thiacalix[4]arenetetrasulfonate metal complexes on modified anion-exchangers for ascorbic acid oxidation.

    PubMed

    Odo, Junichi; Hirashima, Tomomi; Hayashida, Tomoko; Miyauchi, Asuka; Minemoto, Mami; Iuchi, Masato; Inoguchi, Masahiko

    2013-01-01

    The catalysis of ascorbic acid (AsA) oxidation by anion-exchangers modified with metal complexes of thiacalix[4]arenetetrasulfonate (Me-TCAS[4]A-500, Me=Mn(3+), Fe(3+), Co(3+), Ce(4+), Cu(2+), Zn(2+), Ni(2+), and H2) were investigated. Me-TCAS[4]A-500 (Me=Mn(3+), Fe(3+), Ce(4+), and Cu(2+)) all exhibited the ability to catalyze the oxidative reaction of AsA to dehydroascorbic acid. However, in the presence of high concentrations of AsA, only Cu(2+)-TCAS[4]A-500 was capable of complete oxidation of the acid. Moreover, after six repeat uses, Cu(2+)-TCAS[4]A-500 maintained high and relatively constant catalytic activity. Prior treatment of glucose solutions with Cu(2+)-TCAS[4]A-500, even in the presence of high AsA concentrations, enabled the satisfactory determination of glucose without interference by AsA. Cu(2+)-TCAS[4]A-500 will therefore be applicable as an artificial substitute for ascorbate oxidase, and may be useful as a means to eliminate AsA interference during the analysis of vital compounds such as glucose and uric acid.

  1. Heterogeneous Fenton-like catalytic removal of p-nitrophenol in water using acid-activated fly ash.

    PubMed

    Zhang, Aili; Wang, Nannan; Zhou, Jiti; Jiang, Ping; Liu, Guangfei

    2012-01-30

    The use of nitric-acid-activated fly ash (AFA), as heterogeneous Fenton-like catalyst for p-nitrophenol (p-NP) removal from water, was investigated. The physicochemical characteristics of AFA were better than those of raw fly ash (RFA). Under experimental conditions of pH 1.5-5.1, H(2)O(2) dosage 83.3-333 mgL(-1), AFA loaded 5.0-20 gL(-1), and temperature 298-348 K, the p-NP removal rate increased with the increase of H(2)O(2) dosage, AFA loaded and temperature. The highest removal rate (98%) was observed at pH 2.0 when H(2)O(2) dosage 166.5 mgL(-1), AFA loaded 10 gL(-1) and temperature 298 K. However, good p-NP removal efficiency (98.8%) could still be achieved under milder pH (5.1) conditions when enough reaction time (14 h) was applied. The leached iron concentration increased with decrease in pH and with increase in reaction time. The homogenous catalysis caused by leached iron was negligible. The less reaction time and higher AFA load could be selected flexibly for catalytic stability and reusability in actual application. The probable heterogeneous catalytic mechanisms were proposed.

  2. 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).

  3. Nanoporous bimetallic Pt-Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid.

    PubMed

    Zhang, Zhonghua; Wang, Yan; Wang, Xiaoguang

    2011-04-01

    We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al(75)Pt(15)Au(10) precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al(75)Pt(15)Au(10) precursor is composed of a single-phase Al(2)(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt(60)Au(40) nanocomposites (np-Pt(60)Au(40) NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt(60)Au(40) NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt(60)Au(40) NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt(60)Au(40) NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acid fuel cells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.

  4. Severing of a hydrogen bond disrupts amino acid networks in the catalytically active state of the alpha subunit of tryptophan synthase

    PubMed Central

    Axe, Jennifer M; O'Rourke, Kathleen F; Kerstetter, Nicole E; Yezdimer, Eric M; Chan, Yan M; Chasin, Alexander; Boehr, David D

    2015-01-01

    Conformational changes in the β2α2 and β6α6 loops in the alpha subunit of tryptophan synthase (αTS) are important for enzyme catalysis and coordinating substrate channeling with the beta subunit (βTS). It was previously shown that disrupting the hydrogen bond interactions between these loops through the T183V substitution on the β6α6 loop decreases catalytic efficiency and impairs substrate channeling. Results presented here also indicate that the T183V substitution decreases catalytic efficiency in Escherchia coli αTS in the absence of the βTS subunit. Nuclear magnetic resonance (NMR) experiments indicate that the T183V substitution leads to local changes in the structural dynamics of the β2α2 and β6α6 loops. We have also used NMR chemical shift covariance analyses (CHESCA) to map amino acid networks in the presence and absence of the T183V substitution. Under conditions of active catalytic turnover, the T183V substitution disrupts long-range networks connecting the catalytic residue Glu49 to the αTS-βTS binding interface, which might be important in the coordination of catalytic activities in the tryptophan synthase complex. The approach that we have developed here will likely find general utility in understanding long-range impacts on protein structure and dynamics of amino acid substitutions generated through protein engineering and directed evolution approaches, and provide insight into disease and drug-resistance mutations. PMID:25377949

  5. Nanoporous bimetallic Pt-Au alloy nanocomposites with superior catalytic activity towards electro-oxidation of methanol and formic acid

    NASA Astrophysics Data System (ADS)

    Zhang, Zhonghua; Wang, Yan; Wang, Xiaoguang

    2011-04-01

    We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al75Pt15Au10 precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray (EDX) analysis. The Al75Pt15Au10 precursor is composed of a single-phase Al2(Au,Pt) intermetallic compound, and can be fully dealloyed in a 20 wt.% NaOH or 5 wt.% HCl aqueous solution. The dealloying leads to the formation of the nanoporous Pt60Au40 nanocomposites (np-Pt60Au40 NCs) with an fcc structure. The morphology, size and crystal orientation of grains in the precursor can be conserved in the resultant nanoporous alloy. The np-Pt60Au40 NCs consist of two zones with distinct ligament/channel sizes and compositions. The formation mechanism of these np-Pt60Au40 NCs can be rationalized based upon surface diffusion of more noble elements and spinodal decomposition during dealloying. Electrochemical measurements demonstrate that the np-Pt60Au40 NCs show superior catalytic activity towards the electro-oxidation of methanol and formic acid in the acid media compared to the commercial JM-Pt/C catalyst. This material can find potential applications in catalysis related areas, such as direct methanol or formic acidfuelcells. Our findings demonstrate that dealloying is an effective and simple strategy to realize the alloying of immiscible systems under mild conditions, and to fabricate novel nanostructures with superior performance.We present a facile route to fabricate novel nanoporous bimetallic Pt-Au alloy nanocomposites by dealloying a rapidly solidified Al75Pt15Au10 precursor under free corrosion conditions. The microstructure of the precursor and the as-dealloyed sample was characterized using X-ray diffraction, scanning electron

  6. Strong counteranion effects on the catalytic activity of cationic silicon Lewis acids in Mukaiyama aldol and Diels-Alder reactions.

    PubMed

    Hara, Kenji; Akiyama, Ryuto; Sawamura, Masaya

    2005-12-08

    [chemical reaction: see text]. A toluene-coordinated silyl borate, [Et3Si(toluene)]B(C6F5)4, demonstrated catalytic activities significantly higher than those of Me3SiOTf and Me3SiNTf2 in Mukaiyama aldol and Diels-Alder reactions.

  7. 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

  8. 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.

  9. Identification of amino acid residues essential for catalytic activity of gentisate 1,2-dioxygenase from Pseudomonas alcaligenes NCIB 9867.

    PubMed

    Chua, C H; Feng, Y; Yeo, C C; Khoo, H E; Poh, C L

    2001-10-16

    Gentisate 1,2-dioxygenase (GDO, EC 1.13.11.4) is a ring cleavage enzyme that utilizes gentisate as a substrate yielding maleylpyruvate as the ring fission product. Mutant GDOs were generated by both random mutagenesis and site-directed mutagenesis of the gene cloned from Pseudomonas alcaligenes NCIB 9867. Alignment of known GDO sequences indicated the presence of a conserved central core region. Mutations generated within this central core resulted in the complete loss of enzyme activity whereas mutations in the flanking regions yielded GDOs with enzyme activities that were reduced by up to 78%. Site-directed mutagenesis was also performed on a pair of highly conserved HRH and HXH motifs found within this core region. Conversion of these His residues to Asp resulted in the complete loss of catalytic activity. Mutagenesis within the core region could have affected quaternary structure formation as well as cofactor binding. A mutant enzyme with increased catalytic activities was also characterized.

  10. 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.

  11. Heterogeneous catalytic degradation of phenolic substrates: catalysts activity.

    PubMed

    Liotta, L F; Gruttadauria, M; Di Carlo, G; Perrini, G; Librando, V

    2009-03-15

    This review article explored the catalytic degradation of phenol and some phenols derivates by means of advanced oxidation processes (AOPs). Among them, only the heterogeneous catalyzed processes based on catalytic wet peroxide oxidation, catalytic ozonation and catalytic wet oxidation were reviewed. Also selected recent examples about heterogeneous photocatalytic AOPs will be presented. In details, the present review contains: (i) data concerning catalytic wet peroxide oxidation of phenolic compounds over metal-exchanged zeolites, hydrotalcites, metal-exchanged clays and resins. (ii) Use of cobalt-based catalysts, hydrotalcite-like compounds, active carbons in the catalytic ozonation process. (iii) Activity of transition metal oxides, active carbons and supported noble metals catalysts in the catalytic wet oxidation of phenol and acetic acid. The most relevant results in terms of catalytic activity for each class of catalysts were reported.

  12. 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.

  13. Improvement of catalytic activity of Candida rugosa lipase in the presence of calix[4]arene bearing iminodicarboxylic/phosphonic acid complexes modified iron oxide nanoparticles.

    PubMed

    Ozyilmaz, Elif; Bayrakci, Mevlut; Yilmaz, Mustafa

    2016-04-01

    In the present study, iron oxide magnetite nanoparticles, prepared through a co-precipitation method, were coated with phosphonic acid or iminodicarboxylic acid derivatives of calix[4]arene to modulate their surfaces with different acidic groups. Candida rugosa lipase was then directly immobilized onto the modified nanoparticles through sol-gel encapsulation. The catalytic activities and enantioselectivities of the two encapsulated lipases in the hydrolysis reaction of (R/S)-naproxen methyl ester and (R/S)-2-phenoxypropionic acid methyl ester were assessed. The results showed that the activity and enantioselectivity of the lipase were improved when the lipase was encapsulated in the presence of calixarene-based additives; the encapsulated lipase with the phosphonic acid derivative of calix[4]arene had an excellent rate of enantioselectivity against the (R/S)-naproxen methyl and (R/S)-2-phenoxypropionic acid methyl esters, with E=350 and 246, respectively, compared to the free enzyme. The encapsulated lipases (Fe-Calix-N(COOH)) and (Fe-Calix-P) showed good loading ability and little loss of enzyme activity, and the stability of the catalyst was very good; they only lost 6-11% of the enzyme's activity after five batches.

  14. 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

  15. 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.

  16. 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.

  17. Microwave assisted catalytic wet air oxidation of H-acid in aqueous solution under the atmospheric pressure using activated carbon as catalyst.

    PubMed

    Zhang, Yaobin; Quan, Xie; Chen, Shuo; Zhao, Yazhi; Yang, Fenglin

    2006-09-01

    Catalytic wet air oxidation (CWAO) is a promising method for the treatment of heavily contaminated wastewater. However, its application is restricted due to severe operation conditions (high pressure and high temperature). A microwave (MW) assisted oxidation method was investigated aiming to treat heavily contaminated wastewater under milder conditions. H-acid (1-amino-8-naphthol-3, 6-disulfonic acid) was selected as target compound to evaluate the performance of this novel process. The removal of H-acid and TOC (total organic carbon) for H-acid solution of 3000 mg/L reached as high as 92.6% in 20 min and 84.2% in 60 min, respectively under optimal conditions. The existence of activated carbon and oxygen proved to be critical for effective treatment. The activated carbon acted not only as a catalyst for H-acid decomposition, but also as a special material for the absorption of MW energy. Air was supplied to the reactor as an oxygen source at constant flows. The amino group in H-acid was converted ultimately into nitrate, and sulfonic group into sulfate. This observation gave an evidence of H-acid mineralization although other organic intermediates were unable to be determined. The value of BOD(5)/COD (ratio of 5d biochemical oxygen demand to chemical oxygen demand) increased from 0.008 to 0.467 indicating a significant improvement of biodegradability for the solution, which is beneficial for the further biological treatment of the wastewater.

  18. Acid-base bifunctional catalytic surfaces for nucleophilic addition reactions.

    PubMed

    Motokura, Ken; Tada, Mizuki; Iwasawa, Yasuhiro

    2008-09-01

    This article illustrates the modification of oxide surfaces with organic amine functional groups to create acid-base bifunctional catalysts, summarizing our previous reports and also presenting new data. Immobilization of organic amines as bases on inorganic solid-acid surfaces afforded highly active acid-base bifunctional catalysts, which enabled various organic transformations including C--C coupling reactions, though these reactions did not proceed with either the homogeneous amine precursors or the acidic supports alone. Spectroscopic characterization, such as by solid-state MAS NMR and FTIR, revealed not only the interactions between acidic and basic sites but also bifunctional catalytic reaction mechanisms.

  19. 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.

  20. Effect of gamma irradiation on the texture, acidity and catalytic activity of silica-aluminium and silica-magnesia catalysts

    NASA Astrophysics Data System (ADS)

    Youssef, A. M.; Samra, S. E.; Ahmed, Awad I.

    The textural properties of non-irradiated and γ-irradiated silica-aluminium and silica-magnesia catalysts were determined from nitrogen adsorption. The acidities of these catalysts were measured by the chemisorption of pyridine. Cracking of cumene and dehydration of isopropanol were investigated on non-irradiated and γ-irradiated catalysts. Irradiation with γ-rays enhanced sintering, i.e. decreased the surface area and increased pore size. For silica-magnesia, γ-irradiation enhanced crystallization of Forsterite and Enstatite. The surface acidity decreased upon γ-irradiation and consequently the activity of the catalysts towards cracking of cumene and dehydration of isopropanol was reduced. The former reaction is structure-sensitive, while the latter is structure-insensitive.

  1. Green synthesis of gold and silver nanoparticles using gallic acid: catalytic activity and conversion yield toward the 4-nitrophenol reduction reaction

    NASA Astrophysics Data System (ADS)

    Park, Jisu; Cha, Song-Hyun; Cho, Seonho; Park, Youmie

    2016-06-01

    In the present report, gallic acid was used as both a reducing and stabilizing agent to synthesize gold and silver nanoparticles. The synthesized gold and silver nanoparticles exhibited characteristic surface plasmon resonance bands at 536 and 392 nm, respectively. Nanoparticles that were approximately spherical in shape were observed in high-resolution transmission electron microscopy and atomic force microscopy images. The hydrodynamic radius was determined to be 54.4 nm for gold nanoparticles and 33.7 nm for silver nanoparticles in aqueous medium. X-ray diffraction analyses confirmed that the synthesized nanoparticles possessed a face-centered cubic structure. FT-IR spectra demonstrated that the carboxylic acid functional groups of gallic acid contributed to the electrostatic binding onto the surface of the nanoparticles. Zeta potential values of -41.98 mV for the gold nanoparticles and -53.47 mV for the silver nanoparticles indicated that the synthesized nanoparticles possess excellent stability. On-the-shelf stability for 4 weeks also confirmed that the synthesized nanoparticles were quite stable without significant changes in their UV-visible spectra. The synthesized nanoparticles exhibited catalytic activity toward the reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. The rate constant of the silver nanoparticles was higher than that of the gold nanoparticles in the catalytic reaction. Furthermore, the conversion yield (%) of 4-nitrophenol to 4-aminophenol was determined using reversed-phase high-performance liquid chromatography with UV detection at 254 nm. The silver nanoparticles exhibited an excellent conversion yield (96.7-99.9 %), suggesting that the synthesized silver nanoparticles are highly efficient catalysts for the 4-nitrophenol reduction reaction.

  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. Thermal and electrochemical C-X activation (X = Cl, Br, I) by the strong Lewis acid Pd3(dppm)3(CO)2+ cluster and its catalytic applications.

    PubMed

    Lemaître, Frédéric; Lucas, Dominique; Groison, Katherine; Richard, Philippe; Mugnier, Yves; Harvey, Pierre D

    2003-05-07

    The stoichiometric and catalytic activations of alkyl halides and acid chlorides by the unsatured Pd(3)(dppm)(3)(CO)(2+) cluster (Pd(3)(2+)) are investigated in detail. A series of alkyl halides (R-X; R = t-Bu, Et, Pr, Bu, allyl; X = Cl, Br, I) react slowly with Pd(3)(2+) to form the corresponding Pd(3)(X)(+) adduct and "R(+)". This activation can proceed much faster if it is electrochemically induced via the formation of the paramagnetic species Pd(3)(+). The latter is the first confidently identified paramagnetic Pd cluster. The kinetic constants extracted from the evolution of the UV-vis spectra for the thermal activation, as well as the amount of electricity to bring the activation to completion for the electrochemically induced reactions, correlate the relative C-X bond strength and the steric factors. The highly reactive "R(+)" species has been trapped using phenol to afford the corresponding ether. On the other hand, the acid chlorides react rapidly with Pd(3)(2+) where no induction is necessary. The analysis of the cyclic voltammograms (CV) establishes that a dissociative mechanism operates (RCOCl --> RCO(+) + Cl(-); R = t-Bu, Ph) prior to Cl(-) scavenging by the Pd(3)(2+) species. For the other acid chlorides (R = n-C(6)H(13), Me(2)CH, Et, Me, Pr), a second associative process (Pd(3)(2+) + RCOCl --> Pd(3)(2+.....)Cl(CO)(R)) is seen. Addition of Cu(NCMe)(4)(+) or Ag(+) leads to the abstraction of Cl(-) from Pd(3)(Cl)(+) to form Pd(3)(2+) and the insoluble MCl materials (M = Cu, Ag) allowing to regenerate the starting unsaturated cluster, where the precipitation of MX drives the reaction. By using a copper anode, the quasi-quantitative catalytic generation of the acylium ion ("RCO(+)") operates cleanly and rapidly. The trapping of "RCO(+)" with PF(6)(-) or BF(4)(-) leads to the corresponding acid fluorides and, with an alcohol (R'OH), to the corresponding ester catalytically, under mild conditions. Attempts were made to trap the key intermediates "Pd(3)(Cl

  4. Catalytic reduction of 4-nitrophenol with gold nanoparticles synthesized by caffeic acid.

    PubMed

    Seo, Yu Seon; Ahn, Eun-Young; Park, Jisu; Kim, Tae Yoon; Hong, Jee Eun; Kim, Kyeongsoon; Park, Yohan; Park, Youmie

    2017-12-01

    In this study, various concentrations of caffeic acid (CA) were used to synthesize gold nanoparticles (CA-AuNPs) in order to evaluate their catalytic activity in the 4-nitrophenol reduction reaction. To facilitate catalytic activity, caffeic acid was removed by centrifugation after synthesizing CA-AuNPs. The catalytic activity of CA-AuNPs was compared with that of centrifuged CA-AuNPs (cf-CA-AuNPs). Notably, cf-CA-AuNPs exhibited up to 6.41-fold higher catalytic activity compared with CA-AuNPs. The catalytic activity was dependent on the caffeic acid concentration, and the lowest concentration (0.08 mM) produced CA-AuNPs with the highest catalytic activity. The catalytic activities of both CA-AuNPs and cf-CA-AuNPs decreased with increasing caffeic acid concentration. Furthermore, a conversion yield of 4-nitrophenol to 4-aminophenol in the reaction mixture was determined to be 99.8% using reverse-phase high-performance liquid chromatography. The product, 4-aminophenol, was purified from the reaction mixture, and its structure was confirmed by (1)H-NMR. It can be concluded that the removal of the reducing agent, caffeic acid in the present study, significantly enhanced the catalytic activity of CA-AuNPs in the 4-nitrophenol reduction reaction.

  5. Catalytic reduction of 4-nitrophenol with gold nanoparticles synthesized by caffeic acid

    NASA Astrophysics Data System (ADS)

    Seo, Yu Seon; Ahn, Eun-Young; Park, Jisu; Kim, Tae Yoon; Hong, Jee Eun; Kim, Kyeongsoon; Park, Yohan; Park, Youmie

    2017-01-01

    In this study, various concentrations of caffeic acid (CA) were used to synthesize gold nanoparticles (CA-AuNPs) in order to evaluate their catalytic activity in the 4-nitrophenol reduction reaction. To facilitate catalytic activity, caffeic acid was removed by centrifugation after synthesizing CA-AuNPs. The catalytic activity of CA-AuNPs was compared with that of centrifuged CA-AuNPs ( cf-CA-AuNPs). Notably, cf-CA-AuNPs exhibited up to 6.41-fold higher catalytic activity compared with CA-AuNPs. The catalytic activity was dependent on the caffeic acid concentration, and the lowest concentration (0.08 mM) produced CA-AuNPs with the highest catalytic activity. The catalytic activities of both CA-AuNPs and cf-CA-AuNPs decreased with increasing caffeic acid concentration. Furthermore, a conversion yield of 4-nitrophenol to 4-aminophenol in the reaction mixture was determined to be 99.8% using reverse-phase high-performance liquid chromatography. The product, 4-aminophenol, was purified from the reaction mixture, and its structure was confirmed by 1H-NMR. It can be concluded that the removal of the reducing agent, caffeic acid in the present study, significantly enhanced the catalytic activity of CA-AuNPs in the 4-nitrophenol reduction reaction.

  6. Enantioselective Michael additions of nitromethane by a catalytic double activation method using chiral lewis Acid and achiral amine catalysts.

    PubMed

    Itoh, Kennosuke; Kanemasa, Shuji

    2002-11-13

    Reactions of nitromethane with 1-(2-alkenoyl)-3,5-dimethylpyrazoles can be effectively catalyzed by R,R-DBFOX/Ph.Ni(ClO4)2.3H2O and achiral amine bases, each in a catalytic loading of 10 mol %, to give 1-(3-substituted 4-nitrobutanoyl)-3,5-dimethylpyrazoles in high chemical yields. Excellent enantioselectivities up to 98% ee have been achieved. The nitro moiety can be easily reduced on Raney nickel at atmospheric pressure, followed by concurrent cyclization, to give enantiomers of 4-substituted 2-pyrrolidinone derivatives after usual workup. This method can be successfully applied to a short step synthesis of (R)-(-)-rolipram.

  7. 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.

  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

    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.

  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 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

  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 Activation of Nitrogen Dioxide for Selective Synthesis of Nitroorganics

    DTIC Science & Technology

    2015-01-15

    AFRL-OSR-VA-TR-2015-0035 Catalytic activation of nitrogen dioxide for selective synthesis SETH BROWN UNIVERSITY OF NOTRE DAME DU LAC Final Report 01...8-98) v Prescribed by ANSI Std. Z39.18 12-01-2015 Final 15 Aug 2011 - 14 Aug 2014 Catalytic activation of nitrogen dioxide for selective synthesis...reductive elimination of the nitroarene has not. Nitrogen dioxide can be used as a source of the nitro group in reactions with arylboronic acids or their

  13. Reductive behaviour of acid azo dye based wastewater: Biocatalyst activity in conjunction with enzymatic and bio-electro catalytic evaluation.

    PubMed

    Sreelatha, S; Nagendranatha Reddy, C; Velvizhi, G; Venkata Mohan, S

    2015-01-01

    Present study illustrates the significance of biocatalyst's reductive behaviour in the degradation of dye molecules using glucose as co-substrate. An anaerobic system was operated at a dye concentration of 50mg/l with an organic loading rate (OLR) of 1.36 kg COD/m(3)-day. Decolourization and COD removal efficiencies were observed to be 42% and 48% respectively. Azo reductase (18.9 U) and dehydrogenase enzyme (1.4 μg/ml) activities showed increment with operation time. Anaerobic microenvironment showed dye reduction converting them into aromatic amines. The presence of mediators viz., cytochromes, quinines and Fe-S proteins depicted in the cyclic voltammetry profiles played a crucial role in transfer of electrons for the reduction of dye molecules. Bio-electro kinetic profiles obtained through Tafel analysis showed persistent reduction behaviour, which is in good correlation with dye degradation in the anaerobic microenvironment.

  14. Studies on the catalytic mechanism of pig purple acid phosphatase.

    PubMed

    Wynne, C J; Hamilton, S E; Dionysius, D A; Beck, J L; de Jersey, J

    1995-05-10

    Several independent experiments failed to reveal any evidence in support of the involvement of a phosphoryl-enzyme intermediate in the catalytic mechanism of pig allantoic fluid purple acid phosphatase: (i) attempts to label enzyme with phosphate derived from [32P]p-nitrophenyl phosphate were unsuccessful; (ii) values of kcat for a series of phosphate derivative varied over a wide range, with the enzyme showing a marked preference for activated ester and anhydride substrates over those with a stable leaving group; (iii) burst titrations revealed a "burst" of p-nitrophenol from p-nitrophenyl phosphate only when the enzyme was added after the substrate, suggesting that this result was an artifact of the order of addition of reagents; (iv) transphosphorylation from p-nitrophenyl phosphate to acceptor alcohols could not be detected, even under conditions where a transphosphorylation to hydrolysis ratio as low as 0.015 could have been measured; (v) enzyme-catalyzed exchange of 180 between phosphate and water was demonstrated, although at a rate much slower than that observed for other phosphatases where the involvement of a phosphoryl-enzyme intermediate in the mechanism has been clearly established. The present results are compared with those obtained in similar studies on other phosphatases, particularly the highly homologous beef spleen purple acid phosphatase, and their implications for the catalytic mechanism of the purple acid phosphatases are discussed.

  15. 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.

  16. 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.

  17. Anionic substitutes for catalytic aspartic acids in phosphoribulokinase.

    PubMed

    Runquist, Jennifer A; Miziorko, Henry M

    2002-09-15

    Mutagenic substitution of the invariant D42 and D169 residues in phosphoribulokinase (PRK) with amino acids that contain neutral side chains (e.g., alanine or asparagine) results in large decreases in catalytic efficiency (10(5)- and 10(4)-fold for replacement of D42 and D169, respectively). To further evaluate the importance of anionic side chains at residues 42 and 169, substitutions of glutamic acid (D42E, D169E) and cysteine (D42C and D169C in an otherwise cysteine-free protein) have been engineered. All purified mutant enzymes bind the fluorescent alternative substrate trinitrophenyl-ATP and the allosteric effector NADH similarly to wild-type PRK. For D42E and D42C, V(max) exhibits substantial decreases of 135- and 220-fold, respectively. Comparable substitutions for D169 result in smaller effects; D169E and D169C exhibit decreases in V(max) of 39- and 26-fold, respectively. Thus, regardless of the type of substitution, changes at D42 more profoundly affect catalytic rate than do comparable changes at D169. Precedent with enzymes in which cysteine replaces an acidic residue suggests that oxidation of the thiolate to a sulfinate can convert low-activity cysteine mutants into enzymes with improved activity. Periodate oxidation of cysteine-free PRK results in a slight decrease in activity. In contrast, comparable treatment of D42C and D169C proteins increases activity by 5- and 7-fold, respectively. Thus, for reasonably efficient catalysis, PRK requires anionic character in the side chains of residues 42 and 169. The enzyme can, however, tolerate substantial structural and chemical variability at these residues.

  18. [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.

  19. The roles of active-site residues in the catalytic mechanism of trans-3-chloroacrylic acid dehalogenase: a kinetic, NMR, and mutational analysis.

    PubMed

    Azurmendi, Hugo F; Wang, Susan C; Massiah, Michael A; Poelarends, Gerrit J; Whitman, Christian P; Mildvan, Albert S

    2004-04-13

    trans-3-Chloroacrylic acid dehalogenase (CaaD) converts trans-3-chloroacrylic acid to malonate semialdehyde by the addition of H(2)O to the C-2, C-3 double bond, followed by the loss of HCl from the C-3 position. Sequence similarity between CaaD, an (alphabeta)(3) heterohexamer (molecular weight 47,547), and 4-oxalocrotonate tautomerase (4-OT), an (alpha)(6) homohexamer, distinguishes CaaD from those hydrolytic dehalogenases that form alkyl-enzyme intermediates. The recently solved X-ray structure of CaaD demonstrates that betaPro-1 (i.e., Pro-1 of the beta subunit), alphaArg-8, alphaArg-11, and alphaGlu-52 are at or near the active site, and the >or=10(3.4)-fold decreases in k(cat) on mutating these residues implicate them as mechanistically important. The effect of pH on k(cat)/K(m) indicates a catalytic base with a pK(a) of 7.6 and an acid with a pK(a) of 9.2. NMR titration of (15)N-labeled wild-type CaaD yielded pK(a) values of 9.3 and 11.1 for the N-terminal prolines, while the fully active but unstable alphaP1A mutant showed a pK(a) of 9.7 (for the betaPro-1), implicating betaPro-1 as the acid catalyst, which may protonate C-2 of the substrate. These results provide the first evidence for an amino-terminal proline, conserved in all known tautomerase superfamily members, functioning as a general acid, rather than as a general base as in 4-OT. Hence, a reasonable candidate for the general base in CaaD is the active site residue alphaGlu-52. CaaD has 10 arginine residues, six in the alpha-subunit (Arg-8, Arg-11, Arg-17, Arg-25, Arg-35, and Arg-43), and four in the beta-subunit (Arg-15, Arg-21, Arg-55, and Arg-65). (1)H-(15)N-heteronuclear single quantum coherence (HSQC) spectra of CaaD showed seven to nine Arg-NepsilonH resonances (denoted R(A) to R(I)) depending on the protein concentration and pH. One of these signals (R(D)) disappeared in the spectrum of the largely inactive alphaR11A mutant (deltaH = 7.11 ppm, deltaN = 89.5 ppm), and another one (R

  20. The catalytic and photocatalytic activity of coal fly ashes

    NASA Astrophysics Data System (ADS)

    Dlugi, Ralph; Güsten, Hans

    Great differences in the catalytic and photocatalytic activity of two samples of fly ash from two different coal-fired power plants have been demonstrated to exist for two reactions of environmental significance, namely, the heterogeneous SO 2 oxidation in a smog chamber and the photochemical degradation of two polynuclear aromatic hydrocarbons adsorbed onto the fly ashes. At a relative humidity (r.h.) of 80%, the reaction rate for the heterogeneous SO 2 oxidation on an acidic fly ash (pH 5.65) is ten times higher than for the oxidation on a fly ash of pH 9.3. Compared to silica gel, the 'acidic' fly ash gives rise to a faster photocatalytic degradation of anthracene and phenanthrene, while the same aromatic hydrocarbons are highly resistant to photodegradation when adsorbed on the fly ash of pH 9.3. Possible explanations and environmental consequences of the differing catalytic activity of fly ashes are discussed.

  1. 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)

  2. 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.

  3. Method to produce catalytically active nanocomposite coatings

    DOEpatents

    Erdemir, Ali; Eryilmaz, Osman Levent; Urgen, Mustafa; Kazmanli, Kursat

    2016-02-09

    A nanocomposite coating and method of making and using the coating. The nanocomposite coating is disposed on a base material, such as a metal or ceramic; and the nanocomposite consists essentially of a matrix of an alloy selected from the group of Cu, Ni, Pd, Pt and Re which are catalytically active for cracking of carbon bonds in oils and greases and a grain structure selected from the group of borides, carbides and nitrides.

  4. 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.

  5. Hydrothermal catalytic deoxygenation of palmitic acid over nickel catalyst

    SciTech Connect

    Miao, Chao; Marin-Flores, Oscar; Davidson, Stephen D.; Li, Tingting; Dong, Tao; Gao, Difeng; Wang, Yong; Garcia-Pérez, Manuel; Chen, Shulin

    2016-02-01

    Fatty acid has recently received considerable interest as a possible precursor for producing renewable hydrocarbon. In this study, we investigated hydrothermal catalytic deoxygenation of palmitic acid to produce paraffin over a Ni/ZrO2 catalyst with no or low-pressure (100 psi) external supply of H2. The results show that the presence of water greatly improved conversion of palmitic acid and paraffin yield. Significant improvement was attributed to the formation of in-situ H2. Without an external H2 supply, a 64.2 C% conversion of palmitic acid was achieved in the presence of water, while only a 17.2 C% conversion was achieved without water. The results also show that the presence of water suppressed the side reactions of palmitic acid, specifically ketonization and esterification. We concluded that, compared with decarboxylation and hydrodeoxygenation, decarbonylation was the major route for palmitic acid deoxygenation catalyzed by Ni/ZrO2. Varieties of shorter-chain paraffin (C8–C14) were formed through hydrogenolysis, which also produced a considerable amount of CH4. A viable reaction pathway for hydrothermal catalytic deoxygenation of palmitic acid in the presence of Ni/ZrO2 was suggested. The results show that hydrogenolysis and decarbonylation were the major reactions that occurred. This study demonstrates that this hydrothermal catalytic process is a promising approach for producing liquid paraffin (C8–C15) from fatty acids under no or low-pressure H2.

  6. Catalytically Active Regenerative Sorbent beds (CARS) for airborne contaminants.

    PubMed

    Akse, J R; Thompson, J O

    1995-01-01

    The Pd on Al2O3 catalyst used in the projected Space Station's Trace Contaminant Control System (TCCS) catalytic oxidizer can be poisoned by volatile halogen-, sulfur-, and nitrogen-containing organic species. Catalytically Active Regenerable Sorbents (CARS) eliminate these problematic contaminants and the large carbon bed used for their elimination in a three-step process. Contaminants are conventionally adsorbed by the CARS bed. After saturation, the bed is connected to an off-line recirculation loop, filled with hydrogen, and then heated. At temperature, contaminants are hydrogenated on catalytic sites within the bed, forming simple alkanes and acid gases that are efficiently converted to innocuous salts in an in-line alkaline bed. The CARS bed is regenerated by this cycle and alkane gases are released to be safely oxidized in the catalytic oxidizer. A challenge mixture containing Freon-113, thiophene, trichloroethylene, Halon-1301, and dichloromethane at 1670, 75, 81, 68, and 83 mg/m3 was successfully treated using this technology, demonstrating the CARS feasibility.

  7. Metal-ion mutagenesis: conversion of a purple acid phosphatase from sweet potato to a neutral phosphatase with the formation of an unprecedented catalytically competent Mn(II)Mn(II) active site.

    PubMed

    Mitić, Natasa; Noble, Christopher J; Gahan, Lawrence R; Hanson, Graeme R; Schenk, Gerhard

    2009-06-17

    The currently accepted paradigm is that the purple acid phosphatases (PAPs) require a heterovalent, dinuclear metal-ion center for catalysis. It is believed that this is an essential feature for these enzymes in order for them to operate under acidic conditions. A PAP from sweet potato is unusual in that it appears to have a specific requirement for manganese, forming a unique Fe(III)-mu-(O)-Mn(II) center under catalytically optimal conditions (Schenk et al. Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 273). Herein, we demonstrate, with detailed electron paramagnetic resonance (EPR) spectroscopic and kinetic studies, that in this enzyme the chromophoric Fe(III) can be replaced by Mn(II), forming a catalytically active, unprecedented antiferromagnetically coupled homodivalent Mn(II)-mu-(H)OH-mu-carboxylato-Mn(II) center in a PAP. However, although the enzyme is still active, it no longer functions as an acid phosphatase, having optimal activity at neutral pH. Thus, PAPs may have evolved from distantly related divalent dinuclear metallohydrolases that operate under pH neutral conditions by stabilization of a trivalent-divalent metal-ion core. The present Mn(II)-Mn(II) system models these distant relatives, and the results herein make a significant contribution to our understanding of the role of the chromophoric metal ion as an activator of the nucleophile. In addition, the detailed analysis of strain broadened EPR spectra from exchange-coupled dinuclear Mn(II)-Mn(II) centers described herein provides the basis for the full interpretation of the EPR spectra from other dinuclear Mn metalloenzymes.

  8. Reaction kinetics of waste sulfuric acid using H2O2 catalytic oxidation.

    PubMed

    Wang, Jiade; Hong, Binxun; Tong, Xinyang; Qiu, Shufeng

    2016-12-01

    The process of recovering waste sulfuric acids using H2O2 catalytic oxidation is studied in this paper. Activated carbon was used as catalyst. Main operating parameters, such as temperature, feed rate of H2O2, and catalyst dosage, have effects on the removal of impurities from waste sulfuric acids. The reaction kinetics of H2O2 catalytic oxidation on impurities are discussed. At a temperature of 90°C, H2O2 feeding rate of 50 g (kg waste acid)(-1) per hour, and catalyst dosage of 0.2 wt% (waste acid weight), the removal efficiencies of COD and chrominance were both more than 99%, the recovery ratio of sulfuric acid was more than 95%, and the utilization ratio of H2O2 was 88.57%.

  9. Catalytic kinetic spectrophotometry for the determination of trace amount of oxalic acid in biological samples with oxalic acid-rhodamine B-potassium dichromate system

    NASA Astrophysics Data System (ADS)

    Zhai, Qing-Zhou; Zhang, Xiao-Xia; Liu, Qing-Zhou

    2006-09-01

    A new catalytic kinetic spectrophotometric method was proposed for determining trace oxalic acid based on the catalytic effect of oxalate on the oxidation of potassium dichromate with rhodamin B in 0.10 M of sulfuric acid. Good linearity is obtained over the concentration range 0.40-6.0 μg/mL of oxalic acid. After the reactions of the catalytic and non-catalytic systems were terminated by using 2.00 mL of 4 M sodium hydroxide solution, they can be stable for 3 h at room temperature. The apparent activation energy of the catalytic reaction is 12.44 kJ/mol. The effect of 50 coexisting substances was observed. The method was used to determine trace oxalic acid in tea, spinach and urine samples with satisfactory results.

  10. Catalytic kinetic spectrophotometry for the determination of trace amount of oxalic acid in biological samples with oxalic acid-rhodamine B-potassium dichromate system.

    PubMed

    Zhai, Qing-Zhou; Zhang, Xiao-Xia; Liu, Qing-Zhou

    2006-09-01

    A new catalytic kinetic spectrophotometric method was proposed for determining trace oxalic acid based on the catalytic effect of oxalate on the oxidation of potassium dichromate with rhodamin B in 0.10 M of sulfuric acid. Good linearity is obtained over the concentration range 0.40-6.0 microg/mL of oxalic acid. After the reactions of the catalytic and non-catalytic systems were terminated by using 2.00 mL of 4 M sodium hydroxide solution, they can be stable for 3 h at room temperature. The apparent activation energy of the catalytic reaction is 12.44 kJ/mol. The effect of 50 coexisting substances was observed. The method was used to determine trace oxalic acid in tea, spinach and urine samples with satisfactory results.

  11. Expression, purification, and characterization of a biologically active bovine enterokinase catalytic subunit in Escherichia coli.

    PubMed

    Yuan, Liu-Di; Hua, Zi-Chun

    2002-07-01

    Enterokinase (EC 3.4.21.9) is a serine proteinase in the duodenum that exhibits specificity for the sequence (Asp)(4)-Lys. It converts trypsinogen to trypsin. Its high specificity for the recognition site makes enterokinase (EK) a useful tool for in vitro cleavage of fusion proteins. cDNA encoding the catalytic chain of Chinese bovine enterokinase was cloned and its encoding amino acid sequence is identical to the previously reported sequence although there are two one-base mutations which do not change the encoded amino acid. The EK catalytic subunit cDNA was cloned into plasmid pET32a, and fused downstream to the fusion partner thioredoxin (Trx) and the following DDDDK enterokinase recognition sequence. The recombinant bovine enterokinase catalytic subunit was expressed in Escherichia coli BL21(DE3), and most products existed in soluble form. After an in vivo autocatalytic cleavage of the recombinant Trx-EK catalytic domain fusion protein, intact, biologically active EK catalytic subunit was released from the fusion protein. The recombinant intact EK catalytic subunit was purified to homogeneity with a specific activity of 720 AUs/mg protein through ammonium sulfate precipitation, DEAE chromatography, and gel filtration. The purified intact EK catalytic subunit has a K(m) of 0.17 mM, and K(cat) is 20.8s(-1). From 100 ml flask culture, 4.3 mg pure active EK catalytic subunits were obtained.

  12. 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.

  13. 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.

  14. Facile template-free synthesis of pine needle-like Pd micro/nano-leaves and their associated electro-catalytic activities toward oxidation of formic acid

    PubMed Central

    2011-01-01

    Pine needle-like Pd micro/nano-leaves have been synthesized by a facile, template-free electrochemical method. As-synthesized Pd micro/nano-leaves were directly electrodeposited on an indium tin oxide substrate in the presence of 1.0 mM H2PdCl4 + 0.33 M H3PO4. The formation processes of Pd micro/nano-leaves were revealed by scanning electron microscope, and further characterized by X-ray diffraction and electrochemical analysis. Compared to conventional Pd nanoparticles, as-prepared Pd micro/nano-leaves exhibit superior electrocatalytic activities for the formic acid oxidation. PMID:21711919

  15. Modification of ferrierite through post-synthesis treatments. Acidic and catalytic properties

    NASA Astrophysics Data System (ADS)

    Brylewska, Kamila; Tarach, Karolina A.; Mozgawa, Włodzimierz; Olejniczak, Zbigniew; Filek, Urszula; Góra-Marek, Kinga

    2016-12-01

    The main emphasis of this work was placed on a detailed characterization of structural, textural and acidic properties of FER zeolites with different Si/Al ratios in terms of their activity in ethanol dehydration reaction. Subsequent dealumination and desilication procedures were found to be an efficient methods of a secondary system of mesopore generation in the ferrierite crystals with preservation of their microporous characteristics. Through ethanol dehydration both the acidic and the textural features have a significant influence on catalytic performance of hierarchical ferrierites. It was shown that higher catalytic activity and selectivity to ethylene is ensured by zeolites with highly preserved microporous characteristic, i.e. well-developed micropore area and intrinsic acidity.

  16. Vitamin K epoxide reductase: homology, active site and catalytic mechanism.

    PubMed

    Goodstadt, Leo; Ponting, Chris P

    2004-06-01

    Vitamin K epoxide reductase (VKOR) recycles reduced vitamin K, which is used subsequently as a co-factor in the gamma-carboxylation of glutamic acid residues in blood coagulation enzymes. VKORC1, a subunit of the VKOR complex, has recently been shown to possess this activity. Here, we show that VKORC1 is a member of a large family of predicted enzymes that are present in vertebrates, Drosophila, plants, bacteria and archaea. Four cysteine residues and one residue, which is either serine or threonine, are identified as likely active-site residues. In some plant and bacterial homologues the VKORC1 homologous domain is fused with domains of the thioredoxin family of oxidoreductases. These might reduce disulfide bonds of VKORC1-like enzymes as a prerequisite for their catalytic activities.

  17. Catalytic ozonation of fenofibric acid over alumina-supported manganese oxide.

    PubMed

    Rosal, Roberto; Gonzalo, María S; Rodríguez, Antonio; García-Calvo, Eloy

    2010-11-15

    The catalytic ozonation of fenofibric acid was studied using activated alumina and alumina-supported manganese oxide in a semicontinuous reactor. The rate constants at 20°C for the non-catalytic reaction of fenofibric acid with ozone and hydroxyl radicals were 3.43±0.20 M(-1) s(-1) and (6.55±0.33)×10(9) M(-1) s(-1), respectively. The kinetic constant for the catalytic reaction between fenofibric acid and hydroxyl radicals did not differ significantly from that of homogeneous ozonation, either using Al(2)O(3) or MnO(x)/Al(2)O(3). The results showed a considerable increase in the generation of hydroxyl radicals due to the use of catalysts even in the case of catalytic runs performed using a real wastewater matrix. Both catalysts promoted the decomposition of ozone in homogeneous phase, but the higher production of hydroxyl radicals corresponded to the catalyst with more activity in terms of ozone decomposition. We did not find evidence of the catalysts having any effect on rate constants, which suggests that the reaction may not involve the adsorption of organics on catalyst surface.

  18. 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.

  19. Catalytic biodiesel production mediated by amino acid-based protic salts.

    PubMed

    Li, Jingbo; Guo, Zheng

    2017-02-06

    Hetero-/homo-geneous acid catalysts are effective catalysts for biodiesel produced from oils containing high free fatty acids. The protic salts synthesized from natural amino acids were examined for their catalytic activity and efficiency for esterification of oleic acid after structural identification and characterization. The melting points of the protic salts were measured. In the esterification reaction of oleic acid with methanol, [Asp][NO3] performed the best, correlating to its higher Hammett acidity. The optimal reaction conditions for esterification of oleic acid to achieve 97% biodiesel yield were: temperature 70 °C, catalyst 10% (w/w, on oleic acid basis), methanol to oleic acid ratio 7.5:1, and 5 h. [Asp][NO3] could be a generally good catalyst for esterification of oleic acid with alcohols with chain length up to 6. The biodiesel yield of 93.86% was obtained from palm fatty acid distillate, implying potential industrial application of the catalyst. Kinetic study indicated that the reaction followed a pseudo-first order reaction, with activation energy and pre-exponential of 57.36 kJ/mol and 44.24×105 min-1. In conclusion, the aspartic acid derived protic salt is a promising, operational simply, sustainable, renewable, and possible biodegradable catalyst for converting high content of free fatty acids into biodiesel.

  20. 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.

  1. 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.

  2. 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)

  3. Evidence that the catalytic activity of prokaryote leader peptidase depends upon the operation of a serine-lysine catalytic dyad.

    PubMed Central

    Black, M T

    1993-01-01

    Leader peptidase (LP) is the enzyme responsible for proteolytic cleavage of the amino acid leader sequence from bacterial preproteins. Recent data indicate that LP may be an unusual serine proteinase which operates without involvement of a histidine residue (M. T. Black, J. G. R. Munn, and A. E. Allsop, Biochem. J. 282:539-543, 1992; M. Sung and R. E. Dalbey, J. Biol. Chem. 267:13154-13159, 1992) and that, therefore, one or more alternative residues must perform the function of a catalytic base. With the aid of sequence alignments, site-specific mutagenesis of the gene encoding LP (lepB) from Escherichia coli has been employed to investigate the mechanism of action of the enzyme. Various mutant forms of plasmid-borne LP were tested for their abilities to complement the temperature-sensitive activity of LP in E. coli IT41. Data are presented which indicate that the only conserved amino acid residue possessing a side chain with the potential to ionize, and therefore with the potential to transfer protons, which cannot be substituted with a neutral side chain is lysine at position 145. The data suggest that the catalytic activity of LP is dependent on the operation of a serine-lysine catalytic dyad. Images PMID:8394311

  4. Catalytic ozonation of oxalic acid using carbon nanofibres on macrostructured supports.

    PubMed

    Restivo, J; Órfão, J J M; Pereira, M F R; Vanhaecke, E; Rönning, M; Iouranova, T; Kiwi-Minsker, L; Armenise, S; Garcia-Bordejé, E

    2012-01-01

    Carbon nanofibres (CNFs) were grown on different macrostructured supports such as cordierite monoliths, carbon felts and sintered metal fibres. The resulting composites exhibited excellent resistance to attrition/corrosion and its porosity is mainly due to mesoporous structures. The CNF/structured materials were tested in the ozonation of oxalic acid in a conventional semi-batch reactor after being crushed to powder form, and in a newly designed reactor that may operate in semi-batch or continuous operation. The CNFs supported on the different structured materials exhibited high catalytic activity in the mineralization of oxalic acid.

  5. Structure-based engineering of histidine residues in the catalytic domain of α-amylase from Bacillus subtilis for improved protein stability and catalytic efficiency under acidic conditions.

    PubMed

    Yang, Haiquan; Liu, Long; Shin, Hyun-dong; Chen, Rachel R; Li, Jianghua; Du, Guocheng; Chen, Jian

    2013-03-10

    This work aims to improve the protein stability and catalytic efficiency of α-amylase from Bacillus subtilis under acidic conditions by site-directed mutagenesis. Based on the analysis of a three dimensional structure model, four basic histidine (His) residues His(222), His(275), His(293), and His(310) in the catalytic domain were selected as the mutation sites and were further replaced with acidic aspartic acid (Asp), respectively, yielding four mutants H222D, H275D, H293D, H310D. The mutant H222D was inactive. Double and triple mutations were further conducted and four mutants H275/293D, H275/310D, H293/310D, and H275/293/310D were obtained. The acidic stability of enzyme was significantly enhanced after mutation, and 45-92% of initial activity of mutants was retained after incubation at pH 4.5 and 25°C for 24h, while that for wild-type was only 39.5%. At pH 4.5, the specific activity of wild-type and mutants H275D, H293D, H310D, H275/293D, H275/310D, H293/310D, and H275/293/310D were 108.2, 131.8, 138.9, 196.6, 156.3, 204.6, and 216.2U/mg, respectively. The catalytic efficiency for each active mutant was much higher than that of wild-type at low pH. The kcat/Km values of the mutants H275D, H293D, H310D, H275/293D, H275/310D, H293/310D, and H275/293/310D at pH 4.5 were 3.3-, 4.3-, 6.5-, 4.5-, 11.0-, 14.5-, and 16.7-fold higher, respectively, than that of the wild-type. As revealed by the structure models of the wild-type and mutant enzymes, the hydrogen bonds and salt bridges were increased after mutation, and an obvious shift of the basic limb toward acidity was observed for mutants. These changes around the catalytic domain contributed to the significantly improved protein stability and catalytic efficiency at low pH. This work provides an effective strategy to improve the catalytic activity and stability of α-amylase under acidic conditions, and the results obtained here may be useful for the improvement of acid-resistant ability of other enzymes.

  6. Catalytic conversion of inulin and fructose into 5-hydroxymethylfurfural by lignosulfonic acid in ionic liquids.

    PubMed

    Xie, Haibo; Zhao, Zongbao K; Wang, Qian

    2012-05-01

    In this work, we found that lignosulfonic acid (LS), which is a waste byproduct from the paper industry, in ionic liquids (ILs) can catalyze the dehydration of fructose and inulin into 5-hydroxymethylfurfural (HMF) efficiently, which is a promising potential substitute for petroleum-based building blocks. The effects of reaction time, temperature, catalyst loading, and reusability of the catalytic system were studied. It was found that a 94.3% yield of HMF could be achieved in only 10 min at 100 °C under mild conditions. The reusability study of the LS-IL catalytic system after removal of HMF by ethyl acetate extraction demonstrated that the catalytic activity decreased from 77.4 to 62.9% after five cycles and the catalytic activity could be recovered after simply removing the accumulated humins by filtration after adding ethanol to the LS-ILs. The integrated utilization of a biorenewable feedstock, catalyst, and ILs is an example of an ideal green chemical process.

  7. Manipulating catalytic pathways: deoxygenation of palmitic acid on multifunctional catalysts.

    PubMed

    Peng, Baoxiang; Zhao, Chen; Kasakov, Stanislav; Foraita, Sebastian; Lercher, Johannes A

    2013-04-08

    The mechanism of the catalytic reduction of palmitic acid to n-pentadecane at 260 °C in the presence of hydrogen over catalysts combining multiple functions has been explored. The reaction involves rate-determining reduction of the carboxylic group of palmitic acid to give hexadecanal, which is catalyzed either solely by Ni or synergistically by Ni and the ZrO2 support. The latter route involves adsorption of the carboxylic acid group at an oxygen vacancy of ZrO2 and abstraction of the α-H with elimination of O to produce the ketene, which is in turn hydrogenated to the aldehyde over Ni sites. The aldehyde is subsequently decarbonylated to n-pentadecane on Ni. The rate of deoxygenation of palmitic acid is higher on Ni/ZrO2 than that on Ni/SiO2 or Ni/Al2O3, but is slower than that on H-zeolite-supported Ni. As the partial pressure of H2 is decreased, the overall deoxygenation rate decreases. In the absence of H2, ketonization catalyzed by ZrO2 is the dominant reaction. Pd/C favors direct decarboxylation (-CO2), while Pt/C and Raney Ni catalyze the direct decarbonylation pathway (-CO). The rate of deoxygenation of palmitic acid (in units of mmol moltotal metal(-1) h(-1)) decreases in the sequence r(Pt black) ≈r(Pd black) >r(Raney Ni) in the absence of H2 . In situ IR spectroscopy unequivocally shows the presence of adsorbed ketene (C=C=O) on the surface of ZrO2 during the reaction with palmitic acid at 260 °C in the presence or absence of H2.

  8. 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.

  9. 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

  10. [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.

  11. Tannic acid functionalized graphene hydrogel for entrapping gold nanoparticles with high catalytic performance toward dye reduction.

    PubMed

    Luo, Jing; Zhang, Nan; Lai, Jianping; Liu, Ren; Liu, Xiaoya

    2015-12-30

    In this work, a simple, cost-effective, and environmental-friendly strategy was developed to synthesize gold nanoparticles (Au NPs) decorated graphene hydrogel with the use of tannic acid. This facile route involved the reduction of graphene oxide (GO) in the presence of tannic acid to form tannic acid functionalized graphene hydrogel, followed by loading and in situ reduction of AuCl4(-) ions in the graphene hydrogel network benefiting from the abundant phenol groups of tannic acid. Tannic acid (TA), a typical plant polyphenol widely present in woods, not only reduced GO and induced the self-assembly of reduced graphene oxide into graphene hydrogel, but also served as the reducing agent and stabilizer for the synthesis and immobilization of Au NPs, avoiding extra chemical reagent and any stabilizer. The obtained Au NPs decorated graphene hydrogel (Au@TA-GH) was fully characterized and exhibited much higher catalytic activities than the unsupported and other polymer-supported Au NPs toward the reduction of methylene blue (MB). In addition, the high catalytic activity of Au@TA-GH could withhold in different pH solution conditions. Another distinct advantage of Au@TA-GH as catalysts is that it can be easily recovered and reused for five cycles.

  12. Versatile Catalytic Hydrogenation Using A Simple Tin(IV) Lewis Acid

    PubMed Central

    Scott, Daniel J.; Phillips, Nicholas A.; Sapsford, Joshua S.; Deacy, Arron C.; Fuchter, Matthew J.

    2016-01-01

    Abstract Despite the rapid development of frustrated Lewis pair (FLP) chemistry over the last ten years, its application in catalytic hydrogenations remains dependent on a narrow family of structurally similar early main‐group Lewis acids (LAs), inevitably placing limitations on reactivity, sensitivity and substrate scope. Herein we describe the FLP‐mediated H2 activation and catalytic hydrogenation activity of the alternative LA iPr3SnOTf, which acts as a surrogate for the trialkylstannylium ion iPr3Sn+, and is rapidly and easily prepared from simple, inexpensive starting materials. This highly thermally robust LA is found to be competent in the hydrogenation of a number of different unsaturated functional groups (which is unique to date for main‐group FLP LAs not based on boron), and also displays a remarkable tolerance to moisture. PMID:27774711

  13. Human airway epithelia express catalytically active NEU3 sialidase.

    PubMed

    Lillehoj, Erik P; Hyun, Sang Won; Feng, Chiguang; Zhang, Lei; Liu, Anguo; Guang, Wei; Nguyen, Chinh; Sun, Wenji; Luzina, Irina G; Webb, Tonya J; Atamas, Sergei P; Passaniti, Antonino; Twaddell, William S; Puché, Adam C; Wang, Lai-Xi; Cross, Alan S; Goldblum, Simeon E

    2014-05-01

    Sialic acids on glycoconjugates play a pivotal role in many biological processes. In the airways, sialylated glycoproteins and glycolipids are strategically positioned on the plasma membranes of epithelia to regulate receptor-ligand, cell-cell, and host-pathogen interactions at the molecular level. We now demonstrate, for the first time, sialidase activity for ganglioside substrates in human airway epithelia. Of the four known mammalian sialidases, NEU3 has a substrate preference for gangliosides and is expressed at mRNA and protein levels at comparable abundance in epithelia derived from human trachea, bronchi, small airways, and alveoli. In small airway and alveolar epithelia, NEU3 protein was immunolocalized to the plasma membrane, cytosolic, and nuclear subcellular fractions. Small interfering RNA-induced silencing of NEU3 expression diminished sialidase activity for a ganglioside substrate by >70%. NEU3 immunostaining of intact human lung tissue could be localized to the superficial epithelia, including the ciliated brush border, as well as to nuclei. However, NEU3 was reduced in subepithelial tissues. These results indicate that human airway epithelia express catalytically active NEU3 sialidase.

  14. 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.

  15. Slow reactant-water exchange and high catalytic performance of water-tolerant Lewis acids.

    PubMed

    Koito, Yusuke; Nakajima, Kiyotaka; Kobayashi, Hisayoshi; Hasegawa, Ryota; Kitano, Masaaki; Hara, Michikazu

    2014-06-23

    (31)P nuclear magnetic resonance (NMR) spectroscopic measurement with trimethylphosphine oxide (TMPO) was applied to evaluate the Lewis acid catalysis of various metal triflates in water. The original (31)P NMR chemical shift and line width of TMPO is changed by the direct interaction of TMPO molecules with the Lewis acid sites of metal triflates. [Sc(OTf)3] and [In(OTf)3] had larger changes in (31)P chemical shift and line width by formation of the Lewis acid-TMPO complex than other metal triflates. It originates from the strong interaction between the Lewis acid and TMPO, which results in higher stability of [Sc(OTf)3TMPO] and [In(OTf)3TMPO] complexes than other metal triflate-TMPO complexes. The catalytic activities of [Sc(OTf)3] and [In(OTf)3] for Lewis acid-catalyzed reactions with carbonyl compounds in water were far superior to the other metal triflates, which indicates that the high stability of metal triflate-carbonyl compound complexes cause high catalytic performance for these reactions. Density functional theory (DFT) calculation suggests that low LUMO levels of [Sc(OTf)3] and [In(OTf)3] would be responsible for the formation of stable coordination intermediate with nucleophilic reactant in water.

  16. Cobalt triarylcorroles containing one, two or three nitro groups. Effect of NO₂ substitution on electrochemical properties and catalytic activity for reduction of molecular oxygen in acid media.

    PubMed

    Li, Bihong; Ou, Zhongping; Meng, Deying; Tang, Jijun; Fang, Yuanyuan; Liu, Rui; Kadish, Karl M

    2014-07-01

    Cobalt(III) triarylcorroles containing 0-3 nitro groups on the para-position of the three meso-phenyl rings of the macrocycle were synthesized and characterized by electrochemistry, mass spectrometry, (UV-vis) and (1)H NMR spectroscopy. The examined compounds are represented as (NO2Ph)(n)Ph(3-n)CorCo(PPh3), where n varies from 0 to 3 and Cor represents the core of the corrole. Each compound can undergo two metal-centered one-electron reductions leading to formation of Co(II) and Co(I) derivatives in CH2Cl2 or pyridine containing 0.1 M tetra-n-butylammonium perchlorate (TBAP). A stepwise two electron reduction of each NO2Ph group of the compound is also observed. The first is reversible and occurs in a single overlapping step at the same potential which involves an overall one-, two- or three-electron transfer process for compounds 2-4, respectively. This indicates the lack of an interaction between these redox active sites on the corroles. The second reduction of the NO2Ph groups is irreversible and located at a potential which overlaps the Co(II)/Co(I) process of the compounds. Thin-layer UV-visible spectroelectrochemical measurements in CH2Cl2, 0.1 M TBAP demonstrate the occurrence of an equilibrium between a Co(III) π-anion radical and a Co(II) derivative with an uncharged macrocycle after the first controlled potential reduction of the nitro-substituted corroles. All four cobalt corroles were also examined as catalysts for the electroreduction of O2 when coated on an edge-plane pyrrolytic graphite electrode in 1.0 M HClO4. This study indicates that the larger the number of nitro-substituents on the cobalt corrole, the better the compound acts as a catalyst.

  17. HIPK2 catalytic activity and subcellular localization are regulated by activation-loop Y354 autophosphorylation

    PubMed Central

    Siepi, Francesca; Gatti, Veronica; Camerini, Serena; Crescenzi, Marco; Soddu, Silvia

    2013-01-01

    HIPK2 (homeodomain-interacting protein kinase-2) binds to and phosphorylates, at Ser and Thr residues, a large number of targets involved in cell division and cell fate decision in response to different physiological or stress stimuli. Inactivation of HIPK2 has been observed in human and mouse cancers supporting its role as a tumor suppressor. Despite the biological relevance of this kinase, very little is known on how HIPK2 becomes catalytically active. Based on sequence homologies, HIPK2 has been taxonomically classified as a subfamily member of the dual-specificity tyrosine-regulated kinases (DYRKs) and the activation-loop Y354 of HIPK2 has been found phosphorylated in different cells; however, the relevance of this Y phosphorylation is presently unknown. Here, we show that HIPK2, which is extensively phosphorylated at S/T sites throughout its functional domains, becomes catalytically active by autophosphorylation at the activation-loop Y354. In particular, we found that, in analogy to DYRKs, HIPK2-Y354 phosphorylation is an autocatalytic event and its prevention, through Y354 substitution with non-phosphorylatable amino acids or by using the kinase inhibitor purvalanol A, induces a strong reduction of the HIPK2 S/T-kinase activity on different substrates. Interestingly, at variance from DYRKs, inhibition of HIPK2-Y354 phosphorylation induces a strong out-of-target Y-kinase activity in cis and a strong cytoplasmic relocalization of the kinase. Together, these results demonstrate that the catalytic activity, substrate specificity, and subcellular localization of HIPK2 are regulated by autophosphorylation of its activation-loop Y354. PMID:23485397

  18. 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.

  19. 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.

  20. 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.

  1. Amino acid residues adjacent to the catalytic cavity of tetramer L-asparaginase II contribute significantly to its catalytic efficiency and thermostability.

    PubMed

    Long, Shuiqing; Zhang, Xian; Rao, Zhiming; Chen, Kaiyue; Xu, Meijuan; Yang, Taowei; Yang, Shangtian

    2016-01-01

    L-Asparaginase (L-asparagine amidohydrolase, EC 3.5.1.1) catalyzes the hydrolysis of L-asparagine to L-aspartic acid and ammonia. It can be used to reduce the formation of acrylamide, which is carcinogenic to humans in foods, via removal of the precursor, asparagine, from the primary ingredients. However, low activity and poor thermostability of L-asparaginase restrict its application in food industry. In this study, we successfully improved thermostability and catalytic efficiency of L-asparaginase II (BsAII) from Bacillus subtilis B11-06 by site-directed mutagenesis. According to sequences alignment and homologous modeling, residues G107, T109 and S166 which were adjacent to the catalytic cavity were selected and substituted by Asp, Gln/Ser and Ala, respectively, to construct mutants G107D, T109Q, T109S and S166A. The BsAII mutant of G107D (G107Dansz) displayed superior performance in thermal tolerance and higher activity than the wild-type enzyme (towards L-asparagine). Comparative analysis of hydrogen bond interactions, surface electrostatic potential and structure of substrate binding pocket between G107Danszand BsAII indicated that the substitution of G107, which was adjacent to catalytic cavity with Asp, resulted in small conformational changes and surface electrostatic potential redistribution and contributed to the improved protein stability and catalytic efficiency.

  2. 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.

  3. Influence of sulphide Cu (I) promoting additives concentration on acid and catalytic properties of high-silica zeolites in straight-run gasoline conversion

    NASA Astrophysics Data System (ADS)

    Khomyakov, I. S.; Erofeev, V. I.; Kuok Khan, Fan

    2016-09-01

    In present article the influence of Cu2S promoting additives concentration on acid and catalytic properties of high silica MFI-type zeolites is investigated in the process of conversion of straight-run gasoline fractions of gas condensate into high octane components of motor fuels. It was shown that zeolite modified with 1% of Cu2S nanoscaled powder possesses the highest acid centers concentration and highest catalytic activity.

  4. [Catalytic stability in wet air oxidation of carboxylic acids over ZnFe0.25Al1.75 O4 catalyst].

    PubMed

    Xu, Ai-hua; Yang, Min; Du, Hong-zhang; Peng, Fu-yong; Sun, Cheng-lin

    2007-07-01

    Oxalic, formic and acetic acid are main intermediate products in catalytic wet air oxidation process (CWAO). The catalytic activity and stability in CWAO of the three short-chain organic acids over ZnFe0.25Al1.75O4 catalyst were studied. Oxalic acid is the only oxidizable intermediate and the largest amount of Fe leaching is 9.5 mg L(-1) at 160 degrees C during CWAO process. Formic and acetic acid have little influence on Fe leaching. Due to the strong reducible ability of oxalic acid, the amount of Fe leaching is larger in nitrogen atmosphere than that in oxygen atmosphere. Salicylic acid can be also degraded by ZnFe0.25Al1.75O4 catalyst with a high catalytic activity and stability.

  5. 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.

  6. 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

    2006-11-03

    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.

  7. 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.

  8. Isomorphous substitution and the generation of catalytic activity in VPI-5

    SciTech Connect

    Kraushaar-Czarnetzki, B.; Dogterom, R.J.; Stork, W.H.J.; Emeis, K.A.; Van Braam Houckgeest, J.P. ) )

    1993-05-01

    VPI-5 and substituted derivatives containing silicon or magnesium have been synthesized, analyzed, and tested for their catalytic activity. By means of [sup 29]Si solid-state NMR, it could be shown that SAPO-VPI-5 prepared with polyphosphoric acid as a phosphorus source exhibits both [open quotes]silica patches[close quotes] and isolated silicon atoms incorporated in the framework. Broensted acid sites in SAPO-and MAPO-VPI-5 could be detected by means of infrared spectroscopy in combination with pyridine adsorption. The isomorphously substituted VPI-5 samples were active in the hydroconversion of n-heptane, giving both cracking and isomerization products. The highest activity and the highest yield in iso-heptane, however, were observed with AlPO-VPI-5 as a catalyst. The catalytic activity could be ascribed to the presence of unreacted alumina. Upon treatment with an EDTA solution the Al/P atomic ratio decreased from 1.29 to 1.07, and the purified AlPO-VPI-5 showed considerably reduced catalytic activity. 28 refs., 6 figs., 2 tabs.

  9. Repositioning the catalytic triad aspartic acid of haloalkane dehalogenase: effects on stability, kinetics, and structure.

    PubMed

    Krooshof, G H; Kwant, E M; Damborský, J; Koca, J; Janssen, D B

    1997-08-05

    Haloalkane dehalogenase (DhlA) catalyzes the hydrolysis of haloalkanes via an alkyl-enzyme intermediate. The covalent intermediate, which is formed by nucleophilic substitution with Asp124, is hydrolyzed by a water molecule that is activated by His289. The role of Asp260, which is the third member of the catalytic triad, was studied by site-directed mutagenesis. Mutation of Asp260 to asparagine resulted in a catalytically inactive D260N mutant, which demonstrates that the triad acid Asp260 is essential for dehalogenase activity. Furthermore, Asp260 has an important structural role, since the D260N enzyme accumulated mainly in inclusion bodies during expression, and neither substrate nor product could bind in the active-site cavity. Activity for brominated substrates was restored to D260N by replacing Asn148 with an aspartic or glutamic acid. Both double mutants D260N+N148D and D260N+N148E had a 10-fold reduced kcat and 40-fold higher Km values for 1,2-dibromoethane compared to the wild-type enzyme. Pre-steady-state kinetic analysis of the D260N+N148E double mutant showed that the decrease in kcat was mainly caused by a 220-fold reduction of the rate of carbon-bromine bond cleavage and a 10-fold decrease in the rate of hydrolysis of the alkyl-enzyme intermediate. On the other hand, bromide was released 12-fold faster and via a different pathway than in the wild-type enzyme. Molecular modeling of the mutant showed that Glu148 indeed could take over the interaction with His289 and that there was a change in charge distribution in the tunnel region that connects the active site with the solvent. On the basis of primary structure similarity between DhlA and other alpha/beta-hydrolase fold dehalogenases, we propose that a conserved acidic residue at the equivalent position of Asn148 in DhlA is the third catalytic triad residue in the latter enzymes.

  10. 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.

  11. Computationally designed variants of Escherichia coli chorismate mutase show altered catalytic activity.

    PubMed

    Lassila, Jonathan Kyle; Keeffe, Jennifer R; Oelschlaeger, Peter; Mayo, Stephen L

    2005-04-01

    Computational protein design methods were used to predict five variants of monofunctional Escherichia coli chorismate mutase expected to maintain catalytic activity. The variants were tested experimentally and three active site mutants exhibited catalytic activity similar to or greater than the wild-type enzyme. One mutant, Ala32Ser, showed increased catalytic efficiency.

  12. Activity of catalytic silver nanoparticles modulated by capping agent hydrophobicity.

    PubMed

    Janani, Seralathan; Stevenson, Priscilla; Veerappan, Anbazhagan

    2014-05-01

    In this paper, a facile in situ method is reported for the preparation of catalytic silver nanoparticles (AgNPs) using N-acyl tyramine (NATA) with variable hydrophobic acyl length. Scanning electron microscopic analysis shows that NATA exists initially as larger aggregates in alkaline aqueous solution. The addition of AgNO3 dissociates these larger aggregate and subsequently promotes the formation of self-assembled NATA and AgNPs. Characterization of AgNPs using UV-vis spectroscopy, scanning electron microscope and transmission electron microscope revealed that the hydrophobic acyl chain length of NATA does not influence the particle size, shape and morphology. All NATA-AgNPs yielded relatively identical values in full width at half-maximum (FWHM) analysis, indicating that the AgNPs prepared with NATA are relatively polydispersed at all tested acyl chain lengths. These nanoparticles are able to efficiently catalyze the reduction of 4-nitro phenol to 4-amino phenol, 2-nitro aniline to 1,2-diamino benzene, 2,4,6-trinitro phenol to 2,4,6-triamino phenol by NaBH4 in an aqueous environment. The reduction reaction rate is determined to be pseudo-first order and the apparent rate constant is linearly dependent on the hydrophobic acyl chain length of the NATA. All reaction kinetics presented an induction period, which is dependent on the N-acyl chain length, indicating that the hydrophobic effects play a critical role in bringing the substrate to the metal nanoparticle surface to induce the catalytic reaction. In this study, however, the five catalytic systems have similar size and polydispersity, differing only in terms of capping agent hydrophobicity, and shows different catalytic activity with respect to the alkyl chain length of the capping agent. As discussed, the ability to modulate the metal nanoparticles catalytic property, by modifying the capping agent hydrophobicity represents a promising future for developing an efficient nanocatalyst without altering the size

  13. 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.

  14. Importance of ligand exchanges in Pd(II)-Brønsted acid cooperative catalytic approach to spirocyclic rings.

    PubMed

    Jindal, Garima; Sunoj, Raghavan B

    2014-11-12

    Increasing number of reports in the most recent literature convey the use of palladium and Brønsted acids as cooperative catalytic partners. However, the mechanistic understanding of several such cooperative catalytic reactions and the origin of cooperativity continue to remain limited. In transition metal catalysis, it is typically assumed that the native ligands, such as the acetates in palladium acetate, are retained throughout the catalytic cycle. Herein, we convey the significance of invoking ligand exchanges in transition metal catalysis by using the mechanism of a representative cooperative dual-catalytic reaction. Density functional theory (M06 and B3LYP) computations have been employed to decipher the mechanism of Pd(II)-Brønsted acid catalyzed migratory ring expansion reaction of an indenyl cyclobutanol to a spirocyclic indene bearing a quaternary carbon. The molecular role of water, benzoquinone and phosphoric acid has been probed by computing the energetics using several combinations of all these as ligands on palladium. Of the two key mechanistic possibilities examined, a Wacker-type pathway (involving a semipinacol ring expansion of cyclobutanol followed by a reductive elimination) is found to be energetically more preferred over an allylic pathway wherein the ring expansion in a Pd-π-allyl intermediate occurs subsequent to the initial allylic C-H activation. The Gibbs free energies of the transition states with the native palladium acetate are much higher than a Pd-bis-phosphate species generated through ligand exchanges.

  15. 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.

  16. Substitution scanning identifies a novel, catalytically active ibrutinib-resistant BTK cysteine 481 to threonine (C481T) variant.

    PubMed

    Hamasy, A; Wang, Q; Blomberg, K E M; Mohammad, D K; Yu, L; Vihinen, M; Berglöf, A; Smith, C I E

    2017-01-01

    Irreversible Bruton tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib have demonstrated remarkable clinical responses in multiple B-cell malignancies. Acquired resistance has been identified in a sub-population of patients in which mutations affecting BTK predominantly substitute cysteine 481 in the kinase domain for catalytically active serine, thereby ablating covalent binding of inhibitors. Activating substitutions in the BTK substrate phospholipase Cγ2 (PLCγ2) instead confers resistance independent of BTK. Herein, we generated all six possible amino acid substitutions due to single nucleotide alterations for the cysteine 481 codon, in addition to threonine, requiring two nucleotide substitutions, and performed functional analysis. Replacement by arginine, phenylalanine, tryptophan or tyrosine completely inactivated the catalytic activity, whereas substitution with glycine caused severe impairment. BTK with threonine replacement was catalytically active, similar to substitution with serine. We identify three potential ibrutinib resistance scenarios for cysteine 481 replacement: (1) Serine, being catalytically active and therefore predominating among patients. (2) Threonine, also being catalytically active, but predicted to be scarce, because two nucleotide changes are needed. (3) As BTK variants replaced with other residues are catalytically inactive, they presumably need compensatory mutations, therefore being very scarce. Glycine and tryptophan variants were not yet reported but likely also provide resistance.

  17. Substitution scanning identifies a novel, catalytically active ibrutinib-resistant BTK cysteine 481 to threonine (C481T) variant

    PubMed Central

    Hamasy, A; Wang, Q; Blomberg, K E M; Mohammad, D K; Yu, L; Vihinen, M; Berglöf, A; Smith, C I E

    2017-01-01

    Irreversible Bruton tyrosine kinase (BTK) inhibitors, ibrutinib and acalabrutinib have demonstrated remarkable clinical responses in multiple B-cell malignancies. Acquired resistance has been identified in a sub-population of patients in which mutations affecting BTK predominantly substitute cysteine 481 in the kinase domain for catalytically active serine, thereby ablating covalent binding of inhibitors. Activating substitutions in the BTK substrate phospholipase Cγ2 (PLCγ2) instead confers resistance independent of BTK. Herein, we generated all six possible amino acid substitutions due to single nucleotide alterations for the cysteine 481 codon, in addition to threonine, requiring two nucleotide substitutions, and performed functional analysis. Replacement by arginine, phenylalanine, tryptophan or tyrosine completely inactivated the catalytic activity, whereas substitution with glycine caused severe impairment. BTK with threonine replacement was catalytically active, similar to substitution with serine. We identify three potential ibrutinib resistance scenarios for cysteine 481 replacement: (1) Serine, being catalytically active and therefore predominating among patients. (2) Threonine, also being catalytically active, but predicted to be scarce, because two nucleotide changes are needed. (3) As BTK variants replaced with other residues are catalytically inactive, they presumably need compensatory mutations, therefore being very scarce. Glycine and tryptophan variants were not yet reported but likely also provide resistance. PMID:27282255

  18. Cu(II) Catalytic Reduction of Cr(VI) by Tartaric Acid Under the Irradiation of Simulated Solar Light

    PubMed Central

    Li, Ying; Qin, Chao; Zhang, Jing; Lan, Yeqing; Zhou, Lixiang

    2014-01-01

    Abstract Cu(II) catalytic reduction of Cr(VI) by tartaric acid under the irradiation of simulated solar light was investigated through batch experiments at pHs from 3 to 6 and at temperatures from 15°C to 35°C. Results demonstrated that introduction of Cu(II) could markedly improve reduction of Cr(VI) in comparison with tartaric acid alone. Optimal removal of Cr(VI) was achieved at pH 4. Reduction of Cr(VI) increased with increasing temperatures and initial concentrations of Cu(II) and tartaric acid. The catalytic role of Cu(II) in the reduction of Cr(VI) was ascribed to the formation of Cu(II)-tartaric acid complex, which generated active reductive intermediates, including Cu(I) and tartaric acid radicals through a pathway of metal–ligand–electron transfer with light. Cu(II) photocatalytic reduction of Cr(VI) by tartaric acid followed pseudo zero-order kinetics with regard to Cr(VI), and the activation energy was calculated to be 21.48 kJ/mol. To date, such a role of Cu(II) has not been reported. The results from the present study are helpful in fully understanding the photochemical reductive behavior of Cr(VI) in the presence of both tartaric acid and Cu(II) in soil and aquatic environments. PMID:25125941

  19. Cu(II) Catalytic Reduction of Cr(VI) by Tartaric Acid Under the Irradiation of Simulated Solar Light.

    PubMed

    Li, Ying; Qin, Chao; Zhang, Jing; Lan, Yeqing; Zhou, Lixiang

    2014-08-01

    Cu(II) catalytic reduction of Cr(VI) by tartaric acid under the irradiation of simulated solar light was investigated through batch experiments at pHs from 3 to 6 and at temperatures from 15°C to 35°C. Results demonstrated that introduction of Cu(II) could markedly improve reduction of Cr(VI) in comparison with tartaric acid alone. Optimal removal of Cr(VI) was achieved at pH 4. Reduction of Cr(VI) increased with increasing temperatures and initial concentrations of Cu(II) and tartaric acid. The catalytic role of Cu(II) in the reduction of Cr(VI) was ascribed to the formation of Cu(II)-tartaric acid complex, which generated active reductive intermediates, including Cu(I) and tartaric acid radicals through a pathway of metal-ligand-electron transfer with light. Cu(II) photocatalytic reduction of Cr(VI) by tartaric acid followed pseudo zero-order kinetics with regard to Cr(VI), and the activation energy was calculated to be 21.48 kJ/mol. To date, such a role of Cu(II) has not been reported. The results from the present study are helpful in fully understanding the photochemical reductive behavior of Cr(VI) in the presence of both tartaric acid and Cu(II) in soil and aquatic environments.

  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. Conversion of the refractory ammonia and acetic acid in catalytic wet air oxidation of animal byproducts.

    PubMed

    Fontanier, Virginie; Zalouk, Sofiane; Barbati, Stéphane

    2011-01-01

    Wet air oxidation (WAO) and catalytic wet air oxidation (CWAO) of slaughtered animal byproducts (ABPs) were investigated. Two step experiment was carried out consisting of a non-catalysed WAO run followed by a CWAO run at 170-275 degrees C, 20 MPa, and reaction time 180 min. The WAO (1st step) of sample (5 g/L total organic carbon (TOC)) yielded (82.0 +/- 4)% TOC removal and (78.4 +/- 13.2)% conversion of the initial organic-N into NH4(+)-N. Four metal catalysts (Pd, Pt, Rh, Ru) supported over alumina have been tested in catalytic WAO (2nd step) at elevated pH to enhance ammonia conversion and organic matter removal, particularly acetic acid. It was found that the catalysts Ru, Pt, and Rh had significant effects on the TOC removal (95.1%, 99.5% and 96.7%, respectively) and on the abatement of ammonia (93.4%, 96.7% and 96.3%, respectively) with high nitrogen selectivity. The catalyst Pd was found to have the less activity while Pt had the best performance. The X-Ray diffraction analysis showed that the support of catalyst was not stable under the experimental conditions since it reacted with phosphate present in solution. Nitrite and nitrate ions were monitored during the oxidation reaction and it was concluded that CWAO of ammonia in real waste treatment framework was in good agreement with the results obtained from the literature for ideal solutions of ammonia.

  2. 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.

  3. Catalytically active lead(ii)-imidazolium coordination assemblies with diversified lead(ii) coordination geometries.

    PubMed

    Naga Babu, Chatla; Suresh, Paladugu; Srinivas, Katam; Sathyanarayana, Arruri; Sampath, Natarajan; Prabusankar, Ganesan

    2016-05-10

    Five Pb(ii)-imidazolium carboxylate coordination assemblies with novel structural motifs were derived from the reaction between the corresponding flexible, semi flexible or rigid imidazolium carboxylic acid ligands and lead nitrate. The imidazolium linker present in these molecules likely plays a triple role such as the counter ion to balance the metal charge, the ligand being an integral part of the final product and the catalyst facilitating carbon-carbon bond formation reaction. These lead-imidazolium coordination assemblies exhibit, variable chemical and thermal stabilities, as well as catalytic activity. These newly prepared catalysts are highly active towards benzoin condensation reactions with good functional group tolerance.

  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. Size Effects in the Catalytic Activity of Unsupported Metallic Nanoparticles

    NASA Astrophysics Data System (ADS)

    Weber, Alfred P.; Seipenbusch, Martin; Kasper, Gerhard

    2003-08-01

    The influence of the size of nanoparticles on their catalytic activity was investigated for two systems on unsupported, i.e. gasborne nanoparticles. For the oxidation of hydrogen on Pt nanoparticle agglomerates, transport processes had to be taken into account to extract the real nanoparticle size effects. The results indicate an optimum particle size for the catalytic activity below 5nm which points clearly toward a real volume effect. In the case of the methanation reaction on gasborne Ni nanoparticles, no transport limitations were observed and the product concentration was directly proportional to the activity of the primary particles. We found an activity maximum for particles of about 19nm in diameter. This size is too large to be attributed to a real nanoparticle size effect induced by the electronic band structure. Therefore, we concluded that the particle size influences the adsorption behavior of the carbon monoxide molecules. In fact, it is known that intermediate adsorption enthalpies may favor dissociation processes, which is an essential step for the reaction, as manifested in the so called volcano-shaped curve. Then, in addition to the material dependence of the adsorption, we would also encounter a direct size dependence in the case of methanation on gasborne Ni nanoparticles.

  6. Catalytically active single-atom niobium in graphitic layers

    NASA Astrophysics Data System (ADS)

    Zhang, Xuefeng; Guo, Junjie; Guan, Pengfei; Liu, Chunjing; Huang, Hao; Xue, Fanghong; Dong, Xinglong; Pennycook, Stephen J.; Chisholm, Matthew F.

    2013-05-01

    Carbides of groups IV through VI (Ti, V and Cr groups) have long been proposed as substitutes for noble metal-based electrocatalysts in polymer electrolyte fuel cells. However, their catalytic activity has been extremely limited because of the low density and stability of catalytically active sites. Here we report the excellent performance of a niobium-carbon structure for catalysing the cathodic oxygen reduction reaction. A large number of single niobium atoms and ultra small clusters trapped in graphitic layers are directly identified using state-of-the-art aberration-corrected scanning transmission electron microscopy. This structure not only enhances the overall conductivity for accelerating the exchange of ions and electrons, but it suppresses the chemical/thermal coarsening of the active particles. Experimental results coupled with theory calculations reveal that the single niobium atoms incorporated within the graphitic layers produce a redistribution of d-band electrons and become surprisingly active for O2 adsorption and dissociation, and also exhibit high stability.

  7. 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.

  8. Catalytic activation of OKO zeolite with intersecting pores of 10- and 12-membered rings using atomic layer deposition of aluminium.

    PubMed

    Verheyen, E; Pulinthanathu Sree, S; Thomas, K; Dendooven, J; De Prins, M; Vanbutsele, G; Breynaert, E; Gilson, J-P; Kirschhock, C E A; Detavernier, C; Martens, J A

    2014-05-07

    Tetrahedral framework aluminium was introduced in all-silica zeolite -COK-14 using Atomic Layer Deposition (ALD) involving alternating exposure to trimethylaluminium and water vapour. The modification causes permanent conversion of the originally interrupted framework of -COK-14 to a fully connected OKO type framework, and generates catalytic activity in the acid catalysed hydrocarbon conversion reaction.

  9. [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.

  10. 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.

  11. Enhanced catalytic activity of solid and hollow platinum-cobalt nanoparticles towards reduction of 4-nitrophenol

    NASA Astrophysics Data System (ADS)

    Krajczewski, Jan; Kołątaj, Karol; Kudelski, Andrzej

    2016-12-01

    Previous investigations of hollow platinum nanoparticles have shown that such nanostructures are more active catalysts than their solid counterparts towards the following electrochemical reactions: reduction of oxygen, evolution of hydrogen, and oxidation of borohydride, methanol and formic acid. In this work we show that synthesised using standard galvanic replacement reaction (with Co templates) hollow platinum nanoparticles exhibit enhanced catalytic activity also towards reduction of 4-nitrophenol by sodium borohydride in water. Unlike in the case of procedures involving hollow platinum catalysts employed so far to carry out this reaction it is not necessary to couple analysed platinum nanoparticles to the surface of an electrode. Simplification of the analyzed reaction may eliminate same experimental errors. We found that the enhanced catalytic activity of hollow Pt nanoparticles is not only connected with generally observed larger surface area of hollow nanostructures, but is also due to the contamination of formed hollow nanostructures with cobalt, from which sacrificial templates used in the synthesis of hollow Pt nanostrustures have been formed. Because using sacrificial templates is a typical method of synthesis of hollow metal nanostructures, formed hollow nanoparticles are probably often contaminated, which may significantly influence their catalytic activity.

  12. [Mechanism of catalytic ozonation for the degradation of paracetamol by activated carbon].

    PubMed

    Wang, Jia-Yu; Dai, Qi-Zhou; Yu, Jie; Yan, Yi-Zhou; Chen, Jian-Meng

    2013-04-01

    The degradation of paracetamol (APAP) in aqueous solution was studied with ozonation integrated with activated carbon (AC). The synergistic effect of ozonation/AC process was explored by comparing the degradation efficiency of APAP in three processes (ozonation alone, activated carbon alone and ozonation integrated with activated carbon). The operational parameters that affected the reaction rate were carefully optimized. Based on the intermediates detected, the possible pathway for catalytic degradation was discussed and the reaction mechanism was also investigated. The results showed that the TOC removal reached 55.11% at 60 min in the AC/O3 system, and was significantly better than the sum of ozonation alone (20.22%) and activated carbon alone (27.39%), showing the great synergistic effect. And the BOD5/COD ratio increased from 0.086 (before reaction) to 0.543 (after reaction), indicating that the biodegradability was also greatly improved. The effects of the initial concentration of APAP, pH value, ozone dosage and AC dosage on the variation of reaction rate were carefully discussed. The catalytic reaction mechanism was different at different pH values: the organic pollutions were removed by adsorption and direct ozone oxidation at acidic pH, and mainly by catalytic ozonation at alkaline pH.

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

    PubMed

    Lim, Hee Nam; Dong, Guangbin

    2015-12-07

    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.

  14. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining.

    PubMed

    Buurmans, Inge L C; Ruiz-Martínez, Javier; Knowles, William V; van der Beek, David; Bergwerff, Jaap A; Vogt, Eelco T C; Weckhuysen, Bert M

    2011-09-18

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  15. Catalytic activity in individual cracking catalyst particles imaged throughout different life stages by selective staining

    NASA Astrophysics Data System (ADS)

    Buurmans, Inge L. C.; Ruiz-Martínez, Javier; Knowles, William V.; van der Beek, David; Bergwerff, Jaap A.; Vogt, Eelco T. C.; Weckhuysen, Bert M.

    2011-11-01

    Fluid catalytic cracking (FCC) is the major conversion process used in oil refineries to produce valuable hydrocarbons from crude oil fractions. Because the demand for oil-based products is ever increasing, research has been ongoing to improve the performance of FCC catalyst particles, which are complex mixtures of zeolite and binder materials. Unfortunately, there is limited insight into the distribution and activity of individual zeolitic domains at different life stages. Here we introduce a staining method to visualize the structure of zeolite particulates and other FCC components. Brønsted acidity maps have been constructed at the single particle level from fluorescence microscopy images. By applying a statistical methodology to a series of catalysts deactivated via industrial protocols, a correlation is established between Brønsted acidity and cracking activity. The generally applicable method has clear potential for catalyst diagnostics, as it determines intra- and interparticle Brønsted acidity distributions for industrial FCC materials.

  16. Acid activated montmorillonite as catalysts in methyl esterification reactions of lauric acid.

    PubMed

    Zatta, Leandro; Ramos, Luiz Pereira; Wypych, Fernando

    2012-01-01

    The catalytic activity of acid activated montmorillonite in the esterification of free fatty acids (FFA) is reported. Standard Montmorillonite (MMT) type STx-1 provided by the Clay Mineral Society repository was activated using phosphoric, nitric and sulphuric acids under different conditions and the resulting materials were characterized and evaluated as catalysts in the methyl esterification of lauric acid. Blank reactions carried out in the absence of any added catalyst presented conversions of 32.64, 69.79 and 79.23%, for alcohol:lauric acid molar ratios of 60:1, 12:1 and 6:1, respectively. In the presence of the untreated clay and using molar ratios of 12:1 and 6:1 with 12% of catalyst, conversions of 70.92 and 82.30% were obtained, respectively. For the acid activated clays, conversions up to 93.08% of lauric acid to methyl laurate were obtained, much higher than those observed for the thermal conversion or using untreated montmorillonite. Relative good correlations were observed between the catalytic activity and the development of acid sites and textural properties of the resulting materials. Therefore, a simple acid activation was able to improve the catalytic activity and produce clay catalysts that are environmental friendly, cost effective, noncorrosive and reusable.

  17. 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.

  18. 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

  19. 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.

  20. Activated carbon and tungsten oxide supported on activated carbon catalysts for toluene catalytic combustion.

    PubMed

    Alvarez-Merino, M A; Ribeiro, M F; Silva, J M; Carrasco-Marín, F; Maldonado-Hódar, F J

    2004-09-01

    We have used activated carbon (AC) prepared from almond shells as a support for tungsten oxide to develop a series of WOx/AC catalysts for the catalytic combustion of toluene. We conducted the reaction between 300 and 350 degrees C, using a flow of 500 ppm of toluene in air and space velocity (GHSV) in the range 4000-7000 h(-1). Results show that AC used as a support is an appropriate material for removing toluene from dilute streams. By decreasing the GHSV and increasing the reaction temperature AC becomes a specific catalyst for the total toluene oxidation (SCO2 = 100%), but in less favorable conditions CO appears as reaction product and toluene-derivative compounds are retained inside the pores. WOx/AC catalysts are more selective to CO2 than AC due to the strong acidity of this oxide; this behavior improves with increased metal loading and reaction temperature and contact time. The catalytic performance depends on the nonstoichiometric tungsten oxide obtained during the pretreatment. In comparison with other supports the WOx/AC catalysts present, at low reaction temperatures, higher activity and selectivity than WO, supported on SiO2, TiO2, Al2O3, or Y zeolite. This is due to the hydrophobic character of the AC surface which prevents the adsorption of water produced from toluene combustion thus avoiding the deactivation of the active centers. However, the use of WOx/AC system is always restricted by its gasification temperature (around 400 degrees C), which limits the ability to increase the conversion values by increasing reaction temperatures.

  1. 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

  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.

  3. Catalytic activation of carbon-carbon bonds in cyclopentanones.

    PubMed

    Xia, Ying; Lu, Gang; Liu, Peng; Dong, Guangbin

    2016-11-24

    In the chemical industry, molecules of interest are based primarily on carbon skeletons. When synthesizing such molecules, the activation of carbon-carbon single bonds (C-C bonds) in simple substrates is strategically important: it offers a way of disconnecting such inert bonds, forming more active linkages (for example, between carbon and a transition metal) and eventually producing more versatile scaffolds. The challenge in achieving such activation is the kinetic inertness of C-C bonds and the relative weakness of newly formed carbon-metal bonds. The most common tactic starts with a three- or four-membered carbon-ring system, in which strain release provides a crucial thermodynamic driving force. However, broadly useful methods that are based on catalytic activation of unstrained C-C bonds have proven elusive, because the cleavage process is much less energetically favourable. Here we report a general approach to the catalytic activation of C-C bonds in simple cyclopentanones and some cyclohexanones. The key to our success is the combination of a rhodium pre-catalyst, an N-heterocyclic carbene ligand and an amino-pyridine co-catalyst. When an aryl group is present in the C3 position of cyclopentanone, the less strained C-C bond can be activated; this is followed by activation of a carbon-hydrogen bond in the aryl group, leading to efficient synthesis of functionalized α-tetralones-a common structural motif and versatile building block in organic synthesis. Furthermore, this method can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids. Density functional theory calculations reveal a mechanism involving an intriguing rhodium-bridged bicyclic intermediate.

  4. 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

  5. Catalytic activity of rhodium complex immobilized on AN-31 ion exchanger

    SciTech Connect

    Parshikova, G.N.; Korneva, L.I.; Kononov, Yu.S.

    1995-08-10

    Immobilized platinum-metal complexes are of interest as heterogeneous catalysts. Ion-exchange resins may be used as supports for catalytically active complexes. However, immobilized metal complexes are often unstable, are washed out from supports, and are lost with reaction products. Secure immobilization of metal complexes on supports is possible, for example, via coordination of the central metal by electron-donor groups of the support. This is the case when platinum metals are sorbed from solutions by nitrogen-containing ion exchangers. Complexes thus immobilized have high catalytic activity. Previously the authors demonstrated that rhodium(III) is sorbed from solutions containing rhodium aqua-chloro complexes as stable complexes with AN-31. These complexes were not desorbed with 10 M hydrochloric acid. Stable amino complexes of transition metals sorbed on ion exchangers are known to be active in decomposition of hydrogen peroxide. In this work, the authors have studied catalytic properties of rhodium complex with the ion exchanger under atmospheric pressure at 25-80{degrees}C.

  6. Balancing the stability and the catalytic specificities of OP hydrolases with enhanced V-agent activities.

    PubMed

    Reeves, T E; Wales, M E; Grimsley, J K; Li, P; Cerasoli, D M; Wild, J R

    2008-06-01

    Rational site-directed mutagenesis and biophysical analyses have been used to explore the thermodynamic stability and catalytic capabilities of organophosphorus hydrolase (OPH) and its genetically modified variants. There are clear trade-offs in the stability of modifications that enhance catalytic activities. For example, the H254R/H257L variant has higher turnover numbers for the chemical warfare agents VX (144 versus 14 s(-1) for the native enzyme (wild type) and VR (Russian VX, 465 versus 12 s(-1) for wild type). These increases are accompanied by a loss in stability in which the total Gibb's free energy for unfolding is 19.6 kcal/mol, which is 5.7 kcal/mol less than that of the wild-type enzyme. X-ray crystallographic studies support biophysical data that suggest amino acid residues near the active site contribute to the chemical and thermal stability through hydrophobic and cation-pi interactions. The cation-pi interactions appear to contribute an additional 7 kcal/mol to the overall global stability of the enzyme. Using rational design, it has been possible to make amino acid changes in this region that restored the stability, yet maintained effective V-agent activities, with turnover numbers of 68 and 36 s(-1) for VX and VR, respectively. This study describes the first rationally designed, stability/activity balance for an OPH enzyme with a legitimate V-agent activity, and its crystal structure.

  7. 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.

  8. Deaminative and decarboxylative catalytic alkylation of amino acids with ketones.

    PubMed

    Kalutharage, Nishantha; Yi, Chae S

    2013-12-16

    It cuts two ways: The cationic [Ru-H] complex catalyzes selective coupling of α- and β-amino acids with ketones to form α-alkylated ketone products. The reaction involves CC and CN bond cleavage which result in regio- and stereoselective alkylation using amino acids. A broad substrate scope and high functional-group tolerance is demonstrated.

  9. Molecular dynamics simulation and conformational analysis of some catalytically active peptides.

    PubMed

    Honarparvar, Bahareh; Skelton, Adam A

    2015-04-01

    The design of stable and inexpensive artificial enzymes with potent catalytic activity is a growing field in peptide science. The first step in this design process is to understand the key factors that can affect the conformational preference of an enzyme and correlate them with its catalytic activity. In this work, molecular dynamics simulations in explicit water of two catalytically active peptides (peptide 1: Fmoc-Phe1-Phe2-His-CONH2; peptide 2: Fmoc-Phe1-Phe2-Arg-CONH2) were performed at temperatures of 300, 400, and 500 K. Conformational analysis of these peptides using Ramachandran plots identified the secondary structures of the amino acid residues involved (Phe1, Phe2, His, Arg) and confirmed their conformational flexibility in solution. Furthermore, Ramachandran maps revealed the intrinsic preference of the constituent residues of these compounds for a helical conformation. Long-range interaction distances and radius of gyration (R g) values obtained during 20 ns MD simulations confirmed their tendency to form folded conformations. Results showed a decrease in side-chain (Phe1, Phe2, His ring, and Arg) contacts as the temperature was raised from 300 to 400 K and then to 500 K. Finally, the radial distribution functions (RDF) of the water molecules around the nitrogen atoms in the catalytically active His and Arg residues of peptide 1 and peptide 2 revealed that the strongest water-peptide interaction occurred with the arginine nitrogen atoms in peptide 2. Our results highlight differences in the secondary structures of the two peptides that can be explained by the different arrangement of water molecules around the nitrogen atoms of Arg in peptide 2 as compared to the arrangement of water molecules around the nitrogen atoms of His in peptide 1. The results of this work thus provide detailed insight into peptide conformations which can be exploited in the future design of peptide analogs.

  10. Sequence of the bphD gene encoding 2-hydroxy-6-oxo-(phenyl/chlorophenyl)hexa-2,4-dienoic acid (HOP/cPDA) hydrolase involved in the biphenyl/polychlorinated biphenyl degradation pathway in Comamonas testosteroni: evidence suggesting involvement of Ser112 in catalytic activity.

    PubMed

    Ahmad, D; Fraser, J; Sylvestre, M; Larose, A; Khan, A; Bergeron, J; Juteau, J M; Sondossi, M

    1995-04-14

    The nucleotide sequence of bphD, encoding 2-hydroxy-6-oxo-(phenyl/chlorophenyl)hexa-2,4-dienoic acid hydrolase involved in the biphenyl/polychlorinated biphenyl degradation pathway of Comamonas testosteroni strain B-356, was determined. Comparison of the deduced amino-acid sequence with published sequences led to the identification of a 'lipase box', containing a consensus pentapeptide sequence GlyXaaSerXaaGly. This suggested that the mechanism of action of this enzyme may involve an Asp-Ser-His catalytic triad similar to that of classical lipases and serine hydrolases. Further biochemical and genetic evidence for the active-site involvement of Ser112 was obtained by showing that a semipurified enzyme was inhibited by PMSF, a classic inhibitor of serine hydrolases, and by site-directed Ser112-->Ala mutagenesis.

  11. 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.

  12. Face the Edges: Catalytic Active Sites of Nanomaterials

    PubMed Central

    Ni, Bing

    2015-01-01

    Edges are special sites in nanomaterials. The atoms residing on the edges have different environments compared to those in other parts of a nanomaterial and, therefore, they may have different properties. Here, recent progress in nanomaterial fields is summarized from the viewpoint of the edges. Typically, edge sites in MoS2 or metals, other than surface atoms, can perform as active centers for catalytic reactions, so the method to enhance performance lies in the optimization of the edge structures. The edges of multicomponent interfaces present even more possibilities to enhance the activities of nanomaterials. Nanoframes and ultrathin nanowires have similarities to conventional edges of nanoparticles, the application of which as catalysts can help to reduce the use of costly materials. Looking beyond this, the edge structures of graphene are also essential for their properties. In short, the edge structure can influence many properties of materials. PMID:27980960

  13. 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.

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

    NASA Astrophysics Data System (ADS)

    Ooi, Mahayatun Dayana Johan; Aziz, Azlan Abdul

    2015-04-01

    Flower-like Platinum micro-structures were synthesized from different concentration of the PVP using solvothermal method. At 5.0×10-3 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 5.0×10-3 mmol PVP exhibit the highest catalytic activity and stability towards electro-oxidation of formic acid.

  15. Using heat pipe to make isotherm condition in catalytic converters of sulfuric acid plants

    NASA Astrophysics Data System (ADS)

    Yousefi, M.; Pahlavanzadeh, H.; Sadrameli, S. M.

    2017-03-01

    In this study, for the first time, it is tried to construct a pilot reactor, for surveying the possibility of creating isothermal condition in the catalytic convertors where SO2 is converted to SO3 in the sulfuric acid plants by heat pipe. The thermodynamic and thermo-kinetic conditions were considered the same as the sulfuric acid plants converters. Also, influence of SO2 gas flow rate on isothermal condition, has been studied. A thermo-siphon type heat pipe contains the sulfur + 5% iodine as working fluid, was used for disposing the heat of reaction from catalytic bed. Our results show that due to very high energy-efficiency, isothermal and passive heat transfer mechanism of heat pipe, it is possible to reach more than 95% conversion in one isothermal catalytic bed. As the results, heat pipe can be used as a certain piece of equipment to create isothermal condition in catalytic convertors of sulphuric acid plants. With this work a major evaluation in design of sulphuric acid plants can be taken place.

  16. 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.)

  17. Importance of the lid and cap domains for the catalytic activity of gastric lipases.

    PubMed

    Miled, N; Bussetta, C; De caro, A; Rivière, M; Berti, L; Canaan, S

    2003-09-01

    Human gastric lipase (HGL) is an enzyme secreted by the stomach, which is stable and active despite the highly acidic environment. It has been clearly established that this enzyme is responsible for 30% of the fat digestion processes occurring in human. This globular protein belongs to the alpha/beta hydrolase fold family and its catalytic serine is deeply buried under a domain called the extrusion domain, which is composed of a 'cap' domain and a segment consisting of 58 residues, which can be defined as a lid. The exact roles played by the cap and the lid domains during the catalytic step have not yet been elucidated. We have recently solved the crystal structure of the open form of the dog gastric lipase in complex with a covalent inhibitor. The detergent molecule and the inhibitor were mimicking a triglyceride substrate that would interact with residues belonging to both the cap and the lid domains. In this study, we have investigated the role of the cap and the lid domains, using site-directed mutagenesis procedures. We have produced truncated mutants lacking the lid and the cap. After expressing these mutants and purifying them, their activity was found to have decreased drastically in comparison with the wild type HGL. The lid and the cap domains play an important role in the catalytic reaction mechanism. Based on these results and the structural data (open form of DGL), we have pointed out the cap and the lid residues involved in the binding with the lipidic substrate.

  18. 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.

  19. A simple and sensitive flow injection method based on the catalytic activity of CdS quantum dots in an acidic permanganate chemiluminescence system for determination of formaldehyde in water and wastewater.

    PubMed

    Khataee, Alireza; Lotfi, Roya; Hasanzadeh, Aliyeh; Iranifam, Mortaza

    2016-04-01

    A simple and sensitive flow injection chemiluminescence (CL) method in which CdS quantum dots (QDs) enhanced the CL intensity of a KMnO4-formaldehyde (HCHO) reaction was offered for the determination of HCHO. This CL system was based on the catalytic activity of CdS QDs and their participation in the CL resonance energy transfer (CRET) phenomenon. A possible mechanism for the supplied CL system was proposed using the kinetic curves of the CL systems and the spectra of CL, photoluminescence (PL) and ultraviolet-visible (UV-Vis). The emanated CL intensity of the KMnO4-CdS QDs system was amplified in the presence of a trace level of HCHO. Based on this enhancement effect, a simple and sensitive flow injection CL method was suggested for the determination of HCHO concentration in environmental water and wastewater samples. Under selected optimized experimental conditions, the increased CL intensity was proportional to the HCHO concentration in the range of 0.03-4.5 μg L(-1) and 4.5-10.0 μg L(-1). The detection limits (3σ) were 0.0003 μg L(-1) and 1.2 μg L(-1). The relative standard deviations (RSD%) for eleven replicate determinations of 4.0 μg L(-1) HCHO were 2.2%. Furthermore, the feasibility of the developed method was investigated via the determination of HCHO concentration in environmental water and wastewater samples.

  20. 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.

  1. [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.

  2. Support nanostructure boosts oxygen transfer to catalytically active platinum nanoparticles.

    PubMed

    Vayssilov, Georgi N; Lykhach, Yaroslava; Migani, Annapaola; Staudt, Thorsten; Petrova, Galina P; Tsud, Nataliya; Skála, Tomáš; Bruix, Albert; Illas, Francesc; Prince, Kevin C; Matolín, Vladimír; Neyman, Konstantin M; Libuda, Jörg

    2011-04-01

    Interactions of metal particles with oxide supports can radically enhance the performance of supported catalysts. At the microscopic level, the details of such metal-oxide interactions usually remain obscure. This study identifies two types of oxidative metal-oxide interaction on well-defined models of technologically important Pt-ceria catalysts: (1) electron transfer from the Pt nanoparticle to the support, and (2) oxygen transfer from ceria to Pt. The electron transfer is favourable on ceria supports, irrespective of their morphology. Remarkably, the oxygen transfer is shown to require the presence of nanostructured ceria in close contact with Pt and, thus, is inherently a nanoscale effect. Our findings enable us to detail the formation mechanism of the catalytically indispensable Pt-O species on ceria and to elucidate the extraordinary structure-activity dependence of ceria-based catalysts in general.

  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.

  4. Orthogonal gene knock out and activation with a catalytically active Cas9 nuclease

    PubMed Central

    Dahlman, James E.; Abudayyeh, Omar O.; Joung, Julia; Gootenberg, Jonathan S.; Zhang, Feng; Konermann, Silvana

    2015-01-01

    We have developed a CRISPR-based method that uses catalytically active Cas9 and distinct sgRNA constructs to knock out and activate different genes in the same cell. These sgRNAs, with 14 15 bp target sequences and MS2 binding loops, can activate gene expression using an active Cas9 nuclease, without inducing DSBs. We use these ‘dead RNAs’ to perform orthogonal gene knockout and transcriptional activation in human cells. PMID:26436575

  5. 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.

  6. 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

  7. Reduced graphene oxide: firm support for catalytically active palladium nanoparticles and game changer in selective hydrogenation reactions.

    PubMed

    Cano, Manuela; Benito, Ana M; Urriolabeitia, Esteban P; Arenal, Raul; Maser, Wolfgang K

    2013-11-07

    Simultaneous decomposition and reduction of a Pd(2+) complex in the presence of graphene oxide (GO) lead to the formation of Pd(0)-nanoparticles (Pd-NPs) with average sizes of 4 nm firmly anchored on reduced graphene oxide (RGO) sheets. The Pd-NP/RGO hybrids exhibited remarkable catalytic activity and selectivity in mild hydrogenation reactions where the acidic properties of RGO play an active role and may act as an important game-changer.

  8. 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.

  9. Cholinesterase-like domains in enzymes and structural proteins: functional and evolutionary relationships and identification of a catalytically essential aspartic acid.

    PubMed Central

    Krejci, E; Duval, N; Chatonnet, A; Vincens, P; Massoulié, J

    1991-01-01

    Primary sequences of cholinesterases and related proteins have been systematically compared. The cholinesterase-like domain of these proteins, about 500 amino acids, may fulfill a catalytic and a structural function. We identified an aspartic acid residue that is conserved among esterases and lipases (Asp-397 in Torpedo acetylcholinesterase) but that had not been considered to be involved in the catalytic mechanism. Site-directed mutagenesis demonstrated that this residue is necessary for activity. Analysis of evolutionary relationships shows that the noncatalytic members of the family do not constitute a separate subgroup, suggesting that loss of catalytic activity occurred independently on several occasions, probably from bifunctional molecules. Cholinesterases may thus be involved in cell-cell interactions in addition to the hydrolysis of acetylcholine. This would explain their specific expression in well-defined territories during embryogenesis before the formation of cholinergic synapses and their presence in noncholinergic tissues. Images PMID:1862088

  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. Screening for catalytically active Type II restriction endonucleases using segregation-induced methylation deficiency

    PubMed Central

    Ukanis, Mindaugas; Sapranauskas, Rimantas; Lubys, Arvydas

    2012-01-01

    Type II restriction endonucleases (REases) are one of the basic tools of recombinant DNA technology. They also serve as models for elucidation of mechanisms for both site-specific DNA recognition and cleavage by proteins. However, isolation of catalytically active mutants from their libraries is challenging due to the toxicity of REases in the absence of protecting methylation, and techniques explored so far had limited success. Here, we present an improved SOS induction-based approach for in vivo screening of active REases, which we used to isolate a set of active variants of the catalytic mutant, Cfr10IE204Q. Detailed characterization of plasmids from 64 colonies screened from the library of ∼200 000 transformants revealed 29 variants of cfr10IR gene at the level of nucleotide sequence and 15 variants at the level of amino acid sequence, all of which were able to induce SOS response. Specific activity measurements of affinity-purified mutants revealed >200-fold variance among them, ranging from 100% (wild-type isolates) to 0.5% (S188C mutant), suggesting that the technique is equally suited for screening of mutants possessing high or low activity and confirming that it may be applied for identification of residues playing a role in catalysis. PMID:22753027

  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. 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

  14. Prediction of hammerhead ribozyme intracellular activity with the catalytic core fingerprint.

    PubMed

    Gabryelska, Marta Magdalena; Wyszko, Eliza; Szymański, Maciej; Popenda, Mariusz; Barciszewski, Jan

    2013-05-01

    Hammerhead ribozyme is a versatile tool for down-regulation of gene expression in vivo. Owing to its small size and high activity, it is used as a model for RNA structure-function relationship studies. In the present paper we describe a new extended hammerhead ribozyme HH-2 with a tertiary stabilizing motif constructed on the basis of the tetraloop receptor sequence. This ribozyme is very active in living cells, but shows low activity in vitro. To understand it, we analysed tertiary structure models of substrate-ribozyme complexes. We calculated six unique catalytic core geometry parameters as distances and angles between particular atoms that we call the ribozyme fingerprint. A flanking sequence and tertiary motif change the geometry of the general base, general acid, nucleophile and leaving group. We found almost complete correlation between these parameters and the decrease of target gene expression in the cells. The tertiary structure model calculations allow us to predict ribozyme intracellular activity. Our approach could be widely adapted to characterize catalytic properties of other RNAs.

  15. Simultaneous pore enlargement and introduction of highly dispersed Fe active sites in MSNs for enhanced catalytic activity

    SciTech Connect

    Gu Jinlou; Dong Xu; Elangovan, S.P.; Li Yongsheng; Zhao Wenru; Iijima, Toshio; Yamazaki, Yasuo; Shi Jianlin

    2012-02-15

    An effective post-hydrothermal treatment strategy has been developed to dope highly dispersed iron catalytical centers into the framework of mesoporous silica, to keep the particle size in nanometric scale, and in the meanwhile, to expand the pore size of the synthesized mesoporous silica nanoparticles (MSNs). Characterization techniques such as XRD, BET, SEM and TEM support that the synthesized samples are long period ordered with particles size about 100 nm and a relatively large pore size of ca. 3.5 nm. UV-vis, XPS and EPR measurements demonstrate that the introduced iron active centers are highly dispersed in a coordinatively unsaturated status. NH{sub 3}-TPD verifies that the acid amount of iron-doped MSNs is quite high. The synthesized nanocatalysts show an excellent catalytic performance for benzylation of benzene by benzyl chloride, and they present relatively higher yield and selectivity to diphenylmethane with a lower iron content and much shorter reaction time. - Graphical abstract: Uniform MSNs with iron active centers and large pore size have been prepared by a newly developed strategy, which demonstrates enhanced catalytic performance for benzylation of benzene by benzyl chloride. Highlights: Black-Right-Pointing-Pointer Iron species were introduced into the framework of mesoporous silica nanoparticles with uniform dispersion. Black-Right-Pointing-Pointer The pore sizes of the synthesized nanocatalysts were expanded. Black-Right-Pointing-Pointer The acidic site quantities were quite high and the acidic centers were accessible. Black-Right-Pointing-Pointer The nanocatalysts presented higher yield and selectivity to diphenylmethane with significantly lower Fe content.

  16. 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.

  17. 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

  18. 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

  19. [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.

  20. 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.

  1. 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.

  2. 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.

  3. Green Synthesis and Catalytic Activity of Gold Nanoparticles Synthesized by Artemisia capillaris Water Extract.

    PubMed

    Lim, Soo Hyeon; Ahn, Eun-Young; Park, Youmie

    2016-12-01

    Gold nanoparticles were synthesized using a water extract of Artemisia capillaris (AC-AuNPs) under different extract concentrations, and their catalytic activity was evaluated in a 4-nitrophenol reduction reaction in the presence of sodium borohydride. The AC-AuNPs showed violet or wine colors with characteristic surface plasmon resonance bands at 534~543 nm that were dependent on the extract concentration. Spherical nanoparticles with an average size of 16.88 ± 5.47~29.93 ± 9.80 nm were observed by transmission electron microscopy. A blue shift in the maximum surface plasmon resonance was observed with increasing extract concentration. The face-centered cubic structure of AC-AuNPs was confirmed by high-resolution X-ray diffraction analysis. Based on phytochemical screening and Fourier transform infrared spectra, flavonoids, phenolic compounds, and amino acids present in the extract contributed to the reduction of Au ions to AC-AuNPs. The average size of the AC-AuNPs decreased as the extract concentration during the synthesis was increased. Higher 4-nitrophenol reduction reaction rate constants were observed for smaller sizes. The extract in the AC-AuNPs was removed by centrifugation to investigate the effect of the extract in the reduction reaction. Interestingly, the removal of extracts greatly enhanced their catalytic activity by up to 50.4 %. The proposed experimental method, which uses simple centrifugation, can be applied to other metallic nanoparticles that are green synthesized with plant extracts to enhance their catalytic activity.

  4. Green Synthesis and Catalytic Activity of Gold Nanoparticles Synthesized by Artemisia capillaris Water Extract

    NASA Astrophysics Data System (ADS)

    Lim, Soo Hyeon; Ahn, Eun-Young; Park, Youmie

    2016-10-01

    Gold nanoparticles were synthesized using a water extract of Artemisia capillaris (AC-AuNPs) under different extract concentrations, and their catalytic activity was evaluated in a 4-nitrophenol reduction reaction in the presence of sodium borohydride. The AC-AuNPs showed violet or wine colors with characteristic surface plasmon resonance bands at 534 543 nm that were dependent on the extract concentration. Spherical nanoparticles with an average size of 16.88 ± 5.47 29.93 ± 9.80 nm were observed by transmission electron microscopy. A blue shift in the maximum surface plasmon resonance was observed with increasing extract concentration. The face-centered cubic structure of AC-AuNPs was confirmed by high-resolution X-ray diffraction analysis. Based on phytochemical screening and Fourier transform infrared spectra, flavonoids, phenolic compounds, and amino acids present in the extract contributed to the reduction of Au ions to AC-AuNPs. The average size of the AC-AuNPs decreased as the extract concentration during the synthesis was increased. Higher 4-nitrophenol reduction reaction rate constants were observed for smaller sizes. The extract in the AC-AuNPs was removed by centrifugation to investigate the effect of the extract in the reduction reaction. Interestingly, the removal of extracts greatly enhanced their catalytic activity by up to 50.4 %. The proposed experimental method, which uses simple centrifugation, can be applied to other metallic nanoparticles that are green synthesized with plant extracts to enhance their catalytic activity.

  5. Simple and rapid hydrogenation of p-nitrophenol with aqueous formic acid in catalytic flow reactors.

    PubMed

    Javaid, Rahat; Kawasaki, Shin-Ichiro; Suzuki, Akira; Suzuki, Toshishige M

    2013-01-01

    The inner surface of a metallic tube (i.d. 0.5 mm) was coated with a palladium (Pd)-based thin metallic layer by flow electroless plating. Simultaneous plating of Pd and silver (Ag) from their electroless-plating solution produced a mixed distributed bimetallic layer. Preferential acid leaching of Ag from the Pd-Ag layer produced a porous Pd surface. Hydrogenation of p-nitrophenol was examined in the presence of formic acid simply by passing the reaction solution through the catalytic tubular reactors. p-Aminophenol was the sole product of hydrogenation. No side reaction occurred. Reaction conversion with respect to p-nitrophenol was dependent on the catalyst layer type, the temperature, pH, amount of formic acid, and the residence time. A porous and oxidized Pd (PdO) surface gave the best reaction conversion among the catalytic reactors examined. p-Nitrophenol was converted quantitatively to p-aminophenol within 15 s of residence time in the porous PdO reactor at 40 °C. Evolution of carbon dioxide (CO2) was observed during the reaction, although hydrogen (H2) was not found in the gas phase. Dehydrogenation of formic acid did not occur to any practical degree in the absence of p-nitrophenol. Consequently, the nitro group was reduced via hydrogen transfer from formic acid to p-nitrophenol and not by hydrogen generated by dehydrogenation of formic acid.

  6. 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

    2015-12-02

    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

  7. Decolorization of orange II by catalytic oxidation using iron (III) phthalocyanine-tetrasulfonic acid.

    PubMed

    Rismayani, Sinta; Fukushima, Masami; Ichikawa, Hiroyasu; Tatsumi, Kenji

    2004-10-18

    Orange II, C.I. Acid Orange 7 (AO7), is oxidatively decolorized via catalytic oxidation by iron(III) phthalocyanine-tetrasulfonic acid (Fe(III)-PcTS) as a biomimetic catalyst and KHSO(5) as an oxygen donor. The nature of the decolorization of AO7 was investigated in the catalyst concentration range of 10-50 microM, in which the initial concentration of AO7 was 417 mg l(-1). A 99.6% decolorization was observed at [KHSO(5)] = 2.5 mM and [Fe(III)-PcTS] = 20 microM after a 3-h reaction period. However, the fact that only 4.9% of the TOC was removed indicated that the conversion to CO(2) was incomplete. The results of a total organic nitrogen analysis of the reaction mixture showed that the nitrogen in the azo chain was mainly converted to N(2) gas. In addition, 38.6% of the AO7 was converted to 1,2-dihydroxynaphthalene, and 21.4% to p-phenolsulfonic acid. These results indicate that the degradation via this catalytic system involves the conversion of AO7 to phenolic compounds, followed by N(2) production. In addition, a Microtox test showed that toxicity of the solution increased as a result of AO7 oxidation using this catalytic system.

  8. 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.

  9. [Role of hydrophobic interactions in manifestation of catalytic activity of lipolytic enzymes].

    PubMed

    Rakhimov, M M; Dzhanbaeva, N R

    1977-06-01

    Kinetics is studied of enzymatic hydrolysis of different substrates of soluble and immobilized cotton lipase. At least two stages of enzymatic lipolysis are found to take place, which precede the formation of Mikhaelis complex: 1) the enzyme adsorption on substrate phase surface and 2) lipase activation. The latter is accompanied by the formation of local chamber on phase contact area in which the hydrolysis occurs. It is suggested on the basis of data on the inhibition by a number of phenylcarbonic acids and fluoride ions, on the hydrolysis rate of soluble and insoluble substrates, catalysed by different immobilized lipases, that there are three regions in the active center of lipolytic enzymes: 1) a region responsible for the "recognition" of substrate phase surface; 2) a binding region, participating in hydrophobic interaction with a single substrate molecule, located in the insoluble phase; 3) catalytical region. A hypothetic scheme of lipid enzymatic hydrolysis at phase contact area is given.

  10. Non-cell autonomous and non-catalytic activities of ATX in the developing brain.

    PubMed

    Greenman, Raanan; Gorelik, Anna; Sapir, Tamar; Baumgart, Jan; Zamor, Vanessa; Segal-Salto, Michal; Levin-Zaidman, Smadar; Aidinis, Vassilis; Aoki, Junken; Nitsch, Robert; Vogt, Johannes; Reiner, Orly

    2015-01-01

    The intricate formation of the cerebral cortex requires a well-coordinated series of events, which are regulated at the level of cell-autonomous and non-cell autonomous mechanisms. Whereas cell-autonomous mechanisms that regulate cortical development are well-studied, the non-cell autonomous mechanisms remain poorly understood. A non-biased screen allowed us to identify Autotaxin (ATX) as a non-cell autonomous regulator of neural stem cells. ATX (also known as ENPP2) is best known to catalyze lysophosphatidic acid (LPA) production. Our results demonstrate that ATX affects the localization and adhesion of neuronal progenitors in a cell autonomous and non-cell autonomous manner, and strikingly, this activity is independent from its catalytic activity in producing LPA.

  11. Tailoring micro-mesoporosity in activated carbon fibers to enhance SO₂ catalytic oxidation.

    PubMed

    Diez, Noel; Alvarez, Patricia; Granda, Marcos; Blanco, Clara; Gryglewicz, Grażyna; Wróbel-Iwaniec, Iwona; Sliwak, Agata; Machnikowski, Jacek; Menendez, Rosa

    2014-08-15

    Enhanced SO2 adsorption of activated carbon fibers is obtained by tailoring a specific micro-mesoporous structure in the fibers. This architecture is obtained via metal catalytic activation of the fibers with a novel precursor, cobalt naphthenate, which contrary to other precursors, also enhances spinnability and carbon fiber yield. In the SO2 oxidation, it is demonstrated that the combination of micropores and large mesopores is the main factor for an enhanced catalytic activity which is superior to that observed in other similar microporous activated carbon fibers. This provides an alternative way for the development of a new generation of catalytic material.

  12. Catalytic pyrolysis of oil fractions separated from food waste leachate over nanoporous acid catalysts.

    PubMed

    Kim, Seung-Soo; Heo, Hyeon Su; Kim, Sang Guk; Ryoo, Ryong; Kim, Jeongnam; Jeon, Jong-Ki; Park, Sung Hoon; Park, Young-Kwon

    2011-07-01

    Oil fractions, separated from food waste leachate, can be used as an energy source. Especially, high quality oil can be obtained by catalytic cracking. In this study, nanoporous catalysts such as Al-MCM-41 and mesoporous MFI type zeolite were applied to the catalytic cracking of oil fractions using the pyrolysis gas chromatography/mass spectrometry. Mesoporous MFI type zeolite showed better textural porosity than Al-MCM-41. In addition, mesoporous MFI type zeolite had strong Brönsted acidity while Al-MCM-41 had weak acidity. Significant amount of acid components in the food waste oil fractions were converted to mainly oxygenates and aromatics. As a result of its well-defined nanopores and strong acidity, the use of a mesoporous MFI type zeolite produced large amounts of gaseous and aromatic compounds. High yields of hydrocarbons within the gasoline range were also obtained in the case of mesoporous MFI type zeolite, whereas the use of Al-MCM-41, which exhibits relatively weak acidity, resulted in high yields of oxygenates and diesel range hydrocarbons.

  13. Nanoscale mapping of catalytic activity using tip-enhanced Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kumar, N.; Stephanidis, B.; Zenobi, R.; Wain, A. J.; Roy, D.

    2015-04-01

    Chemical mapping of a photocatalytic reaction with nanoscale spatial resolution is demonstrated for the first time using tip-enhanced Raman spectroscopy (TERS). An ultrathin alumina film applied to the Ag-coated TERS tip blocks catalytic interference whilst maintaining near-field electromagnetic enhancement, thus enabling spectroscopic imaging of catalytic activity on nanostructured Ag surfaces.

  14. Mutagenesis of putative catalytic and regulatory residues of Streptomyces chromofuscus phospholipase D differentially modifies phosphatase and phosphodiesterase activities.

    PubMed

    Zambonelli, Carlo; Casali, Monica; Roberts, Mary F

    2003-12-26

    Phospholipase D from Streptomyces chromofuscus (sc-PLD) is a member of the diverse family of metallo-phosphodiesterase/phosphatase enzymes that also includes purple acid phosphatases, protein phosphatases, and nucleotide phosphodiesterases. Whereas iron is an essential cofactor for scPLD activity, Mn2+ is also found in the enzyme. A third metal ion, Ca2+, has been shown to enhance scPLD catalytic activity although it is not an essential cofactor. Sequence alignment of scPLD with known phosphodiesterases and phosphatases requiring metal ions suggested that His-212, Glu-213, and Asp-389 could be involved in Mn2+ binding. H212A, E213A, and D389A were prepared to test this hypothesis. These three mutant enzymes and wild type scPLD show similar metal content but considerably different catalytic properties, suggesting different roles for each residue. His-212 appears involved in binding the phosphate group of substrates, whereas Glu-213 acts as a ligand for Ca2+. D389A showed a greatly reduced phosphodiesterase activity but almost unaltered ability to hydrolyze the phosphate group in p-nitrophenyl phosphate suggesting it had a critical role in aligning groups at the active site to control phosphodiesterase versus phosphatase activities. We propose a model for substrate and cofactor binding to the catalytic site of scPLD based on these results and on sequence alignment to purple acid phosphatases of known structure.

  15. Graphene incorporated, N doped activated carbon as catalytic electrode in redox active electrolyte mediated supercapacitor

    NASA Astrophysics Data System (ADS)

    Gao, Zhiyong; Liu, Xiao; Chang, Jiuli; Wu, Dapeng; Xu, Fang; Zhang, Lingcui; Du, Weimin; Jiang, Kai

    2017-01-01

    Graphene incorporated, N doped activated carbons (GNACs) are synthesized by alkali activation of graphene-polypyrrole composite (G-PPy) at different temperatures for application as electrode materials of supercapacitors. Under optimal activation temperature of 700 °C, the resultant samples, labeled as GNAC700, owns hierarchically porous texture with high specific surface area and efficient ions diffusion channels, N, O functionalized surface with apparent pseudocapacitance contribution and high wettability, thus can deliver a moderate capacitance, a high rate capability and a good cycleability when used as supercapacitor electrode. Additionally, the GNAC700 electrode demonstrates high catalytic activity for the redox reaction of pyrocatechol/o-quinone pair in H2SO4 electrolyte, thus enables a high pseudocapacitance from electrolyte. Under optimal pyrocatechol concentration in H2SO4 electrolyte, the electrode capacitance of GNAC700 increases by over 4 folds to 512 F g-1 at 1 A g-1, an excellent cycleability is also achieved simultaneously. Pyridinic- N is deemed to be responsible for the high catalytic activity. This work provides a promising strategy to ameliorate the capacitive performances of supercapacitors via the synergistic interaction between redox-active electrolyte and catalytic electrodes.

  16. Catalytic decomposition of hydrogen peroxide and 4-chlorophenol in the presence of modified activated carbons.

    PubMed

    Huang, Hsu-Hui; Lu, Ming-Chun; Chen, Jong-Nan; Lee, Cheng-Te

    2003-06-01

    The objective of this research was to examine the heterogeneous catalytic decomposition of H(2)O(2) and 4-chlorophenol (4-CP) in the presence of activated carbons modified with chemical pretreatments. The decomposition of H(2)O(2) was suppressed significantly by the change of surface properties including the decreased pH(pzc) modified with oxidizing agent and the reduced active sites occupied by the adsorption of 4-CP. The apparent reaction rate of H(2)O(2) decomposition was dominated by the intrinsic reaction rates on the surface of activated carbon rather than the mass transfer rate of H(2)O(2) to the solid surface. By the detection of chloride ion in suspension, the reduction of 4-CP was not only attributed to the advanced adsorption but also the degradation of 4-CP. The catalytic activity toward 4-CP for the activated carbon followed the inverse sequence of the activity toward H(2)O(2), suggesting that acidic surface functional group could retard the H(2)O(2) loss and reduce the effect of surface scavenging resulting in the increase of the 4-CP degradation efficiency. Few effective radicals were expected to react with 4-CP for the strong effect of surface scavenging, which could explain why the degradation rate of 4-CP observed in this study was so slow and the dechlorination efficiency was independent of the 4-CP concentration in aqueous phase. Results show that the combination of H(2)O(2) and granular activated carbon (GAC) did increase the total removal of 4-CP than that by single GAC adsorption.

  17. 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

  18. Fourier Transform Infrared (FTIR) Observation Of Catalytically Active Intermediates Produced By Laser Photolysis Of Iron Pentacarbonyl

    NASA Astrophysics Data System (ADS)

    Paquette, Michael S.

    1984-05-01

    The pulsed laser excitation of iron pentacarbonyl in solutions of 1-pentene photoinitiates a highly active catalytic process for isomerization of the olefin. This process is observed in situ by rapid scanning FTIR spectroscopy, allowing subsecond acquisition of spectra. These are deconvoluted into discrete spectral components which are assigned molecular formulas. Specific activities have been obtained for two catalytically significant complexes from a correlation of catalytic activity with compositional changes. A similar interpretation of multipulse and cw experiments allowed development of a comprehensive cycle of thermal and photochemical interconversions among components.

  19. 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.

  20. Expression of catalytically active recombinant Helicobacter pylori urease at wild-type levels in Escherichia coli.

    PubMed Central

    Hu, L T; Mobley, H L

    1993-01-01

    The genes encoding Helicobacter pylori urease, a nickel metalloenzyme, have been cloned and expressed in Escherichia coli. Enzymatic activity, however, has been very weak compared with that in clinical isolates of H. pylori. Conditions under which near wild-type urease activity was achieved were developed. E. coli. SE5000 containing recombinant H. pylori urease genes was grown in minimal medium containing no amino acids, NiCl2 was added to 0.75 microM, and structural genes ureA and ureB (pHP902) were overexpressed in trans to the complete urease gene cluster (pHP808). Under these conditions, E. coli SE5000 pHP808/pHP902) expressed a urease activity up to 87 mumol of urea per min per mg of protein (87 U/mg of protein), a level approaching that of wild-type H. pylori UMAB41 (100 U/mg of protein), from which the genes were cloned. Poor catalytic activity of recombinant clones grown in Luria broth or M9 medium containing 0.5% Casamino Acids was due to chelation of nickel ions by medium components, particularly histidine and cysteine. In cultures containing these amino acids, 63Ni2+ was prevented from being transported into cells and was not incorporated into urease protein. As a consequence, M9 minimal medium cultures containing histidine or cysteine produced only 0.05 and 0.9%, respectively, of active urease produced by control cultures containing no amino acids. We conclude that recombinant H. pylori urease is optimally expressed when Ni2+ transport is not inhibited and when sufficient synthesis of urease subunits UreA and UreB is provided. Images PMID:8500893

  1. New Ulvan-Degrading Polysaccharide Lyase Family: Structure and Catalytic Mechanism Suggests Convergent Evolution of Active Site Architecture.

    PubMed

    Ulaganathan, ThirumalaiSelvi; Boniecki, Michal T; Foran, Elizabeth; Buravenkov, Vitaliy; Mizrachi, Naama; Banin, Ehud; Helbert, William; Cygler, Miroslaw

    2017-03-23

    Ulvan is a complex sulfated polysaccharide biosynthesized by green seaweed and contains predominantly rhamnose, xylose, and uronic acid sugars. Ulvan-degrading enzymes have only recently been identified and added to the CAZy ( www.cazy.org ) database as family PL24, but neither their structure nor catalytic mechanism(s) are yet known. Several homologous, new ulvan lyases, have been discovered in Pseudoalteromonas sp. strain PLSV, Alteromonas LOR, and Nonlabens ulvanivorans, defining a new family PL25, with the lyase encoded by the gene PLSV_3936 being one of them. This enzyme cleaves the glycosidic bond between 3-sulfated rhamnose (R3S) and glucuronic acid (GlcA) or iduronic acid (IdoA) via a β-elimination mechanism. We report the crystal structure of PLSV_3936 and its complex with a tetrasaccharide substrate. PLSV_3936 folds into a seven-bladed β-propeller, with each blade consisting of four antiparallel β-strands. Sequence conservation analysis identified a highly conserved region lining at one end of a deep crevice on the protein surface. The putative active site was identified by mutagenesis and activity measurements. Crystal structure of the enzyme with a bound tetrasaccharide substrate confirmed the identity of base and acid residues and allowed determination of the catalytic mechanism and also the identification of residues neutralizing the uronic acid carboxylic group. The PLSV_3936 structure provides an example of a convergent evolution among polysaccharide lyases toward a common active site architecture embedded in distinct folds.

  2. Effects of FGFR2 kinase activation loop dynamics on catalytic activity.

    PubMed

    Karp, Jerome M; Sparks, Samuel; Cowburn, David

    2017-02-01

    The structural mechanisms by which receptor tyrosine kinases (RTKs) regulate catalytic activity are diverse and often based on subtle changes in conformational dynamics. The regulatory mechanism of one such RTK, fibroblast growth factor receptor 2 (FGFR2) kinase, is still unknown, as the numerous crystal structures of the unphosphorylated and phosphorylated forms of the kinase domains show no apparent structural change that could explain how phosphorylation could enable catalytic activity. In this study, we use several enhanced sampling molecular dynamics (MD) methods to elucidate the structural changes to the kinase's activation loop that occur upon phosphorylation. We show that phosphorylation favors inward motion of Arg664, while simultaneously favoring outward motion of Leu665 and Pro666. The latter structural change enables the substrate to bind leading to its resultant phosphorylation. Inward motion of Arg664 allows it to interact with the γ-phosphate of ATP as well as the substrate tyrosine. We show that this stabilizes the tyrosine and primes it for the catalytic phosphotransfer, and it may lower the activation barrier of the phosphotransfer reaction. Our work demonstrates the value of including dynamic information gleaned from computer simulation in deciphering RTK regulatory function.

  3. Effects of FGFR2 kinase activation loop dynamics on catalytic activity

    PubMed Central

    2017-01-01

    The structural mechanisms by which receptor tyrosine kinases (RTKs) regulate catalytic activity are diverse and often based on subtle changes in conformational dynamics. The regulatory mechanism of one such RTK, fibroblast growth factor receptor 2 (FGFR2) kinase, is still unknown, as the numerous crystal structures of the unphosphorylated and phosphorylated forms of the kinase domains show no apparent structural change that could explain how phosphorylation could enable catalytic activity. In this study, we use several enhanced sampling molecular dynamics (MD) methods to elucidate the structural changes to the kinase’s activation loop that occur upon phosphorylation. We show that phosphorylation favors inward motion of Arg664, while simultaneously favoring outward motion of Leu665 and Pro666. The latter structural change enables the substrate to bind leading to its resultant phosphorylation. Inward motion of Arg664 allows it to interact with the γ-phosphate of ATP as well as the substrate tyrosine. We show that this stabilizes the tyrosine and primes it for the catalytic phosphotransfer, and it may lower the activation barrier of the phosphotransfer reaction. Our work demonstrates the value of including dynamic information gleaned from computer simulation in deciphering RTK regulatory function. PMID:28151998

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

    PubMed

    Zayed, Mervat F; Eisa, Wael H

    2014-01-01

    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.

  5. 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.

  6. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

    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.

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

    PubMed

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

    2016-10-19

    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.

  9. 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.

  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. All the catalytic active sites of MoS2 for hydrogen evolution

    DOE PAGES

    Li, Guoqing; Zhang, Du; Qiao, Qiao; ...

    2016-11-29

    MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. Here, the intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5more » s–1 (65–75 mV/dec), 3.2 s–1 (65–85 mV/dec), and 0.1 s–1 (120–160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7–10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies.« less

  12. 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.

  13. Determination of the positions of aluminum atoms introduced into SSZ-35 and the catalytic properties of the generated Brønsted acid sites.

    PubMed

    Miyaji, Akimitsu; Kimura, Nobuhiro; Shiga, Akinobu; Hayashi, Yoshihiro; Nishitoba, Toshiki; Motokura, Ken; Baba, Toshihide

    2017-03-01

    The positions of aluminum (Al) atoms in SSZ-35 together with the characteristics of the generated protons were investigated by (27)Al multiple quantum magic-angle spinning (MQ-MAS), (29)Si MAS, and (1)H MAS NMR data analyses accompanied by a variable temperature (1)H MAS NMR analysis. The origin of the acidic -OH groups (Brønsted acid sites) generated by introducing Al atoms into the T sites was investigated and the T sites introduced into the Al atoms were revealed. To further determine the catalytic properties of the acidic protons generated in SSZ-35, the influence of the concentration of the Al atoms on the catalytic activity and selectivity during the transformation of toluene was examined.

  14. Production of aviation fuel via catalytic hydrothermal decarboxylation of fatty acids in microalgae oil.

    PubMed

    Yang, Cuiyue; Nie, Renfeng; Fu, Jie; Hou, Zhaoyin; Lu, Xiuyang

    2013-10-01

    A series of fatty acids in microalgae oil, such as stearic acid, palmitic acid, lauric acid, myristic acid, arachidic acid and behenic acid, were selected as the raw materials to produce aviation fuel via hydrothermal decarboxylation over a multi-wall carbon nanotube supported Pt catalyst (Pt/MWCNTs). It was found that Pt/MWCNTs catalysts exhibited higher activity for the hydrothermal decarboxylation of stearic acid with a 97% selectivity toward heptadecane compared to Pt/C and Ru/C under the same conditions. And Pt/MWCNTs is also capable for the decarboxylation of different fatty acids in microalgae oil. The reaction conditions, such as Pt/MWCNTs loading amount, reaction temperature and time were optimized. The activation energy of stearic acid decarboxylation over Pt/MWCNTs was calculated (114 kJ/mol).

  15. Removal of salicylic acid on perovskite-type oxide LaFeO3 catalyst in catalytic wet air oxidation process.

    PubMed

    Yang, Min; Xu, Aihua; Du, Hongzhang; Sun, Chenglin; Li, Can

    2007-01-02

    It has been found that salicylic acid can be removal effectively at the lower temperature of 140 degrees C on perovskite-type oxide LaFeO3 catalyst in the catalytic wet air oxidation (CWAO) process. Under the same condition, the activities for the CWAO of phenol, benzoic acid and sulfonic salicylic acid have been also investigated. The results indicated that, with compared to the very poor activities for phenol and benzoic acid, the activities for salicylic acid and sulfonic salicylic acid were very high, which are attributed to their same intramolecular H-bonding structures. With the role of hard acidity of intramolecular H-bonding, salicylic acid and sulfonic salicylic acid can be adsorbed effectively on the basic center of LaFeO3 catalyst and are easy to take place the total oxidation reaction. However, at temperatures higher than 140 degrees C, the intramolecular H-bonding structure of salicylic acid was destroyed and the activities at 160 and 180 degrees C decreased greatly, which confirms further the key role of intramolecular H-bonding in the CWAO. Moreover, the LaFeO3 catalyst also indicated a superior stability of activity and structure in CWAO of salicylic acid.

  16. Partial deficit of pantothenate kinase 2 catalytic activity in a case of tremor-predominant neurodegeneration with brain iron accumulation.

    PubMed

    Liang, Tsao-Wei; Truax, Adam C; Trojanowski, John Q; Lee, Virginia M-Y; Stern, Matthew B; Kotzbauer, Paul T

    2006-05-01

    We describe an atypical case of pantothenate kinase-associated neurodegeneration (PKAN) in which slowly progressive arm tremor was the predominant symptom beginning at the age of 25, with late-onset dystonia and dysarthria developing at the age of 50. Compound heterozygous mutations resulting in missense amino acid substitutions G521R and I529V were identified in the pantothenate kinase (PANK2) gene. We demonstrate that while the G521R mutation results in an unstable and inactive protein, the previously unreported I529V substitution has no apparent effect on the stability or catalytic activity of PanK2. The phenotype that results from this combination of mutations suggests that atypical presentations of PKAN may arise from partial deficits in PanK2 catalytic activity.

  17. 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.

  18. 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.

  19. Lipase immobilized catalytically active membrane for synthesis of lauryl stearate in a pervaporation membrane reactor.

    PubMed

    Zhang, Weidong; Qing, Weihua; Ren, Zhongqi; Li, Wei; Chen, Jiangrong

    2014-11-01

    A composite catalytically active membrane immobilized with Candida rugosa lipase has been prepared by immersion phase inversion technique for enzymatic synthesis of lauryl stearate in a pervaporation membrane reactor. SEM images showed that a "sandwich-like" membrane structure with a porous lipase-PVA catalytic layer uniformly coated on a polyvinyl alcohol (PVA)/polyethersulfone (PES) bilayer was obtained. Optimum conditions for lipase immobilization in the catalytic layer were determined. The membrane was proved to exhibit superior thermal stability, pH stability and reusability than free lipase under similar conditions. In the case of pervaporation coupled synthesis of lauryl stearate, benefited from in-situ water removal by the membrane, a conversion enhancement of approximately 40% was achieved in comparison to the equilibrium conversion obtained in batch reactors. In addition to conversion enhancement, it was also found that excess water removal by the catalytically active membrane appears to improve activity of the lipase immobilized.

  20. 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

  1. Effect of oxidation and catalytic reduction of trace organic contaminants on their activated carbon adsorption.

    PubMed

    Schoutteten, Klaas V K M; Hennebel, Tom; Dheere, Ellen; Bertelkamp, Cheryl; De Ridder, David J; Maes, Synthia; Chys, Michael; Van Hulle, Stijn W H; Vanden Bussche, Julie; Vanhaecke, Lynn; Verliefde, Arne R D

    2016-12-01

    The combination of ozonation and activated carbon (AC) adsorption is an established technology for removal of trace organic contaminants (TrOCs). In contrast to oxidation, reduction of TrOCs has recently gained attention as well, however less attention has gone to the combination of reduction with AC adsorption. In addition, no literature has compared the removal behavior of reduction vs. ozonation by-products by AC. In this study, the effect of pre-ozonation vs pre-catalytic reduction on the AC adsorption efficiency of five TrOCs and their by-products was compared. All compounds were susceptible to oxidation and reduction, however the catalytic reductive treatment proved to be a slower reaction than ozonation. New oxidation products were identified for dinoseb and new reduction products were identified for carbamazepine, bromoxynil and dinoseb. In terms of compatibility with AC adsorption, the influence of the oxidative and reductive pretreatments proved to be compound dependent. Oxidation products of bromoxynil and diatrizoic acid adsorbed better than their parent TrOCs, but oxidation products of atrazine, carbamazepine and dinoseb showed a decreased adsorption. The reductive pre-treatment showed an enhanced AC adsorption for dinoseb and a major enhancement for diatrizoic acid. For atrazine and bromoxynil, no clear influence on adsorption was noted, while for carbamazepine, the reductive pretreatment resulted in a decreased AC affinity. It may thus be concluded that when targeting mixtures of TrOCs, a trade-off will undoubtedly have to be made towards overall reactivity and removal of the different constituents, since no single treatment proves to be superior to the other.

  2. Enhancement of ribozyme catalytic activity by a contiguous oligodeoxynucleotide (facilitator) and by 2'-O-methylation.

    PubMed Central

    Goodchild, J

    1992-01-01

    RNA catalysts (ribozymes) designed to cleave sequences unique to viral RNA's might be developed as therapeutics. For this purpose, they would require high catalytic efficiency and resistance to nucleases. Reported here are two approaches that can be used in combination to improve these properties. First, catalytic efficiency can be improved by oligonucleotides (facilitators) that bind to the substrate contiguously with the 3'-end of the ribozyme. Second, 2'-O-methylation of flanking sequences of the ribozyme increases catalytic activity as well as resistance to nucleases. In combination with a facilitator oligodeoxynucleotide, the cleavage rate was increased 20 fold over that of the unmodified ribozyme. Images PMID:1383929

  3. 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.

  4. 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.

  5. Layered materials with coexisting acidic and basic sites for catalytic one-pot reaction sequences.

    PubMed

    Motokura, Ken; Tada, Mizuki; Iwasawa, Yasuhiro

    2009-06-17

    Acidic montmorillonite-immobilized primary amines (H-mont-NH(2)) were found to be excellent acid-base bifunctional catalysts for one-pot reaction sequences, which are the first materials with coexisting acid and base sites active for acid-base tamdem reactions. For example, tandem deacetalization-Knoevenagel condensation proceeded successfully with the H-mont-NH(2), affording the corresponding condensation product in a quantitative yield. The acidity of the H-mont-NH(2) was strongly influenced by the preparation solvent, and the base-catalyzed reactions were enhanced by interlayer acid sites.

  6. Development of catalytically active and highly stable catalyst supports for polymer electrolyte membrane fuel cells

    NASA Astrophysics Data System (ADS)

    Kim, Taekeun; Xie, Tianyuan; Jung, Wonsuk; Gadala-Maria, Francis; Ganesan, Prabhu; Popov, Branko N.

    2015-01-01

    Novel procedures are developed for the synthesis of highly stable carbon composite catalyst supports (CCCS-800 °C and CCCS-1100 °C) and an activated carbon composite catalyst support (A-CCCS). These supports are synthesized through: (i) surface modification with acids and inclusion of oxygen groups, (ii) metal-catalyzed pyrolysis, and (iii) chemical leaching to remove excess metal used to dope the support. The procedure results in increasing carbon graphitization and inclusion of non-metallic active sites on the support surface. Catalytic activity of CCCS indicates an onset potential of 0.86 V for the oxygen reduction reaction (ORR) with well-defined kinetic and mass-transfer regions and ∼2.5% H2O2 production in rotating ring disk electrode (RRDE) studies. Support stability studies at 1.2 V constant potential holding for 400 h indicate high stability for the 30% Pt/A-CCCS catalyst with a cell potential loss of 27 mV at 800 mA cm-2 under H2-air, 32% mass activity loss, and 30% ECSA loss. Performance evaluation in polymer electrolyte membrane (PEM) fuel cell shows power densities (rated) of 0.18 and 0.23 gPt kW-1 for the 30% Pt/A-CCCS and 30% Pt/CCCS-800 °C catalysts, respectively. The stabilities of various supports developed in this study are compared with those of a commercial Pt/C catalyst.

  7. 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.

  8. 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.

  9. Selection of active phase of MnO2 for catalytic ozonation of 4-nitrophenol.

    PubMed

    Nawaz, Faheem; Cao, Hongbin; Xie, Yongbing; Xiao, Jiadong; Chen, Yue; Ghazi, Zahid Ali

    2017-02-01

    Catalytic ozonation is a highly effective method in wastewater treatment, and MnO2 materials are widely recognized as active heterogeneous catalysts in this process. Many works reported the progress in active MnO2 synthesis, but the active phase is rarely systematically studied. In this paper, all six phases of MnO2 (α-, β-, δ-, γ-, λ- and ε-) were synthesized by facile methods. Their catalytic activities in ozonation of 4-nitrophenol (4-NP) were evaluated and correlated with the physicochemical properties obtained from X-ray Diffraction (XRD), transmission electron microscopy (TEM), physical adsorption and cyclic voltammetry (CV) analysis. α- MnO2 was found to be the most active catalyst in 4-NP degradation at neutral pH. MnO2 with low average oxidation state (AOS) showed stronger oxidation/reduction peaks in CV characterization, which benefited catalytic decomposition of ozone to generate active species. Superoxide radical was confirmed as the main oxidizing species, along with singlet oxygen and ozone molecule oxidation in bulk solution and little contribution of oxidation on the MnO2 surface. Mn(2+) leaching happened during catalytic ozonation, but its catalytic role is negligible. This result may give rise to the preparation of new active MnO2 catalysts.

  10. 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.

  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. 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

  13. 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

  14. Antitumour, antimicrobial and catalytic activity of gold nanoparticles synthesized by different pH propolis extracts

    NASA Astrophysics Data System (ADS)

    Gatea, Florentina; Teodor, Eugenia Dumitra; Seciu, Ana-Maria; Covaci, Ovidiu Ilie; Mănoiu, Sorin; Lazăr, Veronica; Radu, Gabriel Lucian

    2015-07-01

    The Romanian propolis was extracted in five different media, respectively, in water (pH 6.8), glycine buffer (pH 2.5), acetate buffer (pH 5), phosphate buffer (pH 7.4) and carbonate buffer (pH 9.2). The extracts presented different amounts of flavonoids and phenolic acids, increasing pH leading to higher concentrations of active compounds. Five variants of gold nanoparticles suspensions based on different pH Romanian propolis aqueous extracts were successfully synthesized. The obtained nanoparticles presented dimensions between 20 and 60 nm in dispersion form and around 18 nm in dried form, and different morphologies (spherical, hexagonal, triangular). Fourier transform infrared spectroscopy proved the attachment of organic compounds from propolis extracts to the colloidal gold suspensions and X-ray diffraction certified that the suspensions contain metallic gold. The obtained propolis gold nanoparticles do not exhibit any antibacterial or antifungal activity, but presented different catalytic activities and toxicity on tumour cells.

  15. 3D Flower-like β-MnO2/Reduced Graphene Oxide Nanocomposites for Catalytic Ozonation of Dichloroacetic Acid

    PubMed Central

    Li, Gang; Li, Kezheng; Liu, Aijuan; Yang, Ping; Du, Yukou; Zhu, Mingshan

    2017-01-01

    Considering the potential use of manganese oxide based nanocomposite in catalytic ozonation of water contaminant, we report unique three-dimensional (3D) nanoarchitectures composed of β-MnO2 and reduced graphene oxide (RGO) for catalytic ozonation of dichloroacetic acid (DCAA) from drinking water. The catalytic results show that the 3D β-MnO2/RGO nanocomposites (FMOG) can be used as efficient and stable ozonation catalysts to eliminate DCAA from water. The probable mechanism of catalytic ozonation was also proposed by detecting intermediates using gas chromatography-mass spectrometry. This result likely paves a facile avenue and initiates new opportunities for the exploration of heterogeneous catalysts for the removal of disinfection by-products from drinking water.

  16. 3D Flower-like β-MnO2/Reduced Graphene Oxide Nanocomposites for Catalytic Ozonation of Dichloroacetic Acid

    NASA Astrophysics Data System (ADS)

    Li, Gang; Li, Kezheng; Liu, Aijuan; Yang, Ping; Du, Yukou; Zhu, Mingshan

    2017-03-01

    Considering the potential use of manganese oxide based nanocomposite in catalytic ozonation of water contaminant, we report unique three-dimensional (3D) nanoarchitectures composed of β-MnO2 and reduced graphene oxide (RGO) for catalytic ozonation of dichloroacetic acid (DCAA) from drinking water. The catalytic results show that the 3D β-MnO2/RGO nanocomposites (FMOG) can be used as efficient and stable ozonation catalysts to eliminate DCAA from water. The probable mechanism of catalytic ozonation was also proposed by detecting intermediates using gas chromatography-mass spectrometry. This result likely paves a facile avenue and initiates new opportunities for the exploration of heterogeneous catalysts for the removal of disinfection by-products from drinking water.

  17. Modulation of Tumorigenesis by Dietary Intervention Is Not Mediated by SIRT1 Catalytic Activity

    PubMed Central

    Clark-Knowles, Katherine V.; Dewar-Darch, Danielle; Jardine, Karen E.; McBurney, Michael W.

    2014-01-01

    The protein deacetylase SIRT1 is involved in the regulation of a large number of cellular processes that are thought to be required for cancer initiation and progression. Both SIRT1 activity and tumorigenesis can be influenced by dietary fat and polyphenolics. We set out to determine whether dietary modulations of tumorigenesis are mediated by SIRT1 catalytic functions. We introduced a mammary gland tumor-inducing transgene, MMTV-PyMT, into stocks of mice bearing a H355Y point mutation in the Sirt1 gene that abolishes SIRT1 catalytic activity. Tumor latency was reduced in animals fed a high fat diet but this effect was not dependent on SIRT1 activity. Resveratrol had little effect on tumor formation except in animals heterozygous for the mutant Sirt1 gene. We conclude that the effects of these dietary interventions on tumorigenesis are not mediated by modulation of SIRT1 catalytic activity. PMID:25380034

  18. Removal performance and mechanism of ibuprofen from water by catalytic ozonation using sludge-corncob activated carbon as catalyst.

    PubMed

    Wang, Hongjuan; Zhang, Liqiu; Qi, Fei; Wang, Xue; Li, Lu; Feng, Li

    2014-09-01

    To discover the catalytic activity of sludge-corncob activated carbon in catalytic ozonation of Ibuprofen, the performance of sludge-corncob activated carbon and three selected commercial activated carbons as catalysts in catalytic ozonation was investigated. The observation indicates the degradation rate of Ibuprofen increases significantly in the presence of sludge-corncob activated carbon and the catalytic activity of sludge-corncob activated carbon is much higher than that of the other three commercial activated carbons. Ibuprofen's removal rate follows pseudo-first order kinetics model well. It is also found that the adsorption removal of Ibuprofen by sludge-corncob activated carbon is less than 30% after 40 min. And the removal efficiency of Ibuprofen in the hybrid ozone/sludge-corncob activated carbon system is higher than the sum of sludge-corncob activated carbon adsorption and ozonation alone, which is a supportive evidence for catalytic reaction. In addition, the results of radical scavenger experiments demonstrate that catalytic ozonation of Ibuprofen by sludge-corncob activated carbon follows a hydroxyl radical reaction pathway. During ozonation of Ibuprofen in the presence of activated carbon, ozone could be catalytically decomposed to form hydrogen peroxide, which can promote the formation of hydroxyl radical. The maximum amount of hydrogen peroxide occurs in the presence of sludge-corncob activated carbon, which can explain why sludge-corncob activated carbon has the best catalytic activity among four different activated carbons.

  19. Influence of surface modification on catalytic activity of activated carbon toward decomposition of hydrogen peroxide and 2-chlorophenol.

    PubMed

    Huang, Hsu-Hui; Lu, Ming-Chun; Chen, Jong-Nan; Lee, Cheng-Te

    2003-07-01

    The objective of this research was to investigate the influence of the activated carbons modified by chemical treatment on the surface catalyzed loss of H2O2 and 2-CP. The characteristics of the modified activated carbons were examined by several techniques including nitrogen adsorption, SEM, and EDS. The H2O2 decomposition rate would be suppressed significantly either by the change of surface properties modified with chemical treatment or the reduction of active sites occupied with the adsorption of 2-CP. In addition, the H2O2 decomposition rate with activated carbons within a specific time can be described by a second-order kinetic expression with respect to the concentration of GAC and H2O2 in the absence or presence of 2-CP. The catalytic activities of the three activated carbons toward 2-CP reduction followed the inverse sequence of those toward H2O2 loss, implying that acidic surface functional group could retard the H2O2 loss and reduce the effect of surface scavenging resulting in increasing the reduction efficiency of 2-CP. By the detection of chloride ions in reaction mixture, it can be demonstrated that the reduction of 2-CP was not only attributed to the advanced adsorption but also the oxidation of the 2-CP with effective radicals. The real oxidation efficiency of 2-CP for the activated carbon modified with hot nitric acid was observed between 0.04 and 0.01 (mol/mol), offering a comparable efficiency to that of the other oxidation system using metal oxide as catalyst.

  20. Structural, morphological and catalytic characterization of neutral Ag salt of 12-tungstophosphoric acid: Influence of preparation conditions

    NASA Astrophysics Data System (ADS)

    Holclajtner-Antunović, Ivanka; Bajuk-Bogdanović, Danica; Popa, Alexandru; Nedić Vasiljević, Bojana; Krstić, Jugoslav; Mentus, Slavko; Uskoković-Marković, Snežana

    2015-02-01

    The objective of this study is the structural and morphological characterization of the Ag3PW12O40 salts (AgWPA) of 12-tungstophosphoric acid (WPA) obtained under different preparation conditions and testing of their acid catalytic activity in dehydration of ethanol. The structure, morphology and physicochemical characteristics were determined by Fourier transform infrared (FT-IR) and Raman spectroscopy, X-ray diffraction (XRD), nitrogen physisorption at -196 °C, scanning electron microscopy (SEM) and differential thermal (DTA) and thermogravimetric analysis (TGA). It is shown that the preparation process has a significant influence on the morphological properties of the obtained materials which may be explained by the supposed mechanism of the formation of nanocrystallite‧s aggregates with more or less epitaxial connection. Neutral AgWPA obtained by filtration from supernatant forms porous aggregates of a symmetric dodecahedral shape, having average sizes about 2 μm. This sample shows higher specific area in comparison with the salt obtained by evaporation due to the higher micropore volume, while mesopore volumes are the same for both salts. Thus conversion of ethanol and selectivities of the main products, ethylene and diethyl ether, are almost the same and constant for both prepared salts, while their values are changed over the reaction time for the parent WPA acid.

  1. A spectroscopic and catalytic investigation of active phase-support interactions

    SciTech Connect

    Haller, G.L.

    1991-01-01

    Active catalytic phases (metal, mixed metals, oxide or mixed oxides) interacting with oxide support on which the active phase is dispersed can affect the percentage exposed, the morphology of supported particles, the degree of reducibility of cations, etc., in a variety of ways. Our objective is to characterize the physical chemistry of the active phase-oxide support by spectroscopic methods and to correlate this structure with catalytic function. The three systems discussed in this progress report are Ag/TiO{sub 2}, Ru-Cu/SiO{sub 2} and SiO{sub 2}/Al{sub 2}O{sub 3}. 24 refs., 3 figs., 2 tabs.

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

    PubMed

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

    2013-06-05

    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.

  3. Catalytic activity of titania zirconia mixed oxide catalyst for dimerization eugenol

    NASA Astrophysics Data System (ADS)

    Tursiloadi, S.; Kristiani, A.; Jenie, S. N. Aisyiyah; Laksmono, J. A.

    2017-01-01

    Clove oil has been found to possess antibacterial, antifungal, antiviral, antitumor, antioxidant and insecticidal properties. The major compound of clove oil is eugenol about 49-87%. Eugenol as phenolic compounds exhibits antioxidant and antimicrobial activities. The derivative compound of eugenol, dieugenol, show antioxidant potency better than parent eugenol. A series of TiO2-ZrO2 mixed oxides (TZ) with various titanium contents from 0 to 100wt%, prepared by using sol gel method were tested their catalytic activity for dimerization eugenol, Their catalytic activity show that these catalysts resulted a low yield of dimer eugenol, dieugenol, about 2-9 % and the purity is more than 50%.

  4. All the catalytic active sites of MoS2 for hydrogen evolution

    SciTech Connect

    Li, Guoqing; Zhang, Du; Qiao, Qiao; Yu, Yifei; Peterson, David; Zafar, Abdullah; Kumar, Raj; Curtarolo, Stefano; Hunte, Frank; Shannon, Steve; Zhu, Yimei; Yang, Weitao; Cao, Linyou

    2016-11-29

    MoS2 presents a promising low-cost catalyst for the hydrogen evolution reaction (HER), but the understanding about its active sites has remained limited. Here we present an unambiguous study of the catalytic activities of all possible reaction sites of MoS2, including edge sites, sulfur vacancies, and grain boundaries. We demonstrate that, in addition to the well-known catalytically active edge sites, sulfur vacancies provide another major active site for the HER, while the catalytic activity of grain boundaries is much weaker. Here, the intrinsic turnover frequencies (Tafel slopes) of the edge sites, sulfur vacancies, and grain boundaries are estimated to be 7.5 s–1 (65–75 mV/dec), 3.2 s–1 (65–85 mV/dec), and 0.1 s–1 (120–160 mV/dec), respectively. We also demonstrate that the catalytic activity of sulfur vacancies strongly depends on the density of the vacancies and the local crystalline structure in proximity to the vacancies. Unlike edge sites, whose catalytic activity linearly depends on the length, sulfur vacancies show optimal catalytic activities when the vacancy density is in the range of 7–10%, and the number of sulfur vacancies in high crystalline quality MoS2 is higher than that in low crystalline quality MoS2, which may be related with the proximity of different local crystalline structures to the vacancies.

  5. Kinetic spectrophotometric method for the determination of oxalic acid by its catalytic effect on the oxidation of safranine by dichromate

    NASA Astrophysics Data System (ADS)

    Ensafi, Ali A.; Abbasi, S.; Rezaei, B.

    2001-08-01

    A new catalytic kinetic spectrophotometric method for the determination of oxalic acid has been described based on its catalytic effect on the redox reaction between safranine and dichromate in dilute sulfuric acid media. The reaction is monitored photometrically by measuring the decrease in absorbance of safranine at the maximum wavelength of 530 nm. Under the optimum conditions, a calibration graph from 0.10 to 10.00 μg ml -1 of oxalic acid with a detection limit of 0.08 μg ml -1 was obtained. The relative standard deviation (R.S.D.) for ten replicate measurements of 1.0 and 5.0 μg ml -1 oxalic acid was 2.7 and 2.5%, respectively. The purposed method is simple, sensitive, selective and inexpensive. The applicability of the proposed method was determined by the determination of oxalic acid in spinach and wastewater samples with satisfactory results.

  6. Kinetic spectrophotometric method for the determination of oxalic acid by its catalytic effect on the oxidation of safranine by dichromate.

    PubMed

    Ensafi, A A; Abbasi, S; Rezaei, B

    2001-08-01

    A new catalytic kinetic spectrophotometric method for the determination of oxalic acid has been described based on its catalytic effect on the redox reaction between safranine and dichromate in dilute sulfuric acid media. The reaction is monitored photometrically by measuring the decrease in absorbance of safranine at the maximum wavelength of 530 nm. Under the optimum conditions, a calibration graph from 0.10 to 10.00 microg ml(-1) of oxalic acid with a detection limit of 0.08 microg ml(-1) was obtained. The relative standard deviation (R.S.D.) for ten replicate measurements of 1.0 and 5.0 microg ml(-1) oxalic acid was 2.7 and 2.5%, respectively. The purposed method is simple, sensitive, selective and inexpensive. The applicability of the proposed method was determined by the determination of oxalic acid in spinach and wastewater samples with satisfactory results.

  7. 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.

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

    PubMed

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

    2014-10-21

    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˙(-)) and singlet oxygen ((1)O2) 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 ˙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˙(-) under neutral conditions, but not under acidic conditions. The (1)O2 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.

  9. 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.

  10. Determination of tertiary amines and salts of organic acids in acetic acid by catalytic thermometric titration.

    PubMed

    Vajgand, V J; Gaál, F F

    1967-03-01

    A new method of determination of tertiary amines and salts of organic adds in acetic acid solution, to which about 2 % of water and 8% acetic anhydride are added, is described. After the equivalence point, the excess of perchloric acid catalyses the exothermic reaction of water with acetic anhydride. The end-point is determined from the graph of temperature against volume of added titrant. If a slightly soluble compound is produced during the titration, the precision of the new method is superior to that of the potentiometric method.

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

    PubMed

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

    2016-04-15

    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.

  12. 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

  13. 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.

  14. Catalase-like and peroxidase-like catalytic activities of silicon nanowire arrays.

    PubMed

    Wang, Hongwei; Jiang, Wenwen; Wang, Yanwei; Liu, Xiaoli; Yao, Jianlin; Yuan, Lin; Wu, Zhaoqiang; Li, Dan; Song, Bo; Chen, Hong

    2013-01-08

    Silicon nanowire arrays (SiNWAs) were found to have catalytic activities similar to those of biological enzymes catalase and peroxidase. Thus not only can these materials catalyze the decomposition reaction of H(2)O(2) into water and oxygen, but they can also catalyze the oxidation of o-phenylenediamine (OPD), a common substrate for peroxidases, by H(2)O(2). The presence of Si-H bonds and the morphology of the SiNWAs are found to be crucial to the occurrence of such catalytic activity. When the SiNWAs are reacted with H(2)O(2), the data from Raman spectroscopy suggests the formation of (Si-H)(2)···(O species) ((Si-H)(2)···Os), which is presumably responsible for the catalytic activity. These findings suggest the potential use of SiNWAs as enzyme mimics in medicine, biotechnology, and environmental chemistry.

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

    PubMed

    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.

  16. 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

  17. Increasing thermal stability and catalytic activity of glutamate decarboxylase in E. coli: An in silico study.

    PubMed

    Tavakoli, Yasaman; Esmaeili, Abolghasem; Saber, Hossein

    2016-10-01

    Glutamate decarboxylase (GAD) is an enzyme that converts l-glutamate to gamma amino butyric acid (GABA) that is a widely used drug to treat mental disorders like Alzheimer's disease. In this study for the first time point mutation was performed virtually in the active site of the E. coli GAD in order to increase thermal stability and catalytic activity of the enzyme. Energy minimization and addition of water box were performed using GROMACS 5.4.6 package. PoPMuSiC 2.1 web server was used to predict potential spots for point mutation and Modeller software was used to perform point mutation on three dimensional model. Molegro virtual docker software was used for cavity detection and stimulated docking study. Results indicate that performing mutation separately at positions 164, 302, 304, 393, 396, 398 and 410 increase binding affinity to substrate. The enzyme is predicted to be more thermo- stable in all 7 mutants based on ΔΔG value.

  18. A comparative study of the surface structure, acidity, and catalytic performance of tungstated zirconia prepared from crystalline zirconia or amorphous zirconium oxyhydroxide.

    PubMed

    Lebarbier, Vanessa; Clet, Guillaume; Houalla, Marwan

    2006-07-20

    Tungstated zirconias prepared from W deposition on zirconium oxyhydroxide are reportedly active for alkane isomerization, whereas solids synthesized by impregnation of zirconia are inactive. The origin of the differences between the two preparations is not fully understood. The present paper examines the influence of W surface density and the nature of the support on the surface structure, development of the acidity, and catalytic performance of WO(x)()/ ZrO(2) catalysts. Two series of catalysts containing W surface densities up to 5.2 at. W/nm(2) were prepared by pore volume impregnation of two different supports: zirconium oxyhydroxide and predominantly tetragonal zirconia (65% tetragonal, 35% monoclinic). The texture and structure of the catalysts were investigated by BET measurements, X-ray diffraction, Raman and infrared spectroscopy. The catalytic activity was tested for 2-propanol dehydration and n-hexane isomerization. For catalysts obtained by impregnation of Zr oxyhydroxide, Raman results showed that W was present as a surface phase. Infrared spectra indicated an increase in the degree of polymerization of W species with increasing W surface density. The development of the acidity was monitored by lutidine adsorption and desorption at 523 K, followed by infrared spectroscopy. The results indicated the presence of a threshold of W surface density at 1.3 at. W/ nm(2) for the detection of these acid sites, followed by a progressive increase in their abundance with increasing W surface density. The development of Brønsted acidity correlated with the evolution of the infrared bands attributed to "extensively" polymerized W species. A direct relationship was observed between the abundance of Brønsted acid sites and the catalytic activity for 2-propanol dehydration. For n-hexane isomerization, compared to 2-propanol dehydration, a higher threshold of W surface densities (3.4 at. W/ nm(2)) for the development of activity was observed. The difference was

  19. Crystal structure of the catalytic domain of Clostridium perfringens neuraminidase in complex with a non-carbohydrate-based inhibitor, 2-(cyclohexylamino)ethanesulfonic acid.

    PubMed

    Lee, Youngjin; Youn, Hyung-Seop; Lee, Jung-Gyu; An, Jun Yop; Park, Kyoung Ryoung; Kang, Jung Youn; Ryu, Young Bae; Jin, Mi Sun; Park, Ki Hun; Eom, Soo Hyun

    2017-03-16

    Anti-bacterial and anti-viral neuraminidase agents inhibit neuraminidase activity catalyzing the hydrolysis of terminal N-acetylneuraminic acid (Neu5Ac) from glycoconjugates and help to prevent the host pathogenesis that lead to fatal infectious diseases including influenza, bacteremia, sepsis, and cholera. Emerging antibiotic and drug resistances to commonly used anti-neuraminidase agents such as oseltamivir (Tamiflu) and zanamivir (Relenza) have highlighted the need to develop new anti-neuraminidase drugs. We obtained a serendipitous complex crystal of the catalytic domain of Clostridium perfringens neuraminidase (CpNanICD) with 2-(cyclohexylamino)ethanesulfonic acid (CHES) as a buffer. Here, we report the crystal structure of CpNanICD in complex with CHES at 1.24 Å resolution. Amphipathic CHES binds to the catalytic site of CpNanICD similar to the substrate (Neu5Ac) binding site. The 2-aminoethanesulfonic acid moiety and cyclohexyl groups of CHES interact with the cluster of three arginine residues and with the hydrophobic pocket of the CpNanICD catalytic site. In addition, a structural comparison with other bacterial and human neuraminidases suggests that CHES could serve as a scaffold for the development of new anti-neuraminidase agents targeting CpNanI.

  20. 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.

  1. Continuous multistep synthesis of perillic acid from limonene by catalytic biofilms under segmented flow.

    PubMed

    Willrodt, Christian; Halan, Babu; Karthaus, Lisa; Rehdorf, Jessica; Julsing, Mattijs K; Buehler, Katja; Schmid, Andreas

    2017-02-01

    The efficiency of biocatalytic reactions involving industrially interesting reactants is often constrained by toxification of the applied biocatalyst. Here, we evaluated the combination of biologically and technologically inspired strategies to overcome toxicity-related issues during the multistep oxyfunctionalization of (R)-(+)-limonene to (R)-(+)-perillic acid. Pseudomonas putida GS1 catalyzing selective limonene oxidation via the p-cymene degradation pathway and recombinant Pseudomonas taiwanensis VLB120 were evaluated for continuous perillic acid production. A tubular segmented-flow biofilm reactor was used in order to relieve oxygen limitations and to enable membrane mediated substrate supply as well as efficient in situ product removal. Both P. putida GS1 and P. taiwanensis VLB120 developed a catalytic biofilm in this system. The productivity of wild-type P. putida GS1 encoding the enzymes for limonene bioconversion was highly dependent on the carbon source and reached 34 g Ltube(-1)  day(-1) when glycerol was supplied. More than 10-fold lower productivities were reached irrespective of the applied carbon source when the recombinant P. taiwanensis VLB120 harboring p-cymene monooxygenase and p-cumic alcohol dehydrogenase was used as biocatalyst. The technical applicability for preparative perillic acid synthesis in the applied system was verified by purification of perillic acid from the outlet stream using an anion exchanger resin. This concept enabled the multistep production of perillic acid and which might be transferred to other reactions involving volatile reactants and toxic end-products. Biotechnol. Bioeng. 2017;114: 281-290. © 2016 Wiley Periodicals, Inc.

  2. 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.

  3. Catalytic activity of metallic nanoisland coatings. The influence of size effects on the recombination properties

    NASA Astrophysics Data System (ADS)

    Tomilina, O. A.; Berzhansky, V. N.; Tomilin, S. V.; Shaposhnikov, A. N.

    2016-08-01

    The results of investigations of the quantum-size effects influence on selective properties of heterogeneous nanocatalysts are presents. As etalon exothermic reaction was used the reaction of atomic hydrogen recombination. The nanostructured Pd and Pt films on Teflon substrate were used as a samples of heterogeneous nanocatalysts. It was shown that for nanoparticles with various sizes the catalytic activity has the periodic dependence. It has been found that for certain sizes of nanoparticles their catalytic activity is less than that of Teflon substrate.

  4. 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.

  5. New potential nonsteroidal anti-inflammatory drugs with antileukotrienic effects: influence on model proteins with catalytic activity.

    PubMed

    Netopilová, Miloslava; Drsata, Jaroslav; Beránek, Martin; Palicka, Vladimír

    2002-01-01

    Unspecific and side effects caused by interaction with proteins belong to common problems of many structures synthesized as potential medicaments. Possible in vitro interactions with proteins of a group of phenylsulfonyl benzoic acid derivatives (VUFB 19363, 19369, 19370, 19371, and 19760) as new potential anti-inflammatory compounds with anti-leukotrienic activities were studied in the present work. Three purified enzymes were used as model proteins with catalytic activities: Pig heart aspartate aminotransferase (AST, EC 2.6.1.1), alanine aminotransferase (ALT, EC 2.6.1.2), and glutamate decarboxylase (GAD, EC 4.1.1.15) from E. coli. Catalytic activities during incubation of individual compounds (6 x 10(-5) M solution to 5 x 10(-2) M suspension) at 37 degrees C with enzymes served as criteria of stability and function of the proteins. No immediate influence of any compound studied on enzyme activities was found. Aminotransferase activities were not affected even during incubation up to 20 d. In the case of GAD, the compounds VUFB 19369, 19370, 19371, and 19760 had stabilizing influence on GAD activity during incubation at enzyme concentrations of 11.25 and 5.62 mg prot/l. The lack of an immediate effect of compounds and the stability of enzymes during incubation them are favorable and support the prospective of the compounds as potential drugs.

  6. Theophylline-assisted, eco-friendly synthesis of PtAu nanospheres at reduced graphene oxide with enhanced catalytic activity towards Cr(VI) reduction.

    PubMed

    Hu, Ling-Ya; Chen, Li-Xian; Liu, Meng-Ting; Wang, Ai-Jun; Wu, Lan-Ju; Feng, Jiu-Ju

    2017-05-01

    Theophylline as a naturally alkaloid is commonly employed to treat asthma and chronic obstructive pulmonary disorder. Herein, a facile theophylline-assisted green approach was firstly developed for synthesis of PtAu nanospheres/reduced graphene oxide (PtAu NSs/rGO), without any surfactant, polymer, or seed involved. The obtained nanocomposites were applied for the catalytic reduction and removal of highly toxic chromium (VI) using formic acid as a model reductant at 50°C, showing the significantly enhanced catalytic activity and improved recyclability when compared with commercial Pt/C (50%) and home-made Au nanocrystals supported rGO (Au NCs/rGO). It demonstrates great potential applications of the catalyst in wastewater treatment and environmental protection. The eco-friendly route provides a new platform to fabricate other catalysts with enhanced catalytic activity.

  7. The catalytic subunit of Dictyostelium cAMP-dependent protein kinase -- role of the N-terminal domain and of the C-terminal residues in catalytic activity and stability.

    PubMed

    Etchebehere, L C; Van Bemmelen, M X; Anjard, C; Traincard, F; Assemat, K; Reymond, C; Véron, M

    1997-09-15

    The C subunit of Dictyostelium cAMP-dependent protein kinase (PKA) is unusually large (73 kDa) due to the presence of 330 amino acids N-terminal to the conserved catalytic core. The sequence following the core, including a C-terminal -Phe-Xaa-Xaa-Phe-COOH motif, is highly conserved. We have characterized the catalytic activity and stability of C subunits mutated in sequences outside the catalytic core and we have analyzed their ability to interact with the R subunit and with the heat-stable protein-kinase inhibitor PKI. Mutants carrying deletions in the N-terminal domain displayed little difference in their kinetic properties and retained their capacity to be inhibited by R subunit and by PKI. In contrast, the mutation of one or both of the phenylalanine residues in the C-terminal motif resulted in a decrease of catalytic activity and stability of the proteins. Inhibition by the R subunit or by PKI were however unaffected. Sequence-comparison analysis of other protein kinases revealed that a -Phe-Xaa-Xaa-Phe- motif is present in many Ser/Thr protein kinases, although its location at the very end of the polypeptide is a particular feature of the PKA family. We propose that the presence of this motif may serve to identify isoforms of protein kinases.

  8. 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.

  9. CuO impregnated activated carbon for catalytic wet peroxide oxidation of phenol.

    PubMed

    Liou, Rey-May; Chen, Shih-Hsiung

    2009-12-15

    This paper presents an original approach to the removal of phenol in synthetic wastewater by catalytic wet peroxide oxidation with copper binding activated carbon (CuAC) catalysts. The characteristics and oxidation performance of CuAC in the wet hydrogen peroxide catalytic oxidation of phenol were studied in a batch reactor at 80 degrees C. Complete conversion of the oxidant, hydrogen peroxide, was observed with CuAC catalyst in 20 min oxidation, and a highly efficient phenol removal and chemical oxygen demand (COD) abatement were achieved in the first 30 min. The good oxidation performance of CuAC catalyst was contributed to the activity enhancement of copper oxide, which was binding in the carbon matrix. It can be concluded that the efficiency of oxidation dominated by the residual H2O2 in this study. An over 90% COD removal was achieved by using the multiple-step addition in this catalytic oxidation.

  10. Mutational analysis of RAG1 and RAG2 identifies three catalytic amino acids in RAG1 critical for both cleavage steps of V(D)J recombination

    PubMed Central

    Landree, Mark A.; Wibbenmeyer, Jamie A.; Roth, David B.

    1999-01-01

    RAG1 and RAG2 initiate V(D)J recombination, the process of rearranging the antigen-binding domain of immunoglobulins and T-cell receptors, by introducing site-specific double-strand breaks (DSB) in chromosomal DNA during lymphocyte development. These breaks are generated in two steps, nicking of one strand (hydrolysis), followed by hairpin formation (transesterification). The nature and location of the RAG active site(s) have remained unknown. Because acidic amino acids have a critical role in catalyzing DNA cleavage by nucleases and recombinases that require divalent metal ions as cofactors, we hypothesized that acidic active site residues are likewise essential for RAG-mediated DNA cleavage. We altered each conserved acidic amino acid in RAG1 and RAG2 by site-directed mutagenesis, and examined >100 mutants using a combination of in vivo and in vitro analyses. No conserved acidic amino acids in RAG2 were critical for catalysis; three RAG1 mutants retained normal DNA binding, but were catalytically inactive for both nicking and hairpin formation. These data argue that one active site in RAG1 performs both steps of the cleavage reaction. Amino acid substitution experiments that changed the metal ion specificity suggest that at least one of these three residues contacts the metal ion(s) directly. These data suggest that RAG-mediated DNA cleavage involves coordination of divalent metal ion(s) by RAG1. PMID:10601032

  11. New insights into the catalytic mechanism of histidine phosphatases revealed by a functionally essential arginine residue within the active site of the Sts phosphatases.

    PubMed

    San Luis, Boris; Nassar, Nicolas; Carpino, Nick

    2013-07-01

    Sts (suppressor of T-cell receptor signalling)-1 and Sts-2 are HPs (histidine phosphatases) that negatively regulate TCR (T-cell receptor) signalling pathways, including those involved in cytokine production. HPs play key roles in such varied biological processes as metabolism, development and intracellular signalling. They differ considerably in their primary sequence and substrate specificity, but possess a catalytic core formed by an invariant quartet of active-site residues. Two histidine and two arginine residues cluster together within the HP active site and are thought to participate in a two-step dephosphorylation reaction. To date there has been little insight into any additional residues that might play an important functional role. In the present study, we identify and characterize an additional residue within the Sts phosphatases (Sts-1 Arg383 or Sts-2 Arg369) that is critical for catalytic activity and intracellular function. Mutation of Sts-1 Arg383 to an alanine residue compromises the enzyme's activity and renders Sts-1 unable to suppress TCR-induced cytokine induction. Of the multiple amino acids substituted for Arg383, only lysine partially rescues the catalytic activity of Sts-1. Although Sts-1 Arg383 is conserved in all Sts homologues, it is only conserved in one of the two sub-branches of HPs. The results of the present study highlight an essential role for Sts-1 phosphatase activity in regulating T-cell activation and add a new dimension of complexity to our understanding of HP catalytic activity.

  12. 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.

  13. 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.

  14. 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

  15. 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.

  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. Phospho-N-Acetyl-Muramyl-Pentapeptide Translocase from Escherichia coli: Catalytic Role of Conserved Aspartic Acid Residues

    PubMed Central

    Lloyd, Adrian J.; Brandish, Philip E.; Gilbey, Andrea M.; Bugg, Timothy D. H.

    2004-01-01

    Phospho-N-acetyl-muramyl-pentapeptide translocase (translocase 1) catalyzes the first of a sequence of lipid-linked steps that ultimately assemble the peptidoglycan layer of the bacterial cell wall. This essential enzyme is the target of several natural product antibiotics and has recently been the focus of antimicrobial drug discovery programs. The catalytic mechanism of translocase 1 is believed to proceed via a covalent intermediate formed between phospho-N-acetyl-muramyl-pentapeptide and a nucleophilic amino acid residue. Amino acid sequence alignments of the translocase 1 family and members of the related transmembrane phosphosugar transferase superfamily revealed only three conserved residues that possess nucleophilic side chains: the aspartic acid residues D115, D116, and D267. Here we report the expression and partial purification of Escherichia coli translocase 1 as a C-terminal hexahistidine (C-His6) fusion protein. Three enzymes with the site-directed mutations D115N, D116N, and D267N were constructed, expressed, and purified as C-His6 fusions. Enzymatic analysis established that all three mutations eliminated translocase 1 activity, and this finding verified the essential role of these residues. By analogy with the structural environment of the double aspartate motif found in prenyl transferases, we propose a model whereby D115 and D116 chelate a magnesium ion that coordinates with the pyrophosphate bridge of the UDP-N-acetyl-muramyl-pentapeptide substrate and in which D267 therefore fulfills the role of the translocase 1 active-site nucleophile. PMID:14996806

  18. 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

  19. 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...

  20. Temperature-responsive enzyme-polymer nanoconjugates with enhanced catalytic activities in organic media.

    PubMed

    Zhu, Jingying; Zhang, Yifei; Lu, Diannan; Zare, Richard N; Ge, Jun; Liu, Zheng

    2013-07-11

    A general approach for preparing enzyme-polymer nanoconjugates that respond to temperature in organic media is presented. These nanoconjugates readily dissolve in organic solvents for homogenous catalysis at 40 °C and showed greatly enhanced apparent catalytic activities. The recovery of the soluble enzyme-polymer nanoconjugates is accomplished by temperature-induced precipitation.

  1. Enantioselective Synthesis of a PKC Inhibitor via Catalytic C-HBond Activation

    SciTech Connect

    Wilson, Rebecca M.; Thalji, Reema K.; Bergman, Robert G.; Ellman,Jonathan A.

    2006-02-26

    The syntheses of two biologically active molecules possessing dihydropyrroloindole cores (1 and 2) were completed using rhodium-catalyzed imine-directed C-H bond functionalization, with the second of these molecules containing a stereocenter that can be set with 90% ee during cyclization using chiral nonracemic phosphoramidite ligands. Catalytic decarbonylation and direct indole/maleimide coupling provide efficient access to 2.

  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. 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

  4. 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.

  5. Preparation, characterization, and catalytic activity of zirconocene bridged on surface of silica gel

    NASA Astrophysics Data System (ADS)

    El Majdoub, Lotfia; Shi, Yasai; Yuan, Yuan; Zhou, Annan; Abutartour, Abubaker; Xu, Qinghong

    2015-10-01

    Zirconocene catalyst supported on silica gel was prepared for olefin polymerization by surface modification of calcined silica with SiCl4, and the reaction between the modified silica and cyclopentadienyl sodium and ZrCl4. The catalyst was characterized by using Fourier-transform infrared (FT-IR) spectrometer, thermogravimetric (TG), and differential scanning calorimetric (DSC) analytic spectrometer. It was found that the metallocene structure could be formed and connected on silica surface by chemical bond. Initial catalytic tests showed that the supported metallocene was catalytically active (methylaluminoxane as a cocatalyst), producing polymer with higher molecular weight than the metallocene just immobilized on the surface of silica gel.

  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. Activity prediction of substrates in NADH-dependent carbonyl reductase by docking requires catalytic constraints and charge parameterization of catalytic zinc environment

    NASA Astrophysics Data System (ADS)

    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.

  8. Catalytic efficiency of HAP phytases is determined by a key residue in close proximity to the active site.

    PubMed

    Fu, Dawei; Li, Zhongyuan; Huang, Huoqing; Yuan, Tiezheng; Shi, Pengjun; Luo, Huiying; Meng, Kun; Yang, Peilong; Yao, Bin

    2011-05-01

    The maximum activity of Yersinia enterocolitica phytase (YeAPPA) occurs at pH 5.0 and 45 °C, and notably, its specific activity (3.28 ± 0.24 U mg(-1)) is 800-fold less than that of its Yersinia kristeensenii homolog (YkAPPA; 88% amino acid sequence identity). Sequence alignment and molecular modeling show that the arginine at position 79 (Arg79) in YeAPPA corresponding to Gly in YkAPPA as well as other histidine acid phosphatase (HAP) phytases is the only non-conserved residue near the catalytic site. To characterize the effects of the corresponding residue on the specific activities of HAP phytases, Escherichia coli EcAPPA, a well-characterized phytase with a known crystal structure, was selected for mutagenesis-its Gly73 was replaced with Arg, Asp, Glu, Ser, Thr, Leu, or Tyr. The results show that the specific activities of all of the corresponding EcAPPA mutants (17-2,400 U mg(-1)) were less than that of the wild-type phytase (3,524 U mg(-1)), and the activity levels were approximately proportional to the molecular volumes of the substituted residues' side chains. Site-directed replacement of Arg79 in YeAPPA (corresponding to Gly73 of EcAPPA) with Ser, Leu, and Gly largely increased the specific activity, which further verified the key role of the residue at position 79 for determining phytase activity. Thus, a new determinant that influences the catalytic efficiency of HAP phytases has been identified.

  9. 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.

  10. Antiprotozoal activity of betulinic acid derivatives.

    PubMed

    Domínguez-Carmona, D B; Escalante-Erosa, F; García-Sosa, K; Ruiz-Pinell, G; Gutierrez-Yapu, D; Chan-Bacab, M J; Giménez-Turba, A; Peña-Rodríguez, L M

    2010-04-01

    Betulinic acid (1), isolated from the crude extract of the leaves of Pentalinon andrieuxii (Apocynaceae), together with betulinic acid acetate (2), betulonic acid (3), betulinic acid methyl ester (4), and betulin (5) were evaluated for their antiprotozoal activity. The results showed that modifying the C-3 position increases leishmanicidal activity while modification of the C-3 and C-28 positions decreases trypanocidal activity.

  11. Highly versatile catalytic hydrogenation of carboxylic and carbonic acid derivatives using a Ru-triphos complex: molecular control over selectivity and substrate scope.

    PubMed

    vom Stein, Thorsten; Meuresch, Markus; Limper, Dominik; Schmitz, Marc; Hölscher, Markus; Coetzee, Jacorien; Cole-Hamilton, David J; Klankermayer, Jürgen; Leitner, Walter

    2014-09-24

    The complex [Ru(Triphos)(TMM)] (Triphos = 1,1,1-tris(diphenylphosphinomethyl)ethane, TMM = trimethylene methane) provides an efficient catalytic system for the hydrogenation of a broad range of challenging functionalities encompassing carboxylic esters, amides, carboxylic acids, carbonates, and urea derivatives. The key control factor for this unique substrate scope results from selective activation to generate either the neutral species [Ru(Triphos)(Solvent)H2] or the cationic intermediate [Ru(Triphos)(Solvent)(H)(H2)](+) in the presence of an acid additive. Multinuclear NMR spectroscopic studies demonstrated together with DFT investigations that the neutral species generally provides lower energy pathways for the multistep reduction cascades comprising hydrogen transfer to C═O groups and C-O bond cleavage. Carboxylic esters, lactones, anhydrides, secondary amides, and carboxylic acids were hydrogenated in good to excellent yields under these conditions. The formation of the catalytically inactive complexes [Ru(Triphos)(CO)H2] and [Ru(Triphos)(μ-H)]2 was identified as major deactivation pathways. The former complex results from substrate-dependent decarbonylation and constitutes a major limitation for the substrate scope under the neutral conditions. The deactivation via the carbonyl complex can be suppressed by addition of catalytic amounts of acids comprising non-coordinating anions such as HNTf2 (bis(trifluoromethane)sulfonimide). Although the corresponding cationic cycle shows higher overall barriers of activation, it provides a powerful hydrogenation pathway at elevated temperatures, enabling the selective reduction of primary amides, carbonates, and ureas in high yields. Thus, the complex [Ru(Triphos)(TMM)] provides a unique platform for the rational selection of reaction conditions for the selective hydrogenation of challenging functional groups and opens novel synthetic pathways for the utilization of renewable carbon sources.

  12. Mycobacteriophage Endolysins: Diverse and Modular Enzymes with Multiple Catalytic Activities

    PubMed Central

    Payne, Kimberly M.; Hatfull, Graham F.

    2012-01-01

    The mycobacterial cell wall presents significant challenges to mycobacteriophages – viruses that infect mycobacterial hosts – because of its unusual structure containing a mycolic acid-rich mycobacterial outer membrane attached to an arabinogalactan layer that is in turn linked to the peptidoglycan. Although little is known about how mycobacteriophages circumvent these barriers during the process of infection, destroying it for lysis at the end of their lytic cycles requires an unusual set of functions. These include Lysin B proteins that cleave the linkage of mycolic acids to the arabinogalactan layer, chaperones required for endolysin delivery to peptidoglycan, holins that regulate lysis timing, and the endolysins (Lysin As) that hydrolyze peptidoglycan. Because mycobacterial peptidoglycan contains atypical features including 3→3 interpeptide linkages, it is not surprising that the mycobacteriophage endolysins also have non-canonical features. We present here a bioinformatic dissection of these lysins and show that they are highly diverse and extensively modular, with an impressive number of domain organizations. Most contain three domains with a novel N-terminal predicted peptidase, a centrally located amidase, muramidase, or transglycosylase, and a C-terminal putative cell wall binding domain. PMID:22470512

  13. Temperature and the catalytic activity of enzymes: a fresh understanding.

    PubMed

    Daniel, Roy M; Danson, Michael J

    2013-09-02

    The discovery of an additional step in the progression of an enzyme from the active to inactive state under the influence of temperature has led to a better match with experimental data for all enzymes that follow Michaelis-Menten kinetics, and to an increased understanding of the process. The new model of the process, the Equilibrium Model, describes an additional mechanism by which temperature affects the activity of enzymes, with implications for ecological, metabolic, structural, and applied studies of enzymes.

  14. Impact of active phase chemical composition and dispersity on catalytic behavior in PROX reaction

    NASA Astrophysics Data System (ADS)

    Cherkezova-Zheleva, Z.; Paneva, D.; Todorova, S.; Kolev, H.; Shopska, M.; Yordanova, I.; Mitov, I.

    2014-04-01

    Iron and iron-platinum catalysts supported on activated carbon have been successfully synthesized by wet impregnation method and low-temperature treatment in inert atmosphere. The content of the supported phases corresponds to 10 wt % Fe and 0.5 wt % Pt. Four catalytic samples were synthesized: Sample A—activated carbon impregnated with Fe nitrate; Sample B—activated carbon impregnated with Pt salt; Sample C—activated carbon impregnated consequently with Fe and Pt salts; Sample D—activated carbon impregnated simultaneously with Fe and Pt salts. The as-prepared materials were characterized by Mössbauer spectroscopy, X-ray diffraction, infrared and X-ray photoelectron spectroscopy. The spectra show that the activated carbon support and the preparation procedure give rise to the synthesis of isolated metal Pt ions and ultradispersed Fe and Pt oxide species. Probably the presence of different functional groups of activated carbon gives rise to registered very high dispersion of loaded species on support. The catalytic tests were carried out in PROX reaction. A lower activity of bimetallic Pt-Fe samples was explained with the increase in surface oxygen species as a result of predomination of iron oxide on the support leading to the increase in selectivity to the H2 oxidation. Partial agglomeration of supported iron oxide phase was registered after catalytic tests.

  15. One-step preparation of magnetic recyclable quinary graphene hydrogels with high catalytic activity.

    PubMed

    Zhang, Junshuai; Yao, Tongjie; Guan, Chenchen; Zhang, Nanxi; Huang, Xin; Cui, Tieyu; Wu, Jie; Zhang, Xiao

    2017-04-01

    Metal nanoparticles (NPs) displayed overwhelming superiority in catalysis towards the corresponding bulk-phase materials; nevertheless, how to further improve catalytic activity was still an ongoing subject. Herein, we have combined one-step redox reaction and following freeze-dried technology to construct the quinary reduced graphene oxide nanosheets (rGS)/Fe2O3-PdPt/polypyrrole (PPy) hydrogels. Compared with traditional catalysts, their catalytic property was improved via two ways: construction of three-dimensional (3D) rGS hydrogels instead of two-dimensional rGS and synthesis of bimetallic alloys instead of monometallic NPs. The highly dispersed PdPt with diameter as small as 3.2nm uniformly loaded on hydrogel surface. Due to special interconnected and porous structure, the reactants were easily adsorbed in hydrogels and contacted with PdPt alloys. To explain the contributions of bimetallic alloys and 3D rGS structure on enhanced catalytic activity, the catalytic property of quinary hydrogels was compared with reference samples. Besides superior activity, they also displayed good reusability, since hydrogels could be magnetically recycled owing to the existence of Fe2O3 NPs.

  16. Analyzing the catalytic role of active site residues in the Fe-type nitrile hydratase from Comamonas testosteroni Ni1.

    PubMed

    Martinez, Salette; Wu, Rui; Krzywda, Karoline; Opalka, Veronika; Chan, Hei; Liu, Dali; Holz, Richard C

    2015-07-01

    A strictly conserved active site arginine residue (αR157) and two histidine residues (αH80 and αH81) located near the active site of the Fe-type nitrile hydratase from Comamonas testosteroni Ni1 (CtNHase), were mutated. These mutant enzymes were examined for their ability to bind iron and hydrate acrylonitrile. For the αR157A mutant, the residual activity (k cat = 10 ± 2 s(-1)) accounts for less than 1% of the wild-type activity (k cat = 1100 ± 30 s(-1)) while the K m value is nearly unchanged at 205 ± 10 mM. On the other hand, mutation of the active site pocket αH80 and αH81 residues to alanine resulted in enzymes with k cat values of 220 ± 40 and 77 ± 13 s(-1), respectively, and K m values of 187 ± 11 and 179 ± 18 mM. The double mutant (αH80A/αH81A) was also prepared and provided an enzyme with a k cat value of 132 ± 3 s(-1) and a K m value of 213 ± 61 mM. These data indicate that all three residues are catalytically important, but not essential. X-ray crystal structures of the αH80A/αH81A, αH80W/αH81W, and αR157A mutant CtNHase enzymes were solved to 2.0, 2.8, and 2.5 Å resolutions, respectively. In each mutant enzyme, hydrogen-bonding interactions crucial for the catalytic function of the αCys(104)-SOH ligand are disrupted. Disruption of these hydrogen bonding interactions likely alters the nucleophilicity of the sulfenic acid oxygen and the Lewis acidity of the active site Fe(III) ion.

  17. 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.

  18. Enhancing the catalytic activity of hydronium ions through constrained environments

    NASA Astrophysics Data System (ADS)

    Liu, Yuanshuai; Vjunov, Aleksei; Shi, Hui; Eckstein, Sebastian; Camaioni, Donald M.; Mei, Donghai; Baráth, Eszter; Lercher, Johannes A.

    2017-03-01

    The dehydration of alcohols is involved in many organic conversions but has to overcome high free-energy barriers in water. Here we demonstrate that hydronium ions confined in the nanopores of zeolite HBEA catalyse aqueous phase dehydration of cyclohexanol at a rate significantly higher than hydronium ions in water. This rate enhancement is not related to a shift in mechanism; for both cases, the dehydration of cyclohexanol occurs via an E1 mechanism with the cleavage of Cβ-H bond being rate determining. The higher activity of hydronium ions in zeolites is caused by the enhanced association between the hydronium ion and the alcohol, as well as a higher intrinsic rate constant in the constrained environments compared with water. The higher rate constant is caused by a greater entropy of activation rather than a lower enthalpy of activation. These insights should allow us to understand and predict similar processes in confined spaces.

  19. Enhancing the catalytic activity of hydronium ions through constrained environments

    PubMed Central

    Liu, Yuanshuai; Vjunov, Aleksei; Shi, Hui; Eckstein, Sebastian; Camaioni, Donald M.; Mei, Donghai; Baráth, Eszter; Lercher, Johannes A.

    2017-01-01

    The dehydration of alcohols is involved in many organic conversions but has to overcome high free-energy barriers in water. Here we demonstrate that hydronium ions confined in the nanopores of zeolite HBEA catalyse aqueous phase dehydration of cyclohexanol at a rate significantly higher than hydronium ions in water. This rate enhancement is not related to a shift in mechanism; for both cases, the dehydration of cyclohexanol occurs via an E1 mechanism with the cleavage of Cβ–H bond being rate determining. The higher activity of hydronium ions in zeolites is caused by the enhanced association between the hydronium ion and the alcohol, as well as a higher intrinsic rate constant in the constrained environments compared with water. The higher rate constant is caused by a greater entropy of activation rather than a lower enthalpy of activation. These insights should allow us to understand and predict similar processes in confined spaces. PMID:28252021

  20. 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.

  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. A strong support-effect on the catalytic activity of gold nanoparticles for hydrogen peroxide decomposition.

    PubMed

    Naya, Shin-ichi; Teranishi, Miwako; Kimura, Keisuke; Tada, Hiroaki

    2011-03-21

    Catalytic activity of gold nanoparticle (NP)-loaded metal oxide semiconductors (Au/MOs) for H(2)O(2) decomposition and chemoselective oxidation of cinnamyl alcohol to cinnamaldehyde strongly depends on both the kind of the MO-supports and the Au particle size, and Au/SrTiO(3) exhibits an extraordinary high level of activity for the H(2)O(2) decomposition exceeding that of Pt/TiO(2).

  3. 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.

  4. 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.

  5. 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.

  6. An ultra-low Pd loading nanocatalyst with efficient catalytic activity

    NASA Astrophysics Data System (ADS)

    Jin, Yunxia; Xi, Jiangbo; Zhang, Zheye; Xiao, Junwu; Xiao, Fei; Qian, Lihua; Wang, Shuai

    2015-03-01

    An ultra-low Pd loading nanocatalyst is synthesized by a convenient solution route of photochemical reduction and aqueous chemical growth. The modification of nanocatalyst structures is investigated through changing morphologies of Pd nanoclusters on the surface of ZnO nanorods. A significant enhancement in photocatalytic properties has been achieved by decorating a trace amount of Pd clusters (0.05 at%) on the surface of ZnO nanorods. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is applied to demonstrate multiple catalytic activities in the Pd-ZnO hybrid nanocatalyst, which also provides a better understanding of the relationship between the unique nanoconfigured structure and catalytic performance.An ultra-low Pd loading nanocatalyst is synthesized by a convenient solution route of photochemical reduction and aqueous chemical growth. The modification of nanocatalyst structures is investigated through changing morphologies of Pd nanoclusters on the surface of ZnO nanorods. A significant enhancement in photocatalytic properties has been achieved by decorating a trace amount of Pd clusters (0.05 at%) on the surface of ZnO nanorods. The reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) is applied to demonstrate multiple catalytic activities in the Pd-ZnO hybrid nanocatalyst, which also provides a better understanding of the relationship between the unique nanoconfigured structure and catalytic performance. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr00599j

  7. 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.

  8. Relative catalytic efficiency of ldhL- and ldhD-encoded products is crucial for optical purity of lactic acid produced by lactobacillus strains.

    PubMed

    Zheng, Zhaojuan; Sheng, Binbin; Ma, Cuiqing; Zhang, Haiwei; Gao, Chao; Su, Fei; Xu, Ping

    2012-05-01

    NAD-dependent l- and d-lactate dehydrogenases coexist in Lactobacillus genomes and may convert pyruvic acid into l-lactic acid and d-lactic acid, respectively. Our findings suggest that the relative catalytic efficiencies of ldhL- and ldhD-encoded products are crucial for the optical purity of lactic acid produced by Lactobacillus strains.

  9. Catalytic Kinetic Resolution of Saturated N-Heterocycles by Enantioselective Amidation with Chiral Hydroxamic Acids.

    PubMed

    Kreituss, Imants; Bode, Jeffrey W

    2016-12-20

    The preparation of enantioenriched chiral compounds by kinetic resolution dates back to the laboratories of Louis Pasteur in the middle of the 19th century. Unlike asymmetric synthesis, this process can always deliver enantiopure material (ee > 99%) if the reactions are allowed to proceed to sufficient conversion and the selectivity of the process is not unity (s > 1). One of the most appealing and practical variants is acylative kinetic resolution, which affords easily separable reaction products, and several highly efficient enzymatic and small molecule catalysts are available. Unfortunately, this method is applicable to limited substrate classes such as alcohols and primary benzylamines. This Account focuses on our work in catalytic acylative kinetic resolution of saturated N-heterocycles, a class of molecules that has been notoriously difficult to access via asymmetric synthesis. We document the development of hydroxamic acids as suitable catalysts for enantioselective acylation of amines through relay catalysis. Alongside catalyst optimization and reaction development, we present mechanistic studies and theoretical calculation accounting for the origins of selectivity and revealing the concerted nature of many amide-bond forming reactions. Immobilization of the hydroxamic acid to form a polymer supported reagent allows simplification of the experimental setup, improvement in product purification, and extension of the substrate scope. The kinetic resolutions are operationally straight forward: reactions proceed at room temperature and open to air conditions, without generation of difficult-to-remove side products. This was utilized to achieve decagram scale resolution of antimalarial drug mefloquine to prepare more than 50 g of (+)-erythro-meflqouine (er > 99:1) from the racemate. The immobilized quasienantiomeric acyl hydroxamic acid reagents were also exploited for a rare practical implementation of parallel kinetic resolution that affords both enantiomers of

  10. 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.

  11. Stability and phase transfer of catalytically active platinum nanoparticle suspensions

    NASA Astrophysics Data System (ADS)

    Sriram, Indira; Curtin, Alexandra E.; Chiaramonti, Ann N.; Cuchiaro, J. Hunter; Weidner, Andrew R.; Tingley, Tegan M.; Greenlee, Lauren F.; Jeerage, Kavita M.

    2015-05-01

    In this work, we present a robust synthesis protocol for platinum nanoparticles that yields a monomodal dispersion of particles that are approximately 100 nm in diameter. We determine that these particles are actually agglomerates of much smaller particles, creating a "raspberry" morphology. We demonstrate that these agglomerates are stable at room temperature for at least 8 weeks by dynamic light scattering. Furthermore, we demonstrate consistent electrocatalytic activity for methanol oxidation. Finally, we quantitatively explore the relationship between dispersion solvent and particle agglomeration; specifically, particles are found to agglomerate abruptly as solvent polarity decreases.

  12. Mechanism of activation of elongation factor Tu by ribosome: catalytic histidine activates GTP by protonation.

    PubMed

    Aleksandrov, Alexey; Field, Martin

    2013-09-01

    Elongation factor Tu (EF-Tu) is central to prokaryotic protein synthesis as it has the role of delivering amino-acylated tRNAs to the ribosome. Release of EF-Tu, after correct binding of the EF-Tu:aa-tRNA complex to the ribosome, is initiated by GTP hydrolysis. This reaction, whose mechanism is uncertain, is catalyzed by EF-Tu, but requires activation by the ribosome. There have been a number of mechanistic proposals, including those spurred by a recent X-ray crystallographic analysis of a ribosome:EF-Tu:aa-tRNA:GTP-analog complex. In this work, we have investigated these and alternative hypotheses, using high-level quantum chemical/molecular mechanical simulations for the wild-type protein and its His85Gln mutant. For both proteins, we find previously unsuggested mechanisms as being preferred, in which residue 85, either His or Gln, directly assists in the reaction. Analysis shows that the RNA has a minor catalytic effect in the wild-type reaction, but plays a significant role in the mutant by greatly stabilizing the reaction's transition state. Given the similarity between EF-Tu and other members of the translational G-protein family, it is likely that these mechanisms of ribosome-activated GTP hydrolysis are pertinent to all of these proteins.

  13. Studies on Anion Promoted Titania.1: Preparation, Characterization, and Catalytic Activity toward Alcohol and Cumene Conversion Reactions of Phosphated Titania.

    PubMed

    Parida; Acharya; Samantaray; Mishra

    1999-09-15

    Phosphate impregnated titania samples with varying amount of phosphate have been prepared by solid-solid kneading as well as aqueous impregnation method. All the samples are characterized by XRD, TG-DTA, and N(2) adsorption-desorption isotherm. Surface area is found to increase with the increase in phosphate content up to 7.5 wt% loading and thereafter decreases. The average pore diameter and crystallite size of titania decreases with the addition of phosphate. However, total acidity (determined by base adsorption method) and the catalytic activity increases with the increase in phosphate content up to 10 wt%. Phosphated samples prepared using phosphoric acid as the source of phosphate exhibit higher acidity compared to the samples prepared using (NH(4))(3)PO(4). However, the sample prepared from (NH(4))(3)PO(4) shows the presence of both acid and basic sites. Though from the cumene conversion study it is understood that phosphated samples contain both Lewis and Brønsted acid sites, the latter predominates over the former. Copyright 1999 Academic Press.

  14. E. coli histidine triad nucleotide binding protein 1 (ecHinT) is a catalytic regulator of D-alanine dehydrogenase (DadA) activity in vivo.

    PubMed

    Bardaweel, Sanaa; Ghosh, Brahma; Chou, Tsui-Fen; Sadowsky, Michael J; Wagner, Carston R

    2011-01-01

    Histidine triad nucleotide binding proteins (Hints) are highly conserved members of the histidine triad (HIT) protein superfamily. Hints comprise the most ancient branch of this superfamily and can be found in Archaea, Bacteria, and Eukaryota. Prokaryotic genomes, including a wide diversity of both gram-negative and gram-positive bacteria, typically have one Hint gene encoded by hinT (ycfF in E. coli). Despite their ubiquity, the foundational reason for the wide-spread conservation of Hints across all kingdoms of life remains a mystery. In this study, we used a combination of phenotypic screening and complementation analyses with wild-type and hinT knock-out Escherichia coli strains to show that catalytically active ecHinT is required in E. coli for growth on D-alanine as a sole carbon source. We demonstrate that the expression of catalytically active ecHinT is essential for the activity of the enzyme D-alanine dehydrogenase (DadA) (equivalent to D-amino acid oxidase in eukaryotes), a necessary component of the D-alanine catabolic pathway. Site-directed mutagenesis studies revealed that catalytically active C-terminal mutants of ecHinT are unable to activate DadA activity. In addition, we have designed and synthesized the first cell-permeable inhibitor of ecHinT and demonstrated that the wild-type E. coli treated with the inhibitor exhibited the same phenotype observed for the hinT knock-out strain. These results reveal that the catalytic activity and structure of ecHinT is essential for DadA function and therefore alanine metabolism in E. coli. Moreover, they provide the first biochemical evidence linking the catalytic activity of this ubiquitous protein to the biological function of Hints in Escherichia coli.

  15. Structure-acidity correlation of supported tungsten(VI)-oxo-species: FT-IR and TPD studies of adsorbed pyridine and catalytic decomposition of 2-propanol

    NASA Astrophysics Data System (ADS)

    Zaki, M. I.; Mekhemer, G. A. H.; Fouad, N. E.; Rabee, A. I. M.

    2014-07-01

    The amount of 10 wt%-WO3 was supported on alumina, titania or silica by impregnation with aqueous solution of ammonium paratungstate and subsequent calcination at 500 °C for 10 h. Tungstate-related chemical and physical changes in the calcination products were resolved by ex-situ infrared (IR) spectroscopy. Nature of exposed surface acid sites were probed by in-situ IR spectroscopy of adsorbed pyridine (Py) molecules at room temperature (RT). The relative strength of the acid sites thus probed was gauged by combining results of temperature-programmed desorption (TPD) measurements of the RT-adsorbed Py with those communicated by in-situ IR spectra of residual Py on the surface after a brief thermoevacuation at high temperatures (100-300 °C). Reactivity of the surface acid sites was tested toward 2-propanal catalytic decomposition, and observed by in-situ IR gas phase spectra. Results obtained were correlated with predominant structures assumed by the supported tungstate species. Accordingly, polymerization of the supported tungstate into 2-/3-dimensional structures, was found to be relatively most advanced on favorable locations of titania surfaces as compared to the case on alumina or silica surfaces. Consequently, the Lewis acidity was strengthened, and strong Bronsted acidity was evolved, leading to a 2-propanol dehydration catalyst (tungstate/titania) of optimal activity and selectivity. Strong tungstate/support interfacial interactions were found to hamper the formation of the strongly acidic and catalytically active polymeric structures of the supported tungstate (i.e., the case on alumina or silica).

  16. Quantitative and Temporal Requirements Revealed for Zap-70 Catalytic Activity During T Cell Development

    PubMed Central

    Au-Yeung, Byron B.; Melichar, Heather J.; Ross, Jenny O.; Cheng, Debra A.; Zikherman, Julie; Shokat, Kevan M.; Robey, Ellen A.; Weiss, Arthur

    2014-01-01

    The catalytic activity of Zap-70 is crucial for T cell receptor (TCR) signaling, but the quantitative and temporal requirements for its function in thymocyte development are not known. Using a chemical-genetic system to selectively and reversibly inhibit Zap-70 catalytic activity in a model of synchronized thymic selection, we showed that CD4+CD8+ thymocytes integrate multiple, transient, Zap-70-dependent signals over more than 36 h to reach a cumulative threshold for positive selection, whereas one hour of signaling was sufficient for negative selection. Titration of Zap-70 activity resulted in graded reductions in positive and negative selection but did not decrease the cumulative TCR signals integrated by positively selected OT-I cells, revealing heterogeneity, even among CD4+CD8+ thymocytes expressing identical TCRs undergoing positive selection. PMID:24908390

  17. Catalytic hydrogenation of amino acids to amino alcohols with complete retention of configuration.

    PubMed

    Tamura, Masazumi; Tamura, Riku; Takeda, Yasuyuki; Nakagawa, Yoshinao; Tomishige, Keiichi

    2014-06-25

    Rh-MoOx/SiO2 is an effective heterogeneous catalyst for selective hydrogenation of amino acids to amino alcohols in a water solvent. MoOx modification of Rh drastically enhanced the activity and improved the selectivity and ee. Various amino alcohols were obtained in high yields (90-94%) with complete retention of configuration.

  18. Human platelet heparanase: purification, characterization and catalytic activity.

    PubMed Central

    Freeman, C; Parish, C R

    1998-01-01

    Heparan sulphate (HS) is an important component of the extracellular matrix (ECM) and the vasculature basal lamina (BL) which functions as a barrier to the extravasation of metastatic and inflammatory cells. Platelet-tumour cell aggregation at the capillary endothelium results in activation and degranulation of platelets. Cleavage of HS by endoglycosidase or heparanase activity produced in relatively large amounts by the platelets and the invading cells may assist in the disassembly of the ECM and BL, and thereby facilitate cell migration. Using a recently published rapid, quantitative assay for heparanase activity towards HS [Freeman, C. and Parish, C.R. (1997), Biochem. J., 325, 229-237], human platelet heparanase has now been purified 1700-fold to homogeneity in 19% yield by a five column procedure, which consists of concanavalin A-Sepharose, Zn2+-chelating-Sepharose, Blue A-agarose, octyl-agarose and gel filtration chromatography. The enzyme, which was shown to be an endoglucuronidase that degrades both heparin and HS, has a native molecular mass of 50 kDa when analysed by gel filtration chromatography and by SDS/PAGE. Platelet heparanase degraded porcine mucosal HS in a stepwise fashion from a number average molecular mass of 18.5 to 13, to 8 and finally to 4.5 kDa fragments as determined by gel filtration analysis. Bovine lung heparin was degraded from 8.9 to 4.8 kDa while porcine mucosal heparin was degraded from 8.1 kDa to 3.8 and finally to 2.9 kDa fragments. Studies of the enzyme's substrate specificity using modified heparin analogues showed that substrate cleavage required the presence of carboxyl groups, but O- and N-sulphation were not essential. Inhibition studies demonstrated an absolute requirement for the presence of O-sulphate groups. Platelet heparanase was inhibited by heparin analogues which also inhibited tumour heparanase, suggesting that sulphated polysaccharides which inhibit tumour metastasis may act to prevent both tumour cell and

  19. In situ synthesis, characterization, and catalytic performance of tungstophosphoric acid encapsulated into the framework of mesoporous silica pillared clay.

    PubMed

    Li, Baoshan; Liu, Zhenxing; Han, Chunying; Ma, Wei; Zhao, Songjie

    2012-07-01

    Mesoporous silica pillared clay (SPC) incorporated with tungstophosphoric acid (HPW) has been synthesized via in situ introducing P and W source in the acidic suspension of the clay interlayer template during the formation of the silica pillared clay. The samples were characterized by XRD, XRF, FT-IR, TG-DTA, N(2) adsorption-desorption, and SEM techniques. The results showed that the HPW formed by in situ method has been effectively introduced into the framework of mesoporous silica pillared clay and its Keggin structure remained perfectly after formation of the materials. In addition, samples with similar HPW loadings were also prepared by impregnation method using SPC as the support. HPW in the incorporated samples was better dispersed into the silica pillared clay than in the impregnated samples. The results of catalytic tests indicated that the encapsulated materials demonstrated better catalytic performance than the impregnated samples in oxidative desulfurization (ODS) of dibenzothiophene (DBT).

  20. Polymeric enzyme mimics: catalytic activity of ribose-containing polymers for a phosphate substrate.

    PubMed

    Han, Man Jung; Yoo, Kyung Soo; Kim, Young Heui; Chang, Ji Young

    2003-07-07

    The polymers containing ribose rings: poly(5'-acrylamido-5'-deoxy-1',2'-O-isopropylidene-alpha-D-ribose) (11), poly(5'-acrylamido-5'-deoxy-alpha-D-ribose) (12) and poly(5'-acrylamido-5'-deoxy-1'-O-methyl-D-ribose) (13) were prepared as enzyme mimics. Polymers 12 and 13 with free vic-cis-diol groups catalyzed the hydrolysis of phosphodiester (ethyl p-nitrophenyl phosphate and N-methylpyridinium 4-tert-butylcatechol cyclic phosphate) and phosphomonoester substrates with a rate acceleration of 10 approximately equal to 10(3) compared with the uncatalyzed reaction. They also catalyzed the reverse reactions, i.e., the esterification of phosphomonoester to phosphodiester and the phosphorylation of alcohols with phosphate ions. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles. The catalytic activity was negligible for polymer 11 where vic-cis-diol groups were blocked with isopropylidene groups. The catalytic activity was attributable to the vic-cis-diols of riboses on polymer chains, which formed hydrogen bonds with two phosphoryl oxygen atoms of phosphates so as to activate the phosphorus atoms to be attacked by nucleophiles.

  1. 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.

  2. Synergy of Lewis and Brønsted acids on catalytic hydrothermal decomposition of carbohydrates and corncob acid hydrolysis residues to 5-hydroxymethylfurfural

    PubMed Central

    Wang, Chao; Zhang, Liming; Zhou, Tian; Chen, Jiachuan; Xu, Feng

    2017-01-01

    5-hydroxymethylfurfural (HMF) is an important platform molecule in the synthesis of various chemicals and materials. Herein, we reported a simple and effective dehydration of glucose-based carbohydrates to HMF in a biphasic system containing cyclopentyl methyl ether as the organic phase and AlCl3 with minute amounts of HCl as co-catalysts. The results showed that the mixed catalysts had a positive synergistic catalytic effect on glucose conversion to HMF compared with single AlCl3 or HCl catalyst. For glucose, the highest HMF yield of 54.5% was achieved at 175 °C for 20 min. More importantly, the optimal catalytic system was so efficient that it achieved one of the highest reported yields of HMF (30.5%) directly from corncob acid hydrolysis residues. Thus, the catalytic system can become a promising route for effective utilization of biomass in future biorefineries. PMID:28084456

  3. 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.

  4. Comprehensive Characterization of AMP-activated Protein Kinase Catalytic Domain by Top-down Mass Spectrometry

    PubMed Central

    Yu, Deyang; Peng, Ying; Ayaz-Guner, Serife; Gregorich, Zachery R.; Ge, Ying

    2015-01-01

    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 has 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. PMID:26489410

  5. When ruthenia met titania: Achieving extraordinary catalytic activity at low temperature by nanostructuring of oxides

    DOE PAGES

    Graciani, J.; Stacchiola, D.; Yang, 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

  6. 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.

  7. The proteolytic system of pineapple stems revisited: Purification and characterization of multiple catalytically active forms.

    PubMed

    Matagne, André; Bolle, Laetitia; El Mahyaoui, Rachida; Baeyens-Volant, Danielle; Azarkan, Mohamed

    2017-02-23

    Crude pineapple proteases extract (aka stem bromelain; EC 3.4.22.4) is an important proteolytic mixture that contains enzymes belonging to the cysteine proteases of the papain family. Numerous studies have been reported aiming at the fractionation and characterization of the many molecular species present in the extract, but more efforts are still required to obtain sufficient quantities of the various purified protease forms for detailed physicochemical, enzymatic and structural characterization. In this work, we describe an efficient strategy towards the purification of at least eight enzymatic forms. Thus, following rapid fractionation on a SP-Sepharose FF column, two sub-populations with proteolytic activity were obtained: the unbound (termed acidic) and bound (termed basic) bromelain fractions. Following reversible modification with monomethoxypolyethylene glycol (mPEG), both fractions were further separated on Q-Sepharose FF and SP-Sepharose FF, respectively. This procedure yielded highly purified molecular species, all titrating ca. 1 mol of thiol group per mole of enzyme, with distinct biochemical properties. N-terminal sequencing allowed identifying at least eight forms with proteolytic activity. The basic fraction contained previously identified species, i.e. basic bromelain forms 1 and 2, ananain forms 1 and 2, and comosain (MEROPS identifier: C01.027). Furthermore, a new proteolytic species, showing similarities with basic bomelain forms 1 and 2, was discovered and termed bromelain form 3. The two remaining species were found in the acidic bromelain fraction and were arbitrarily named acidic bromelain forms 1 and 2. Both, acidic bromelain forms 1, 2 and basic bromelain forms 1, 2 and 3 are glycosylated, while ananain forms 1 and 2, and comosain are not. The eight protease forms display different amidase activities against the various substrates tested, namely small synthetic chromogenic compounds (DL-BAPNA and Boc-Ala-Ala-Gly-pNA), fluorogenic compounds

  8. 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

    2016-09-08

    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.

  9. 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.

  10. 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.

  11. Bicarbonate Modulates Photoreceptor Guanylate Cyclase (ROS-GC) Catalytic Activity*

    PubMed Central

    Duda, Teresa; Wen, Xiao-Hong; Isayama, Tomoki; Sharma, Rameshwar K.; Makino, Clint L.

    2015-01-01

    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 [Ca2+]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 Ca2+ nor use of the GCAPs domains; however, stimulation of ROS-GC1 was more powerful in the presence of GCAP1 or GCAP2 at low [Ca2+]. 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

  12. Rational design of ornithine decarboxylase with high catalytic activity for the production of putrescine.

    PubMed

    Choi, Hyang; Kyeong, Hyun-Ho; Choi, Jung Min; Kim, Hak-Sung

    2014-09-01

    Putrescine finds wide industrial applications in the synthesis of polymers, pharmaceuticals, agrochemicals, and surfactants. Owing to economic and environmental concerns, the microbial production of putrescine has attracted a great deal of attention, and ornithine decarboxylase (ODC) is known to be a key enzyme in the biosynthetic pathway. Herein, we present the design of ODC from Escherichia coli with high catalytic efficiency using a structure-based rational approach. Through a substrate docking into the model structure of the enzyme, we first selected residues that might lead to an increase in catalytic activity. Of the selected residues that are located in the α-helix and the loops constituting the substrate entry site, a mutational analysis of the single mutants identified two key residues, I163 and E165. A combination of two single mutations resulted in a 62.5-fold increase in the catalytic efficiency when compared with the wild-type enzyme. Molecular dynamics simulations of the best mutant revealed that the substrate entry site becomes more flexible through mutations, while stabilizing the formation of the dimeric interface of the enzyme. Our approach can be applied to the design of other decarboxylases with high catalytic efficiency for the production of various chemicals through bio-based processes.

  13. 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.

  14. The cooperative effect between active site ionized groups and water desolvation controls the alteration of acid/base catalysis in serine proteases.

    PubMed

    Shokhen, Michael; Khazanov, Netaly; Albeck, Amnon

    2007-08-13

    What is the driving force that alters the catalytic function of His57 in serine proteases between general base and general acid in each step along the enzymatic reaction? The stable tetrahedral complexes (TC) of chymotrypsin with trifluoromethyl ketone transition state analogue inhibitors are topologically similar to the catalytic transition state. Therefore, they can serve as a good model to study the enzyme catalytic reaction. We used DFT quantum mechanical calculations to analyze the effect of solvation and of polar factors in the active site of chymotrypsin on the pKa of the catalytic histidine in FE (the free enzyme), EI (the noncovalent enzyme inhibitor complex), and TC. We demonstrated that the acid/base alteration is controlled by the charged groups in the active site--the catalytic Asp102 carboxylate and the oxyanion. The effect of these groups on the catalytic His is modulated by water solvation of the active site.

  15. Catalytic activity and thermal stability of horseradish peroxidase encapsulated in self-assembled organic nanotubes.

    PubMed

    Lu, Qin; Kim, Youngchan; Bassim, Nabil; Raman, Nisha; Collins, Greg E

    2016-04-07

    Horseradish peroxidase (HRP) was encapsulated in self-assembled lithocholic acid (LCA) based organic nanotubes and its catalytic activity before and after thermal treatment was measured for comparison with free HRP. The apparent kcat (kcat/Km) for nanotube encapsulated HRP remained almost the same before and after thermal treatment, reporting an average value of 3.7 ± 0.4 μM(-1) s(-1). The apparent kcat value for free HRP decreased from 14.8 ± 1.3 μM(-1) s(-1) for samples stored at 4 °C to 2.4 ± 0.1 μM(-1) s(-1) after thermal treatment for 8 h at 55 °C. The Michaelis-Menten constants, Km, determined for encapsulated HRP and free HRP were relatively unperturbed by storage conditions at 4 °C or thermally treated at 55 °C for varying time periods from 2-8 h, with encapsulated HRP having a slightly higher Km than free HRP (13.4 ± 0.9 μM versus 11.7 ± 0.4 μM). The amount of HRP encapsulated in LCA nanotubes increased dramatically when the mixture of HRP and LCA nanotubes was brought to an elevated temperature. Within 4 h of thermal treatment at 55 °C, the amount of HRP encapsulated by the LCA nanotubes was more than 4 times the amount of HRP encapsulated when equilibrated at 4 °C for 7 days. Molecular dynamics (MD) simulations show that the higher degree of exposure of hydrophobic residues in HRP at elevated temperatures enhances the hydrophobic interaction between HRP and the nanotube wall, resulting in the increased amount of HRP surface adsorption and, hence, the overall amount of encapsulation inside the nanotubes.

  16. 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.

  17. 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.; ...

    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

  18. A dual arylboronic acid--aminothiourea catalytic system for the asymmetric intramolecular hetero-Michael reaction of α,β-unsaturated carboxylic acids.

    PubMed

    Azuma, Takumi; Murata, Akihiro; Kobayashi, Yusuke; Inokuma, Tsubasa; Takemoto, Yoshiji

    2014-08-15

    A bifunctional aminoboronic acid has been used to facilitate for the first time the intramolecular aza- and oxa-Michael reactions of α,β-unsaturated carboxylic acids. The combination of an arylboronic acid with a chiral aminothiourea allowed for these reactions to proceed successfully in an enantioselective manner to afford the desired heterocycles in high yields and ee's (up to 96% ee). The overall utility of this dual catalytic system was demonstrated by a one-pot enantioselective synthesis of (+)-erythrococcamide B, which proceeded via sequential Michael and amidation reactions.

  19. 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

  20. 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.; ...

    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

  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. 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

  3. An improved d-band model of the catalytic activity of magnetic transition metal surfaces

    PubMed Central

    Bhattacharjee, Satadeep; Waghmare, Umesh V.; Lee, Seung-Cheol

    2016-01-01

    The d-band center model of Hammer and Nørskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH3 molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions. PMID:27808100

  4. An improved d-band model of the catalytic activity of magnetic transition metal surfaces

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Satadeep; Waghmare, Umesh V.; Lee, Seung-Cheol

    2016-11-01

    The d-band center model of Hammer and Nørskov is widely used in understanding and predicting catalytic activity on transition metal (TM) surfaces. Here, we demonstrate that this model is inadequate for capturing the complete catalytic activity of the magnetically polarized TM surfaces and propose its generalization. We validate the generalized model through comparison of adsorption energies of the NH3 molecule on the surfaces of 3d TMs (V, Cr, Mn, Fe, Co, Ni, Cu and Zn) determined with spin-polarized density functional theory (DFT)-based methods with the predictions of our model. Compared to the conventional d-band model, where the nature of the metal-adsorbate interaction is entirely determined through the energy and the occupation of the d-band center, we emphasize that for the surfaces with high spin polarization, the metal-adsorbate system can be stabilized through a competition of the spin-dependent metal-adsorbate interactions.

  5. 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.

  6. 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.

  7. Intrinsic catalytic activity of Au nanoparticles with respect to hydrogen peroxide decomposition and superoxide scavenging.

    PubMed

    He, Weiwei; Zhou, Yu-Ting; Wamer, Wayne G; Hu, Xiaona; Wu, Xiaochun; Zheng, Zhi; Boudreau, Mary D; Yin, Jun-Jie

    2013-01-01

    Gold nanoparticles have received a great deal of interest due to their unique optical and catalytic properties and biomedical applications. Developing applications as well as assessing associated risks requires an understanding of the interactions between Au nanoparticles (NPs) and biologically active substances. In this paper, electron spin resonance spectroscopy (ESR) was used to investigate the catalytic activity of Au NPs in biologically relevant reactions. We report here that Au NPs can catalyze the rapid decomposition of hydrogen peroxide. Decomposition of hydrogen peroxide is accompanied by the formation of hydroxyl radicals at lower pH and oxygen at higher pH. In addition, we found that, mimicking SOD, Au NPs efficiently catalyze the decomposition of superoxide. These results demonstrate that Au NPs can act as SOD and catalase mimetics. Since reactive oxygen species are biologically relevant products being continuously generated in cells, these results obtained under conditions resembling different biological microenvironments may provide insights for evaluating risks associated with Au NPs.

  8. High catalytic activity of anatase titanium dioxide for decomposition of electrolyte solution in lithium ion battery

    NASA Astrophysics Data System (ADS)

    Liu, Ming; He, Yan-Bing; Lv, Wei; Zhang, Chen; Du, Hongda; Li, Baohua; Yang, Quan-Hong; Kang, Feiyu

    2014-12-01

    It has been indicated that anatase TiO2 is a promising anode material for lithium ion power battery from many previous researches. Whereas, in this work, we find that the anatase TiO2, when used as an anode for lithium ion battery, has high catalytic activity to initiate the decarboxylation reaction of electrolyte solution, resulting in the large generation of sole gaseous component, CO2. The ROLi species and the new phase of flake-like Li2TiF6 material are the main reaction products between anatase TiO2 and LiPF6 based electrolyte solution. This work provides important and urgent information that the surface chemistry of anatase TiO2 used as the anode material of lithium ion battery must be modified to suppress its catalytic activity for the decomposition of solvents.

  9. 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.

  10. 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.

  11. A Disintegrin and Metalloproteinase with Thrombospondin Motifs-5 (ADAMTS-5) Forms Catalytically Active Oligomers*

    PubMed Central

    Kosasih, Hansen J.; Last, Karena; Rogerson, Fraser M.; Golub, Suzanne B.; Gauci, Stephanie J.; Russo, Vincenzo C.; Stanton, Heather; Wilson, Richard; Lamande, Shireen R.; Holden, Paul; Fosang, Amanda J.

    2016-01-01

    The metalloproteinase ADAMTS-5 (A disintegrin and metalloproteinase with thrombospondin motifs) degrades aggrecan, a proteoglycan essential for cartilage structure and function. ADAMTS-5 is the major aggrecanase in mouse cartilage, and is also likely to be the major aggrecanase in humans. ADAMTS-5 is a multidomain enzyme, but the function of the C-terminal ancillary domains is poorly understood. We show that mutant ADAMTS-5 lacking the catalytic domain, but with a full suite of ancillary domains inhibits wild type ADAMTS activity, in vitro and in vivo, in a dominant-negative manner. The data suggest that mutant ADAMTS-5 binds to wild type ADAMTS-5; thus we tested the hypothesis that ADAMTS-5 associates to form oligomers. Co-elution, competition, and in situ PLA experiments using full-length and truncated recombinant ADAMTS-5 confirmed that ADAMTS-5 molecules interact, and showed that the catalytic and disintegrin-like domains support these intermolecular interactions. Cross-linking experiments revealed that recombinant ADAMTS-5 formed large, reduction-sensitive oligomers with a nominal molecular mass of ∼400 kDa. The oligomers were unimolecular and proteolytically active. ADAMTS-5 truncates comprising the disintegrin and/or catalytic domains were able to competitively block full-length ADAMTS-5-mediated aggrecan cleavage, measured by production of the G1-EGE373 neoepitope. These results show that ADAMTS-5 oligomerization is required for full aggrecanase activity, and they provide evidence that blocking oligomerization inhibits ADAMTS-5 activity. The data identify the surface provided by the catalytic and disintegrin-like domains of ADAMTS-5 as a legitimate target for the design of aggrecanase inhibitors. PMID:26668318

  12. New water-soluble Mn-porphyrin with catalytic activity for superoxide dismutation and peroxynitrite decomposition.

    PubMed

    Asayama, Shoichiro; Nakajima, Takumi; Kawakami, Hiroyoshi

    2011-07-01

    We have synthesized a new water-soluble cationic Mn-porphyrin with catalytic activity for both superoxide dismutation and peroxynitrite decomposition. The resulting Mn-porphyrin also showed higher stability for reactive oxygen species such as hydrogen peroxide and lower cytotoxicity, when compared with a control normal Mn-porphyrin. Furthermore, the new porphyrin recovered the viability of lipopolysaccharide-stimulated macrophage RAW 264.7 cells but the control Mn-porphyrin did not.

  13. 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.

  14. 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.

  15. Hierarchically nanoporous ceria nanoparticles with a high-surface area: synthesis, characterization, and their catalytic activity.

    PubMed

    Ge, Jiechao; Zhong, Liangshu; Zhuo, Linhai; Tang, Bo; Song, Weiguo

    2011-01-01

    A redox route based on ethylene glycol mediated process was developed to synthesize hierarchically nanoporpous ceria nanoparticles (ceria HNPNPs). The synthesized ceria HNPNPs are composed of building blocks fabricated with cubic ceria nanocrystals of several nanometers in diameter. Scanning electron microscopy was performed to investigate the evolution process of ceria precursor, and a two-step growth process was suggested for the morphology evolution. The synthesized ceria HNPNPs exhibit high surface area, which lead to high catalytic activity for CO oxidation.

  16. Preparation, characterization and application in deep catalytic ODS of the mesoporous silica pillared clay incorporated with phosphotungstic acid.

    PubMed

    Li, Baoshan; Liu, Zhenxing; Liu, Jianjun; Zhou, Zhiyuan; Gao, Xiaohui; Pang, Xinmei; Sheng, Huiting

    2011-10-15

    Mesoporous silica pillared clay (SPC) materials with different contents of H(3)PW(12)O(40) (HPW) heteropoly acid were synthesized by introducing HPW into clay interlayer template in an acidic suspension using sol-gel method. Samples with similar HPW loadings were also prepared by impregnation method using SPC as the support. The results of the characterizations showed that HPW was dispersed more homogeneously in the encapsulated samples than in the impregnated samples. The encapsulated materials exhibited better catalytic performance than the impregnated samples in oxidative desulfurization of dibenzothiophene-containing model oil. The sulfur removal reached up to 98.6% for the model oil under the experiential conditions.

  17. Essential role of PSM/SH2-B variants in insulin receptor catalytic activation and the resulting cellular responses.

    PubMed

    Zhang, Manchao; Deng, Youping; Tandon, Ruchi; Bai, Cheng; Riedel, Heimo

    2008-01-01

    The positive regulatory role of PSM/SH2-B downstream of various mitogenic receptor tyrosine kinases or gene disruption experiments in mice support a role of PSM in the regulation of insulin action. Here, four alternative PSM splice variants and individual functional domains were compared for their role in the regulation of specific metabolic insulin responses. We found that individual PSM variants in 3T3-L1 adipocytes potentiated insulin-mediated glucose and amino acid transport, glycogenesis, lipogenesis, and key components in the metabolic insulin response including p70 S6 kinase, glycogen synthase, glycogen synthase kinase 3 (GSK3), Akt, Cbl, and IRS-1. Highest activity was consistently observed for PSM alpha, followed by beta, delta, and gamma with decreasing activity. In contrast, dominant-negative peptide mimetics of the PSM Pro-rich, pleckstrin homology (PH), or src homology 2 (SH2) domains inhibited any tested insulin response. Potentiation of the insulin response originated at the insulin receptor (IR) kinase level by PSM variant-specific regulation of the Km (ATP) whereas the Vmax remained unaffected. IR catalytic activation was inhibited by peptide mimetics of the PSM SH2 or dimerization domain (DD). Either peptide should disrupt the complex of a PSM dimer linked to IR via SH2 domains as proposed for PSM activation of tyrosine kinase JAK2. Either peptide abolished downstream insulin responses indistinguishable from PSM siRNA knockdown. Our results implicate an essential role of the PSM variants in the activation of the IR kinase and the resulting metabolic insulin response. PSM variants act as internal IR ligands that in addition to potentiating the insulin response stimulate IR catalytic activation even in the absence of insulin.

  18. 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.

  19. Insight into the Mechanism of Intramolecular Inhibition of the Catalytic Activity of Sirtuin 2 (SIRT2).

    PubMed

    Li, Jinyu; Flick, Franziska; Verheugd, Patricia; Carloni, Paolo; Lüscher, Bernhard; Rossetti, Giulia

    2015-01-01

    Sirtuin 2 (SIRT2) is a NAD+-dependent deacetylase that has been associated with neurodegeneration and cancer. SIRT2 is composed of a central catalytic domain, the structure of which has been solved, and N- and C-terminal extensions that are thought to control SIRT2 function. However structural information of these N- and C-terminal regions is missing. Here, we provide the first full-length molecular models of SIRT2 in the absence and presence of NAD+. We also predict the structural alterations associated with phosphorylation of SIRT2 at S331, a modification that inhibits catalytic activity. Bioinformatics tools and molecular dynamics simulations, complemented by in vitro deacetylation assays, provide a consistent picture based on which the C-terminal region of SIRT2 is suggested to function as an autoinhibitory region. This has the capacity to partially occlude the NAD+ binding pocket or stabilize the NAD+ in a non-productive state. Furthermore, our simulations suggest that the phosphorylation at S331 causes large conformational changes in the C-terminal region that enhance the autoinhibitory activity, consistent with our previous findings that phosphorylation of S331 by cyclin-dependent kinases inhibits SIRT2 catalytic activity. The molecular insight into the role of the C-terminal region in controlling SIRT2 function described in this study may be useful for future design of selective inhibitors targeting SIRT2 for therapeutic applications.

  20. 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.

  1. 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}.

  2. Catalytic activity of human carbonic anhydrase isoform IX is displayed both extra- and intracellularly.

    PubMed

    Klier, Michael; Jamali, Somayeh; Ames, Samantha; Schneider, Hans-Peter; Becker, Holger M; Deitmer, Joachim W

    2016-01-01

    Most carbonic anhydrases catalyse the reversible conversion of carbon dioxide to protons and bicarbonate, either as soluble cytosolic enzymes, in or at intracellular organelles, or at the extracellular face of the cell membrane as membrane-anchored proteins. Carbonic anhydrase isoform IX (CA IX), a membrane-bound enzyme with catalytic activity at the extracellular membrane surface, has come to prominence in recent years because of its association with hypoxic tissue, particularly tumours, often indicating poor prognosis. We have evaluated the catalytic activity of CA IX heterologously expressed in Xenopus laevis oocytes by measuring the amplitude and rate of cytosolic pH changes as well as pH changes at the outer membrane surface (pHs ) during addition and removal of 5% CO2 /25 mm HCO3-, and by mass spectrometry. Our results indicate both extracellular and intracellular catalytic activity of CA IX. Reduced rates of CO2 -dependent intracellular pH changes after knockdown of CA IX confirmed these findings in two breast cancer cell lines: MCF-7 and MDA-MB-231. Our results demonstrate a new function of CA IX that may be important in the search for therapeutic cancer drugs targeting CA IX.

  3. Silver residues as a possible key to a remarkable oxidative catalytic activity of nanoporous gold.

    PubMed

    Moskaleva, Lyudmila V; Röhe, Sarah; Wittstock, Arne; Zielasek, Volkmar; Klüner, Thorsten; Neyman, Konstantin M; Bäumer, Marcus

    2011-03-14

    Recently, several forms of unsupported gold were shown to display a remarkable activity to catalyze oxidation reactions. Experimental evidence points to the crucial role of residual silver present in very small concentrations in these novel catalysts. We focus on the catalytic properties of nanoporous gold (np-Au) foams probed via CO and oxygen adsorption/co-adsorption. Experimental results are analyzed using theoretical models represented by the flat Au(111) and the kinked Au(321) slabs with Ag impurities. We show that Ag atoms incorporated into gold surfaces can facilitate the adsorption and dissociation of molecular oxygen on them. CO adsorbed on top of 6-fold coordinated Au atoms can in turn be stabilized by co-adsorbed atomic oxygen by up to 0.2 eV with respect to the clean unsubstituted gold surface. Our experiments suggest a linking of that most strongly bound CO adsorption state to the catalytic activity of np-Au. Thus, our results shed light on the role of silver admixtures in the striking catalytic activity of unsupported gold nanostructures.

  4. 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.

  5. Direct Single-Enzyme Biomineralization of Catalytically Active Ceria and Ceria-Zirconia Nanocrystals.

    PubMed

    Curran, Christopher D; Lu, Li; Jia, Yue; Kiely, Christopher J; Berger, Bryan W; McIntosh, Steven

    2017-02-21

    Biomineralization is an intriguing approach to the synthesis of functional inorganic materials for energy applications whereby biological systems are engineered to mineralize inorganic materials and control their structure over multiple length scales under mild reaction conditions. Herein we demonstrate a single-enzyme-mediated biomineralization route to synthesize crystalline, catalytically active, quantum-confined ceria (CeO2-x) and ceria-zirconia (Ce1-yZryO2-x) nanocrystals for application as environmental catalysts. In contrast to typical anthropogenic synthesis routes, the crystalline oxide nanoparticles are formed at room temperature from an otherwise inert aqueous solution without the addition of a precipitant or additional reactant. An engineered form of silicatein, rCeSi, as a single enzyme not only catalyzes the direct biomineralization of the nanocrystalline oxides but also serves as a templating agent to control their morphological structure. The biomineralized nanocrystals of less than 3 nm in diameter are catalytically active toward carbon monoxide oxidation following an oxidative annealing step to remove carbonaceous residue. The introduction of zirconia into the nanocrystals leads to an increase in Ce(III) concentration, associated catalytic activity, and the thermal stability of the nanocrystals.

  6. Investigating the role of chain and linker length on the catalytic activity of an H 2 production catalyst containing a β-hairpin peptide

    SciTech Connect

    Reback, Matthew L.; Ginovska, Bojana; Buchko, Garry W.; Dutta, Arnab; Priyadarshani, Nilusha; Kier, Brandon L.; Helm, Monte L.; Raugei, Simone; Shaw, Wendy J.

    2016-06-02

    Building on our recent report of an active H2 production catalyst [Ni(PPh2NProp-peptide)2]2+ (Prop=para-phenylpropionic acid, peptide (R10)=WIpPRWTGPR-NH2, p=D-proline, and P2N=1-aza-3,6-diphosphacycloheptane) that contains structured -hairpin peptides, here we investigate how H2 production is effected by: (1) the length of the hairpin (eight or ten residues) and (2) limiting the flexibility between the peptide and the core complex by altering the length of the linker: para-phenylpropionic acid (three carbons) or para-benzoic acid (one carbon). Reduction of the peptide chain length from ten to eight residues increases or maintains the catalytic current for H2 production for all complexes, suggesting a non-productive steric interaction at longer peptide lengths. While the structure of the hairpin appears largely intact for the complexes, NMR data are consistent with differences in dynamic behavior which may contribute to the observed differences in catalytic activity. Molecular dynamics simulations demonstrate that complexes with a one-carbon linker have the desired effect of restricting the motion of the hairpin relative to the complex; however, the catalytic currents are significantly reduced compared to complexes containing a three-carbon linker as a result of the electron withdrawing nature of the -COOH group. These results demonstrate the complexity and interrelated nature of the outer coordination sphere on catalysis.

  7. 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.

  8. 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...

  9. 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.

  10. Influence of physicochemical treatments on iron-based spent catalyst for catalytic oxidation of toluene.

    PubMed

    Kim, Sang Chai; Shim, Wang Geun

    2008-06-15

    The catalytic oxidation of toluene was studied over an iron-based spent and regenerated catalysts. Air, hydrogen, or four different acid solutions (oxalic acid (C2H2O4), citric acid (C6H8O7), acetic acid (CH3COOH), and nitric acid (HNO3)) were employed to regenerate the spent catalyst. The properties of pretreated spent catalyst were characterized by the Brunauer Emmett Teller (BET), inductively coupled plasma (ICP), temperature programmed reduction (TPR), and X-ray diffraction (XRD) analyses. The air pretreatment significantly enhanced the catalytic activity of the spent catalyst in the pretreatment temperature range of 200-400 degrees C, but its catalytic activity diminished at the pretreatment temperature of 600 degrees C. The catalytic activity sequence with respect to the air pretreatment temperatures was 400 degrees C>200 degrees C>parent>600 degrees C. The TPR results indicated that the catalytic activity was correlated with both the oxygen mobility and the amount of available oxygen on the catalyst. In contrast, the hydrogen pretreatment had a negative effect on the catalytic activity, and toluene conversion decreased with increasing pretreatment temperatures (200-600 degrees C). The XRD and TPR results confirmed the formation of metallic iron which had a negative effect on the catalytic activity with increasing pretreatment temperature. The acid pretreatment improved the catalytic activity of the spent catalyst. The catalytic activity sequence with respect to different acids pretreatment was found to be oxalic acid>citric acid>acetic acid>or=nitric acid>parent. The TPR results of acid pretreated samples showed an increased amount of available oxygen which gave a positive effect on the catalytic activity. Accordingly, air or acid pretreatments were more promising methods of regenerating the iron-based spent catalyst. In particular, the oxalic acid pretreatment was found to be most effective in the formation of FeC2O4 species which contributed highly to the

  11. 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

    2014-09-02

    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.

  12. 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

    2015-11-05

    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.

  13. Vesicles protect activated acetic acid.

    PubMed

    Todd, Zoe R; House, Christopher H

    2014-10-01

    Abstract Methyl thioacetate, or activated acetic acid, has been proposed to be central to the origin of life and an important energy currency molecule in early cellular evolution. We have investigated the hydrolysis of methyl thioacetate under various conditions. Its uncatalyzed rate of hydrolysis is about 3 orders of magnitude faster (K=0.00663 s(-1); 100°C, pH 7.5, concentration=0.33 mM) than published rates for its catalyzed production, making it unlikely to accumulate under prebiotic conditions. However, our experiments showed that methyl thioacetate was protected from hydrolysis when inside its own hydrophobic droplets. Further, we found that methyl thioacetate protection from hydrolysis was also possible in droplets of hexane and in the membranes of nonanoic acid vesicles. Thus, the hydrophobic regions of prebiotic vesicles and early cell membranes could have offered a refuge for this energetic molecule, increasing its lifetime in close proximity to the reactions for which it would be needed. This model of early energy storage evokes an additional critical function for the earliest cell membranes.

  14. Structural, optical and photo-catalytic activity of nanocrystalline NiO thin films

    SciTech Connect

    Al-Ghamdi, Attieh A.; Abdel-wahab, M. Sh.; Farghali, A.A.; Hasan, P.M.Z.

    2016-03-15

    Highlights: • Synthesis of nanocrystalline NiO thin films with different thicknesses using DC magnetron sputtering technique. • Effect of film thickness and particle size on photo-catalytic degradation of methyl green dye under UV light was studied. • The deposited NiO thin films are efficient, stable and possess high photo-catalytic activity upon reuse. - Abstract: Physical deposition of nanocrystalline nickel oxide (NiO) thin films with different thickness 30, 50 and 80 nm have been done on glass substrate by DC magnetron sputtering technique and varying the deposition time from 600, 900 to 1200 s. The results of surface morphology and optical characterization of these films obtained using different characterization techniques such as X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), photoluminescence (PL) and UV–vis spectrophotometry provide important information like formation of distinct nanostructures in different films and its effect on their optical band gap which has decreased from 3.74 to 3.37 eV as the film thickness increases. Most importantly these films have shown very high stability and a specialty to be recycled without much loss of their photo-catalytic activity, when tested as photo-catalysts for the degradation of methyl green dye (MG) from the wastewater under the exposure of 18 W energy of UV lamp.

  15. 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.

  16. Preparation of aluminum-containing mesoporous silica with hierarchical macroporous architecture and its enhanced catalytic activities.

    PubMed

    Kamegawa, Takashi; Tanaka, Shota; Seto, Hiroki; Zhou, Dayang; Yamashita, Hiromi

    2013-08-28

    Aluminum-containing mesoporous silica with hierarchical macroporous architecture (Al-MMS) was successfully prepared using a solvent evaporation method through the combination of precursor solution for synthesis of Al-containing mesoporous silica (Al-MS) and poly(methyl methacrylate) (PMMA) colloidal crystals as a hard template. The porous structure and the state of aluminum were investigated using various characterization techniques. The construction of combined structure of Al-MMS, i.e., hierarchical macroporous architecture consisting of thin mesoporous silica frameworks, led to the formation of many mesopore entrances and the shortening of the mesoporous channels. In the tetrahydropyranylation of linear alcohols with dihydropyran (DHP), Al-MMS exhibited higher catalytic activities for the formation of corresponding tetrahydropyranyl ethers as compared to Al-MS. The advantageous structure of Al-MMS enables the efficient transport of reactants to the catalytically active sites, which realizes the significant enhancement of catalytic performances in the reaction of DHP with alcohols having longer alkyl chains.

  17. Facile and green synthesis of cellulose nanocrystal-supported gold nanoparticles with superior catalytic activity.

    PubMed

    Yan, Wei; Chen, Chang; Wang, Ling; Zhang, Dan; Li, Ai-Jun; Yao, Zheng; Shi, Li-Yi

    2016-04-20

    The emphasis of science and technology shifts toward environmentally friendly and sustainable resources and processes. Herein, we report a facile, one-pot and green synthesis of biomaterial-supported gold nanoparticles (AuNPs) with superior catalytic activity. Cellulose nanocrystal (CNC)-supported AuNPs were prepared by heating the aqueous mixture of HAuCl4, CNCs and polyethylene glycol, avoiding toxic chemicals, extreme condition and complicated procedure. The resultant CNC-supported AuNPs exhibited catalytic activities for the reduction of 4-nitrophenol by sodium borohydride. The maximum apparent rate constant reached 1.47×10(-2)s(-1), and the turnover frequency reached 641h(-1). The superior catalytic performance can be ascribed to the large amount of highly dispersed AuNPs with few nanometers in size which are loaded on CNCs. About 90% of the AuNPs are smaller than 10nm, and nearly 60% of the AuNPs are smaller than 5nm. The synthesis is eco-friendly, facile and low-cost, thus has great potential for industrial and medical applications.

  18. 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

    2016-03-08

    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.

  19. Block copolymer hollow fiber membranes with catalytic activity and pH-response.

    PubMed

    Hilke, Roland; Pradeep, Neelakanda; Madhavan, Poornima; Vainio, Ulla; Behzad, Ali Reza; Sougrat, Rachid; Nunes, Suzana P; Peinemann, Klaus-Viktor

    2013-08-14

    We fabricated block copolymer hollow fiber membranes with self-assembled, shell-side, uniform pore structures. The fibers in these membranes combined pores able to respond to pH and acting as chemical gates that opened above pH 4, and catalytic activity, achieved by the incorporation of gold nanoparticles. We used a dry/wet spinning process to produce the asymmetric hollow fibers and determined the conditions under which the hollow fibers were optimized to create the desired pore morphology and the necessary mechanical stability. To induce ordered micelle assembly in the doped solution, we identified an ideal solvent mixture as confirmed by small-angle X-ray scattering. We then reduced p-nitrophenol with a gold-loaded fiber to confirm the catalytic performance of the membranes.

  20. 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.

  1. A very active cu-catalytic system for the synthesis of aryl, heteroaryl, and vinyl sulfides.

    PubMed

    Kabir, M Shahjahan; Lorenz, Michael; Van Linn, Michael L; Namjoshi, Ojas A; Ara, Shamim; Cook, James M

    2010-06-04

    cis-1,2-Cyclohexanediol (L3) has been shown to be an efficient and versatile bidentate O-donor ligand that provides a highly active Cu-catalytic system. It was more effective than diols such as trans-1,2-cyclohexanediol or ethylene glycol. This commercially available cis-1,2-cyclohexanediol ligand facilitated the Cu-catalyzed cross-coupling reactions of alkyl, aryl, or heterocyclic thiols with either alkyl, aryl, heterocyclic, or substituted vinyl halides. This new catalytic system promoted the mild and efficient stereo- and regiospecific synthesis of biologically important vinyl sulfides. The yields obtained using electron-rich substituted vinyl sulfides with this catalyst system are generally 75-98%. Most importantly, this singular catalyst system is extremely versatile and provides entry into a wide range of sulfides. This method is particularly noteworthy given its mild reaction conditions, simplicity, generality, and exceptional level of functional group tolerance.

  2. Graphdiyne oxides as excellent substrate for electroless deposition of Pd clusters with high catalytic activity.

    PubMed

    Qi, Hetong; Yu, Ping; Wang, Yuexiang; Han, Guangchao; Liu, Huibiao; Yi, Yuanping; Li, Yuliang; Mao, Lanqun

    2015-04-29

    Graphdiyne (GDY), a novel kind of two-dimensional carbon allotrope consisting of sp- and sp(2)-hybridized carbon atoms, is found to be able to serve as the reducing agent and stabilizer for electroless deposition of highly dispersed Pd nanoparticles owing to its low reduction potential and highly conjugated electronic structure. Furthermore, we observe that graphdiyne oxide (GDYO), the oxidation form of GDY, can be used as an even excellent substrate for electroless deposition of ultrafine Pd clusters to form Pd/GDYO nanocomposite that exhibits a high catalytic performance toward the reduction of 4-nitrophenol. The high catalytic performance is considered to benefit from the rational design and electroless deposition of active metal catalysts with GDYO as the support.

  3. Saccharomyces cerevisiae DNA ligase IV supports imprecise end joining independently of its catalytic activity.

    PubMed

    Chiruvella, Kishore K; Liang, Zhuobin; Birkeland, Shanda R; Basrur, Venkatesha; Wilson, Thomas E

    2013-06-01

    DNA ligase IV (Dnl4 in budding yeast) is a specialized ligase used in non-homologous end joining (NHEJ) of DNA double-strand breaks (DSBs). Although point and truncation mutations arise in the human ligase IV syndrome, the roles of Dnl4 in DSB repair have mainly been examined using gene deletions. Here, Dnl4 catalytic point mutants were generated that were severely defective in auto-adenylation in vitro and NHEJ activity in vivo, despite being hyper-recruited to DSBs and supporting wild-type levels of Lif1 interaction and assembly of a Ku- and Lif1-containing complex at DSBs. Interestingly, residual levels of especially imprecise NHEJ were markedly higher in a deletion-based assay with Dnl4 catalytic mutants than with a gene deletion strain, suggesting a role of DSB-bound Dnl4 in supporting a mode of NHEJ catalyzed by a different ligase. Similarly, next generation sequencing of repair joints in a distinct single-DSB assay showed that dnl4-K466A mutation conferred a significantly different imprecise joining profile than wild-type Dnl4 and that such repair was rarely observed in the absence of Dnl4. Enrichment of DNA ligase I (Cdc9 in yeast) at DSBs was observed in wild-type as well as dnl4 point mutant strains, with both Dnl4 and Cdc9 disappearing from DSBs upon 5' resection that was unimpeded by the presence of catalytically inactive Dnl4. These findings indicate that Dnl4 can promote mutagenic end joining independently of its catalytic activity, likely by a mechanism that involves Cdc9.

  4. 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.

  5. Functional analyses for tRNase Z variants: an aspartate and a histidine in the active site are essential for the catalytic activity.

    PubMed

    Elbarbary, Reyad A; Takaku, Hiroaki; Nashimoto, Masayuki

    2008-12-01

    We performed functional analyses for various single amino-acid substitution variants of Escherichia coli, Bacillus subtilis, and human tRNase Zs. The well-conserved six histidine, His(I)-His(VI), and two aspartate, Asp(I) and Asp(II), residues together with metal ions are thought to form the active site of tRNase Z. The Mn(2+)-rescue analysis for Thermotoga maritima tRNase Z(S) has suggested that Asp(I) and His(V) directly contribute the proton transfer for the catalysis, and a catalytic mechanism has been proposed. However, experimental evidence supporting the proposed mechanism was limited. Here we intensively examined E. coli and B. subtilis tRNase Z(S) variants and human tRNase Z(L) variants for cleavage activities on pre-tRNAs in the presence of Mg(2+) or Mn(2+) ions. We observed that the Mn(2+) ions cannot rescue the activities of Asp(I)Ala and His(V)Ala variants from each species, which are lost in the presence of Mg(2+). This observation may support the proposed catalytic mechanism.

  6. pH-susceptibility of HLA-DO tunes DO/DM ratios to regulate HLA-DM catalytic activity

    PubMed Central

    Jiang, Wei; Strohman, Michael J.; Somasundaram, Sriram; Ayyangar, Sashi; Hou, Tieying; Wang, Nan; Mellins, Elizabeth D.

    2015-01-01

    The peptide-exchange catalyst, HLA-DM, and its inhibitor, HLA-DO control endosomal generation of peptide/class II major histocompatibility protein (MHC-II) complexes; these complexes traffic to the cell surface for inspection by CD4+ T cells. Some evidence suggests that pH influences DO regulation of DM function, but pH also affects the stability of polymorphic MHC-II proteins, spontaneous peptide loading, DM/MHC-II interactions and DM catalytic activity, imposing challenges on approaches to determine pH effects on DM-DO function and their mechanistic basis. Using optimized biochemical methods, we dissected pH-dependence of spontaneous and DM-DO-mediated class II peptide exchange and identified an MHC-II allele-independent relationship between pH, DO/DM ratio and efficient peptide exchange. We demonstrate that active, free DM is generated from DM-DO complexes at late endosomal/lysosomal pH due to irreversible, acid-promoted DO destruction rather than DO/DM molecular dissociation. Any soluble DM that remains in complex with DO stays inert. pH-exposure of DM-DO in cell lysates corroborates such a pH-regulated mechanism, suggesting acid-activated generation of functional DM in DO-expressing cells. PMID:26610428

  7. DNA binding residues in the RQC domain of Werner protein are critical for its catalytic activities.

    PubMed

    Tadokoro, Takashi; Kulikowicz, Tomasz; Dawut, Lale; Croteau, Deborah L; Bohr, Vilhelm A

    2012-06-01

    Werner protein (WRN), member of the RecQ helicase family, is a helicase and exonuclease, and participates in multiple DNA metabolic processes including DNA replication, recombination and DNA repair. Mutations in the WRN gene cause Werner syndrome, associated with premature aging, genome instability and cancer predisposition. The RecQ C-terminal (RQC) domain of WRN, containing α2-α3 loop and β-wing motifs, is important for DNA binding and for many protein interactions. To better understand the critical functions of this domain, we generated recombinant WRN proteins (using a novel purification scheme) with mutations in Arg-993 within the α2-α3 loop of the RQC domain and in Phe-1037 of the -wing motif. We then studied the catalytic activities and DNA binding of these mutant proteins as well as some important functional protein interactions. The mutant proteins were defective in DNA binding and helicase activity, and interestingly, they had deficient exonuclease activity and strand annealing function. The RQC domain of WRN has not previously been implicated in exonuclease or annealing activities. The mutant proteins could not stimulate NEIL1 incision activity as did the wild type. Thus, the Arg-993 and Phe-1037 in the RQC domain play essential roles in catalytic activity, and in functional interactions mediated by WRN.

  8. Effects of detergents on catalytic activity of human endometase/matrilysin 2, a putative cancer biomarker.

    PubMed

    Park, Hyun I; Lee, Seakwoo; Ullah, Asad; Cao, Qiang; Sang, Qing-Xiang Amy

    2010-01-15

    Matrix metalloproteinases (MMPs) are a family of hydrolytic enzymes that play significant roles in development, morphogenesis, inflammation, and cancer invasion. Endometase (matrilysin 2 or MMP-26) is a putative early biomarker for human carcinomas. The effects of the ionic and nonionic detergents on catalytic activity of endometase were investigated. The hydrolytic activity of endometase was detergent concentration dependent, exhibiting a bell-shaped curve with its maximum activity near the critical micelle concentration (CMC) of nonionic detergents tested. The effect of Brij-35 on human gelatinase B (MMP-9), matrilysin (MMP-7), and membrane-type 1 MMP (MT1-MMP) was further explored. Their maximum catalysis was observed near the CMC of Brij-35 ( approximately 90muM). Their IC(50) values were above the CMC. The inhibition mechanism of MMP-7, MMP-9, and MT1-MMP by Brij-35 was a mixed type as determined by Dixon's plot; however, the inhibition mechanism of endometase was noncompetitive with a K(i) value of 240muM. The catalytic activities of MMPs are influenced by detergents. Monomer of detergents may activate and stabilize MMPs to enhance catalysis, but micelle of detergents may sequester enzyme and block the substrate binding site to impede catalysis. Under physiological conditions, a lipid or membrane microenvironment may regulate enzymatic activity.

  9. 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.

  10. 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

  11. A comparative study of alumina-supported Ni catalysts prepared by photodeposition and impregnation methods on the catalytic ozonation of 2,4-dichlorophenoxyacetic acid

    NASA Astrophysics Data System (ADS)

    Rodríguez, Julia L.; Valenzuela, Miguel A.; Tiznado, Hugo; Poznyak, Tatiana; Chairez, Isaac; Magallanes, Diana

    2017-02-01

    The heterogeneous catalytic ozonation on unsupported and supported oxides has been successfully tested for the removal of several refractory compounds in aqueous solution. In this work, alumina-supported nickel catalysts prepared by photodeposition and impregnation methods were compared in the catalytic ozonation of 2,4-dichlorophenoxyacetic acid (2,4-D). The catalysts were characterized by high-resolution electron microscopy and X-ray photoelectron spectroscopy. The photochemical decomposition of Ni acetylacetonate to produce Ni(OH)2, NiO, and traces of Ni° deposited on alumina was achieved in the presence of benzophenone as a sensitizer. A similar surface composition was found with the impregnated catalyst after its reduction with hydrogen at 500 °C and exposed to ambient air. Results indicated a higher initial activity and maleic acid (byproduct) concentration with the photodeposited catalyst (1 wt% Ni) compared to the impregnated catalyst (3 wt% Ni). These findings suggest the use of the photodeposition method as a simple and reliable procedure for the preparation of supported metal oxide/metal catalysts under mild operating conditions.

  12. Catalytic and ligand binding properties of the FK506 binding protein FKBP12: effects of the single amino acid substitution of Tyr82 to Leu.

    PubMed Central

    Bossard, M J; Bergsma, D J; Brandt, M; Livi, G P; Eng, W K; Johnson, R K; Levy, M A

    1994-01-01

    The binding of FK506 and rapamycin to their cytosolic receptor FKBP12 is an intermediate step in the paths leading to their potent immunosuppressive properties. One of the amino acids defining the hydrophobic binding cleft for the macrocycles is Tyr82, which is thought to form a hydrogen bond with the amide oxygens of the common pipecolyl structural element within the two macrolides. To understand better the influence of this amino acid residue in catalytic activity (cis-trans peptidyl prolyl isomerization) and ligand binding properties, a Tyr82 to Leu site-specific modification of FKBP12 was prepared, purified and characterized. Kinetic experiments have demonstrated that the Tyr82 to Leu modification has a greater effect on catalytic properties than on ligand binding affinities, a result which indicates that these inhibitors may not be binding as true transition-state analogues. In an additional test for cellular function, expression of both wild-type and mutant human FKBP12 in a strain of Saccharomyces cerevisiae rendered resistant to rapamycin by deletion of the gene encoding a cytosolic rapamycin binding protein (RPB1), the yeast homologue of FKBP12, restored wild-type drug sensitivity. PMID:7507662

  13. Catalytic oxidation of pulping effluent by activated carbon-supported heterogeneous catalysts.

    PubMed

    Yadav, Bholu Ram; Garg, Anurag

    2016-01-01

    The present study deals with the non-catalytic and catalytic wet oxidation (CWO) for the removal of persistent organic compounds from the pulping effluent. Two activated carbon-supported heterogeneous catalysts (Cu/Ce/AC and Cu/Mn/AC) were used for CWO after characterization by the following techniques: temperature-programmed reduction, Fourier transform infrared spectroscopy and thermo-gravimetric analysis. The oxidation reaction was performed in a batch high-pressure reactor (capacity = 0.7  L) at moderate oxidation conditions (temperature = 190°C and oxygen pressure = 0.9 MPa). With Cu/Ce/AC catalyst, the maximum chemical oxygen demand (COD), total organic carbon (TOC) and lignin removals of 79%, 77% and 88% were achieved compared to only 50% removal during the non-catalytic process. The 5-day biochemical oxygen demand (BOD5) to COD ratio (a measure for biodegradability) of the pulping effluent was improved to 0.52 from an initial value of 0.16. The mass balance calculations for solid recovered after CWO reaction showed 8% and 10% deduction in catalyst mass primarily attributed to the loss of carbon and metal leaching. After the CWO process, carbon deposition was also observed on the recovered catalyst which was responsible for around 3-4% TOC reduction.

  14. 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

  15. Dynamic formation of single-atom catalytic active sites on ceria-supported gold nanoparticles

    DOE PAGES

    Wang, Yanggang; Mei, Donghai; Glezakou, Vassiliki Alexandra; ...

    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

  16. 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.

  17. 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.

  18. [The state of phospholipase D in solution and its catalytic activity].

    PubMed

    Rakhimov, M M; Mad'iarov, Sh R

    1977-04-01

    Functioning of water-soluble phospholipase D from cotton seeds is studied on two phases contact area (liquid-liquid, liquid-solid substance) and on the surface of mixed lecitine and sodium dodecylsulphate micelles. It is found that water-soluble phospholipase D, which normally has no catalytic activity, is capable to hydrolyse its substrates in the presence of organic solvents, solid adsorbents and sodium dodecylsulphate. The data obtained show that in all the cases studied the activation observed is due to adsorption immobilization of the enzyme. K lambda and K alpha constants are introduced, which are characteristics of immobilyzing ability of agents-matrices for immobilization. Phase transitions, which take place in heterogenous system (enzyme-activator-substrate-water solution), are found to be a necessary condition for the enzyme activation. A hypothesis, that catalytical activity of water-soluble phospholipase D is inherent of the adsorbed enzyme, is discussed on the basis of the data on comparative study of adsorbed and water-soluble enzymes.

  19. 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.

  20. 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…

  1. Synthetically Tuned Atomic Ordering in PdCu Nanoparticles with Enhanced Catalytic Activity toward Solvent-Free Benzylamine Oxidation.

    PubMed

    Marakatti, Vijaykumar S; Sarma, Saurav Ch; Joseph, Boby; Banerjee, Dipanjan; Peter, Sebastian C

    2017-02-01

    Synthesis of ordered compounds with nano size is of particular interest for tuning the surface properties with enhanced activity and selectivity toward various important industrial catalytic processes. In this work, we synthesized ordered PdCu nanoparticles as highly efficient catalyst for the solvent-free aerobic oxidation of benzylamine. The PdxCu1-x catalysts with different chemical compositions (x = 0, 0.25, 0.4, 0.5, 0.6, 0.75, 1) were prepared by polyol method using NaBH4 as a reducing agent and were well-characterized by X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) energy-dispersive analysis of X-rays, and X-ray absorption fine structure. The effect of different metal concentrations of Pd and Cu on the formation of PdxCu1-x nanoparticles was investigated. The XRD and TEM confirmed the formation of ordered PdCu intermetallic phase with body-centered cubic (BCC) structure for the synthetic composition of Pd/Cu = 1:1. For compositions x = 0, 0.25, 0.75, and 1, PdxCu1-x alloy with face-centered cubic (FCC) structure was observed, whereas mixed phase of BCC and FCC was observed for x = 0.4 and 0.6. The use of strong reducing agent (NaBH4) was essential to synthesize PdCu ordered phase compared to weak reducing agents such as oleylamine and ascorbic acid. The PdCu nanocatalyst with ordered structure (BCC) showed excellent catalytic activity compared to PdxCu1-x alloy nanoparticles with FCC structure. The atomic ordering in the PdCu intermetallic was the driving force for the enhancement in the catalytic activity with high benzylamine conversion of 94.0% and dibenzylimine selectivity of 92.2% compared to its monometallic and alloy counterparts. Moreover, ordered PdCu alloy showed good recyclability and activity toward the oxidation of different amines.

  2. Influence of the preparation procedure on the catalytic activity of gold supported on diamond nanoparticles for phenol peroxidation.

    PubMed

    Martin, Roberto; Navalon, Sergio; Delgado, Juan Jose; Calvino, Jose J; Alvaro, Mercedes; Garcia, Hermenegildo

    2011-08-16

    The catalytic activity of diamond-supported gold nanoparticle (Au/D) samples prepared by the deposition/precipitation method have been correlated as a function of the pH and the reduction treatment. It was found that the most active material is the one prepared at pH 5 followed by subsequent thermal treatment at 300 °C under hydrogen. TEM images show that Au/D prepared under optimal conditions contain very small gold nanoparticles with sizes below 2 nm that are proposed to be responsible for the catalytic activity. Tests of productivity using large phenol (50 g L(-1)) and H(2)O(2) excesses (100 g L(-1)) and reuse gives a minimum TON of 458,759 moles of phenol degraded per gold atom. Analysis of the organic compounds extracted from the deactivated solid catalyst indicates that the poisons are mostly hydroxylated dicarboxylic acids arising from the degradative oxidation of the phenyl ring. By determining the efficiency for phenol degradation and the amount of O(2) evolved two different reactions of H(2)O(2) decomposition (the Fenton reaction at acidic pH values and spurious O(2) evolution at basic pH values) are proposed for Au/D catalysis. The activation energy of the two processes is very similar (ranging between 30 and 35 kJ mol(-1)). By using dimethylsulfoxide as a radical scavenger and N-tert-butyl-α-phenylnitrone as a spin trap under aerated conditions, the EPR spectrum of the expected PBN-OCH(3) adduct was detected, supporting the generation of HO(.), characteristic of Fenton chemistry in the process. Phenol degradation, on the other hand, exhibits the same activation energy as H(2)O(2) decomposition at pH 4 (due to the barrierless attack of HO(.) to phenol), but increases the activation energy gradually up to about 90 kJ mol(-1) at pH 7 and then undergoes a subsequent reduction as the pH increases reaching another minimum at pH 8.5 (49 kJ mol(-1)).

  3. 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.

  4. Development of a novel catalytic amyloid displaying a metal-dependent ATPase-like activity.

    PubMed

    Monasterio, Octavio; Nova, Esteban; Diaz-Espinoza, Rodrigo

    2017-01-22

    Amyloids are protein aggregates of highly regular structure that are involved in diverse pathologies such as Alzheimer's and Parkinson's disease. Recent evidence has shown that under certain conditions, small peptides can self-assemble into amyloids that exhibit catalytic reactivity towards certain compounds. Here we report a novel peptide with a sequence derived from the active site of RNA polymerase that displays hydrolytic activity towards ATP. The catalytic reaction proceeds in the presence of the divalent metal manganese and the products are ADP and AMP. The kinetic data shows a substrate-dependent saturation of the activity with a maximum rate achieved at around 1 mM ATP. At higher ATP concentrations, we also observed substrate inhibition of the activity. The self-assembly of the peptide into amyloids is strictly metal-dependent and required for the catalysis. Our results show that aspartate-containing amyloids can also be catalysts under conditions that include interactions with metals. Moreover, we show for the first time an amyloid that exerts reactivity towards a biologically essential molecule.

  5. Activity, Expression and Function of a Second Drosophila Protein Kinase a Catalytic Subunit Gene

    PubMed Central

    Melendez, A.; Li, W.; Kalderon, D.

    1995-01-01

    The DC2 gene was isolated previously on the basis of sequence similarity to DCO, 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 did not affect the viability or phenotype of imaginal disc cells lacking DC0 activity or embryonic hatching of animals with reduced DC0 activity. Furthermore, transgenes expressing DC2 from a DC0 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. PMID:8601490

  6. Creation of catalytically active particles from enzymes crosslinked with a natural bifunctional agent--homocysteine thiolactone.

    PubMed

    Stroylova, Yulia Y; Semenyuk, Pavel I; Asriyantz, Regina A; Gaillard, Cedric; Haertlé, Thomas; Muronetz, Vladimir I

    2014-09-01

    The current study describes an approach to creation of catalytically active particles with increased stability from enzymes by N-homocysteinylation, a naturally presented protein modification. Enzymatic activities and properties of two globular tetrameric enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase (LDH) were studied before and after N-homocysteinylation. Modification of these proteins concerns the accessible lysine residues and introduces an average of 2-2,5 homocysteine residues per protein monomer. Formation of a range of aggregates was observed for both enzymes, which assemble via formation of intermolecular noncovalent bonds and by disulfide bonds. It was demonstrated that both studied enzymes retain their catalytic activities on modification and the subsequent formation of oligomeric forms. At low concentrations of homocysteine thiolactone, modification of GAPDH leads not only to prevention of spontaneous inactivation but also increases thermal stability of this enzyme on heating to 80°C. A moderate reduction of the activity of GAPDH observed in case of its crosslinking with 50-fold excess of homocysteine thiolactone per lysine is probably caused by hindered substrate diffusion. Spherical particles of 100 nm and larger diameters were observed by transmission electron microscopy and atomic force microscope techniques after modification of GAPDH with different homocysteine thiolactone concentrations. In case of LDH, branched fibril-like aggregates were observed under the same conditions. Interestingly, crosslinked samples of both proteins were found to have reversible thermal denaturation profiles, indicating that modification with homocysteine thiolactone stabilizes the spatial structure of these enzymes.

  7. 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

  8. Functional role of TRIM E3 ligase oligomerization and regulation of catalytic activity.

    PubMed

    Koliopoulos, Marios G; Esposito, Diego; Christodoulou, Evangelos; Taylor, Ian A; Rittinger, Katrin

    2016-06-01

    TRIM E3 ubiquitin ligases regulate a wide variety of cellular processes and are particularly important during innate immune signalling events. They are characterized by a conserved tripartite motif in their N-terminal portion which comprises a canonical RING domain, one or two B-box domains and a coiled-coil region that mediates ligase dimerization. Self-association via the coiled-coil has been suggested to be crucial for catalytic activity of TRIMs; however, the precise molecular mechanism underlying this observation remains elusive. Here, we provide a detailed characterization of the TRIM ligases TRIM25 and TRIM32 and show how their oligomeric state is linked to catalytic activity. The crystal structure of a complex between the TRIM25 RING domain and an ubiquitin-loaded E2 identifies the structural and mechanistic features that promote a closed E2~Ub conformation to activate the thioester for ubiquitin transfer allowing us to propose a model for the regulation of activity in the full-length protein. Our data reveal an unexpected diversity in the self-association mechanism of TRIMs that might be crucial for their biological function.

  9. 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.

  10. 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

  11. Almond shell activated carbon: adsorbent and catalytic support in the phenol degradation.

    PubMed

    Omri, Abdessalem; Benzina, Mourad

    2014-06-01

    In this work, two technologies are studied for the removal of phenol from aqueous solution: dynamic adsorption onto activated carbon and photocatalysis. Almond shell activated carbon (ASAC) was used as adsorbent and catalytic support in the phenol degradation process. The prepared catalyst by deposition of anatase TiO2 on the surface of activated carbon was characterized by scanning electron microscopy, sorption of nitrogen, X-ray diffraction, Fourier transform infrared (FT-IR) spectroscopy, and pHZPC point of zero charge. In the continuous adsorption experiments, the effects of flow rate, bed height, and solution temperature on the breakthrough curves have been studied. The breakthrough curves were favorably described by the Yoon-Nelson model. The photocatalytic degradation of phenol has been investigated at room temperature using TiO2-coated activated carbon as photocatalyst (TiO2/ASAC). The degradation reaction was optimized with respect to the phenol concentration and catalyst amount. The kinetics of disappearance of the organic pollutant followed an apparent first-order rate. The findings demonstrated the applicability of ASAC for the adsorptive and catalytic treatment of phenol.

  12. A comparison of different activated carbon performances on catalytic ozonation of a model azo reactive dye.

    PubMed

    Gül, S; Eren, O; Kır, S; Onal, Y

    2012-01-01

    The objective of this study is to compare the performances of catalytic ozonation processes of two activated carbons prepared from olive stone (ACOS) and apricot stone (ACAS) with commercial ones (granular activated carbon-GAC and powder activated carbon-PAC) in degradation of reactive azo dye (Reactive Red 195). The optimum conditions (solution pH and amount of catalyst) were investigated by using absorbencies at 532, 220 and 280 nm wavelengths. Pore properties of the activated carbon (AC) such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by N(2) adsorption. The highest BET surface area carbon (1,275 m(2)/g) was obtained from ACOS with a particle size of 2.29 nm. After 2 min of catalytic ozonation, decolorization performances of ACOS and ACAS (90.4 and 91.3%, respectively) were better than that of GAC and PAC (84.6 and 81.2%, respectively). Experimental results showed that production of porous ACs with high surface area from olive and apricot stones is feasible in Turkey.

  13. 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

  14. 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...

  15. [Peptide hydrolases with catalytic dyad Ser-Lys. Similarity and distinctions of the active centers of ATP-dependent Lon proteases, LexA repressors, signal peptidases and C-terminal processing proteases].

    PubMed

    Rotanova, T V

    2002-01-01

    It is established that ATP-dependent protease Lon family belongs to the serine-lysine peptide hydrolases clan. Significant similarity of amino acid sequences of proteases Lon and repressors LexA in the regions including the catalytic serine and lysine residues is revealed by comparing primary structures of different families of the enzymes with Ser-Lys catalytic dyad. The both Lon and LexA families are shown to be divided into two subfamilies in accordance with the nature of amino acids in the catalytically active serine environment. Putative DNA binding sites are revealed in proteolytic domains of Lon A subfamily. Similarities and distinctions of the all families peptide hydrolases of the clan in the regions of their active centers are discussed.

  16. 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.

  17. The roles of active site residues in the catalytic mechanism of methylaspartate ammonia-lyase.

    PubMed

    Raj, Hans; Poelarends, Gerrit J

    2013-01-01

    Methylaspartate ammonia-lyase (MAL; EC 4.3.1.2) catalyzes the reversible addition of ammonia to mesaconate to yield l-threo-(2S,3S)-3-methylaspartate and l-erythro-(2S,3R)-3-methylaspartate as products. In the proposed minimal mechanism for MAL of Clostridium tetanomorphum, Lys-331 acts as the (S)-specific base catalyst and abstracts the 3S-proton from l-threo-3-methylaspartate, resulting in an enolate anion intermediate. This enolic intermediate is stabilized by coordination to the essential active site Mg(2+) ion and hydrogen bonding to the Gln-329 residue. Collapse of this intermediate results in the release of ammonia and the formation of mesaconate. His-194 likely acts as the (R)-specific base catalyst and abstracts the 3R-proton from the l-erythro isomer of 3-methylaspartate, yielding the enolic intermediate. In the present study, we have investigated the importance of the residues Gln-73, Phe-170, Gln-172, Tyr-356, Thr-360, Cys-361 and Leu-384 for the catalytic activity of C. tetanomorphum MAL. These residues, which are part of the enzyme surface lining the substrate binding pocket, were subjected to site-directed mutagenesis and the mutant enzymes were characterized for their structural integrity, ability to catalyze the amination of mesaconate, and regio- and diastereoselectivity. Based on the observed properties of the mutant enzymes, combined with previous structural studies and protein engineering work, we propose a detailed catalytic mechanism for the MAL-catalyzed reaction, in which the side chains of Gln-73, Gln-172, Tyr-356, Thr-360, and Leu-384 provide favorable interactions with the substrate, which are important for substrate binding and activation. This detailed knowledge of the catalytic mechanism of MAL can serve as a guide for future protein engineering experiments.

  18. Biorecovery of gold as nanoparticles and its catalytic activities for p-nitrophenol degradation.

    PubMed

    Zhu, Nengwu; Cao, Yanlan; Shi, Chaohong; Wu, Pingxiao; Ma, Haiqin

    2016-04-01

    Recovery of gold from aqueous solution using simple and economical methodologies is highly desirable. In this work, recovery of gold as gold nanoparticles (AuNPs) by Shewanella haliotis with sodium lactate as electron donor was explored. The results showed that the process was affected by the concentration of biomass, sodium lactate, and initial gold ions as well as pH value. Specifically, the presence of sodium lactate determines the formation of nanoparticles, biomass, and AuCl4 (-) concentration mainly affected the size and dispersity of the products, reaction pH greatly affected the recovery efficiency, and morphology of the products in the recovery process. Under appropriate conditions (5.25 g/L biomass, 40 mM sodium lactate, 0.5 mM AuCl4 (-), and pH of 5), the recovery efficiency was almost 99 %, and the recovered AuNPs were mainly spherical with size range of 10-30 nm (~85 %). Meanwhile, Fourier transforms infrared spectroscopy and X-ray photoelectron spectroscopy demonstrated that carboxyl and amine groups might play an important role in the process. In addition, the catalytic activity of the AuNPs recovered under various conditions was testified by analyzing the reduction rate of p-nitrophenol by borohydride. The biorecovered AuNPs exhibited interesting size and shape-dependent catalytic activity, of which the spherical particle with smaller size showed the highest catalytic reduction activity with rate constant of 0.665 min(-1).

  19. Possible role of inter-domain salt bridges in oligopeptidase B from Trypanosoma brucei: critical role of Glu172 of non-catalytic β-propeller domain in catalytic activity and Glu490 of catalytic domain in stability of OPB.

    PubMed

    Fukumoto, Junki; Ismail, Nor Ismaliza Mohd; Kubo, Masaki; Kinoshita, Keita; Inoue, Masahiro; Yuasa, Keizo; Nishimoto, Makoto; Matsuki, Hitoshi; Tsuji, Akihiko

    2013-11-01

    Oligopeptidase B (OPB) is a member of the prolyl oligopeptidase (POP) family of serine proteases. OPB in trypanosomes is an important virulence factor and potential pharmaceutical target. Characteristic structural features of POP family members include lack of a propeptide and presence of a β-propeller domain (PD), although the role of the β-PD has yet to be fully understood. In this work, residues Glu(172), Glu(490), Glu(524) and Arg(689) in Trypanosoma brucei OPB (Tb OPB), which are predicted to form inter-domain salt bridges, were substituted for Gln and Ala, respectively. These mutants were evaluated in terms of catalytic properties and stability. A negative effect on kcat/Km was obtained following mutation of Glu(172) or Arg(689). In contrast, the E490Q mutant exhibited markedly decreased thermal stability, although this mutation had less effect on catalytic properties compared to the E172Q and R689A mutants. Trypsin digestion showed that the boundary regions between the β-PD and catalytic domains (CDs) of the E490Q mutant are unfolded with heat treatment. These results indicated that Glu(490) in the CD plays a role in stabilization of Tb OPB, whereas Glu(172) in the β-PD is critical for the catalytic activity of Tb OPB.

  20. 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.

  1. 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.

  2. 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.

  3. Catalytic, oxidative condensation of CH4 to CH3COOH in one step via CH activation.

    PubMed

    Periana, Roy A; Mironov, Oleg; Taube, Doug; Bhalla, Gaurav; Jones, C J

    2003-08-08

    Acetic acid is an important petrochemical that is currently produced from methane (or coal) in a three-step process based on carbonylation of methanol. We report a direct, selective, oxidative condensation of two methane molecules to acetic acid at 180 degrees C in liquid sulfuric acid. Carbon-13 isotopic labeling studies show that both carbons of acetic acid originate from methane. The reaction is catalyzed by palladium, and the results are consistent with the reaction occurring by tandem catalysis, involving methane C-H activation to generate Pd-CH3 species, followed by efficient oxidative carbonylation with methanol, generated in situ from methane, to produce acetic acid.

  4. Characterization and catalytic activity of Cu Co spinel thin films catalysts

    NASA Astrophysics Data System (ADS)

    Stefanov, P.; Avramova, I.; Stoichev, D.; Radic, N.; Grbic, B.; Marinova, Ts.

    2005-05-01

    The Cu-Co mixed oxide catalysts were prepared on a La 2O 3/ZrO 2/SS support by thermal decomposition of nitrate precursors. The catalyst samples were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectrum (XPS) and Brunauer-Emmet-Teller (BET) surface area. The XPS data indicated the formation of some amount of CuO together with the Cu-Co spinel after annealing at 550 °C. The Cu-Co/ZrO 2/SS thin film catalysts were tested for three-way catalytic performance and showed moderate activity.

  5. Synthesis, characterization and catalytic activity of novel large network polystyrene-immobilized organic bases

    DOE PAGES

    Tassi, Marco; Bartollini, Elena; Adriaensens, Peter; ...

    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.

  6. Metal-Organic Frameworks derivatives for improving the catalytic activity of CO oxidation reaction.

    PubMed

    Ji, Wenlan; Xu, Zhiling; Liu, Pengfei; Zhang, Suoying; Zhou, Weiqiang; Li, Hongfeng; Zhang, Tao; Li, Linjie; Lu, Xiaohua; Wu, Jiansheng; Zhang, Weina; Huo, Fengwei

    2017-03-15

    Metal-Organic Frameworks (MOFs) based derivatives have attracted an increasing interest in various research fields. However, most of reported papers mainly focused on the pristine MOFs-based derivatives, and researches on the functional MOFs-based derivatives composites are rare. Here, a simple strategy was reported to design the functional MOFs based derivatives composites by the encapsulation of the metal nanoparticles (MNPs) in MOFs matrixes (MNPs@MOFs) and the high-temperature calcination of MNPs@MOFs composites. The as-prepared MNPs@metal oxide composites with the hierarchical pore structure exhibited excellent catalytic activity and high stability for CO oxidation reaction.

  7. 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.

  8. 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

  9. 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.

  10. Differential activation of pregnane X receptor by carnosic acid, carnosol, ursolic acid, and rosmarinic acid.

    PubMed

    Seow, Chun Ling; Lau, Aik Jiang

    2017-03-10

    Pregnane X receptor (PXR) regulates the expression of many genes, including those involved in drug metabolism and transport, and has been linked to various diseases, including inflammatory bowel disease. In the present study, we determined whether carnosic acid and other chemicals in rosemary extract (carnosol, ursolic acid, and rosmarinic acid) are PXR activators. As assessed in dual-luciferase reporter gene assays, carnosic acid, carnosol, and ursolic acid, but not rosmarinic acid, activated human PXR (hPXR) and mouse PXR (mPXR), whereas carnosol and ursolic acid, but not carnosic acid or rosmarinic acid, activated rat PXR (rPXR). Dose-response experiments indicated that carnosic acid, carnosol, and ursolic acid activated hPXR with EC50 values of 0.79, 2.22, and 10.77μM, respectively. Carnosic acid, carnosol, and ursolic acid, but not rosmarinic acid, transactivated the ligand-binding domain of hPXR and recruited steroid receptor coactivator-1 (SRC-1), SRC-2, and SRC-3 to the ligand-binding domain of hPXR. Carnosic acid, carnosol, and ursolic acid, but not rosmarinic acid, increased hPXR target gene expression, as shown by an increase in CYP3A4, UGT1A3, and ABCB1 mRNA expression in LS180 human colon adenocarcinoma cells. Rosmarinic acid did not attenuate the extent of hPXR activation by rifampicin, suggesting it is not an antagonist of hPXR. Overall, carnosic acid, carnosol, and ursolic acid, but not rosmarinic acid, are hPXR agonists, and carnosic acid shows species-dependent activation of hPXR and mPXR, but not rPXR. The findings provide new mechanistic insight on the effects of carnosic acid, carnosol, and ursolic acid on PXR-mediated biological effects.

  11. Factor IX Amagasaki: A new mutation in the catalytic domain resulting in the loss of both coagulant and esterase activities

    SciTech Connect

    Miyata, Toshiyuki; Iwanaga, Sadaaki ); Sakai, Toshiyuki; Sugimoto, Mitsuhiko; Naka, Hiroyuki; Yamamoto, Kazukuni; Yoshioka, Akira; Fukui, Hiromu ); Mitsui, Kotoko; Kamiya, Kensyu; Umeyama, Hideaki )

    1991-11-26

    Factor IX Amagasaki (AMG) is a naturally occurring mutant of factor IX having essentially no coagulant activity, even though normal levels of antigen are detected in plasma. Factor IX AMG was purified from the patient's plasma by immunoaffinity chromatography with an anti-factor IX monoclonal antibody column. Factor IX AMG was cleaved normally by factor VIIa-tissue factor complex, yielding a two-chain factor IXa. Amino acid composition and sequence analysis of one of the tryptic peptides isolated from factor IX AMG revealed that Gly-311 had been replaced by Glu. The authors identified a one-base substitution of guanine to adenine in exon VIII by amplifying exon VIII using the polymerase chain reaction method and sequencing the product. This base mutation also supported the replacement of Gly-311 by Glu. In the purified system, factor IXa AMG did not activate for factor X in the presence of factor VIII, phospholipids, and Ca{sup 2+}, and no esterase activity toward Z-Arg-p-nitrobenzyl ester was observed. The model building of the serine protease domain of factor IXa suggests that the Gly-311 {yields} Glu exchange would disrupt the specific conformational state in the active site environment, resulting in the substrate binding site not forming properly. This is the first report to show the experimental evidence for importance of a highly conserved Gly-142 (chymotrypsinogen numbering) located in the catalytic site of mammalian serine proteases so far known.

  12. 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.

  13. Catalytic destruction of chloramine to nitrogen using chlorination and activated carbon--case study.

    PubMed

    Kochany, J; Lipczynska-Kochany, E

    2008-04-01

    The paper presents the results of laboratory and pilot studies on the removal of chloramine from potable water using chlorination with a less-than-breakpoint dosage of chlorine, followed by treatment with catalytic activated carbon. The effect of the chlorine-to-nitrogen ratio, temperature, and carbon contact time were investigated to optimize conditions for chloramines removal and minimize the production of ammonia. Results demonstrated that prechlorination of water, followed by treatment with catalytic activated carbon, can degrade monochloramine to nitrogen gas as a main product. For all chlorine-to-ammonia ratios studied, the observed rates of monochloramine removal were higher at a temperature of 20 degrees C than they were at 5 degrees C. Generation of ammonia was slightly higher at the lower temperature. However, at both temperatures, practically all monochloramine was destroyed, and only insignificant amounts of ammonia were formed when a chlorine-to-ammonia ratio of 7:1 was applied. The described method is simple and cost-effective, because it eliminates the requirement of removal of ammonia, typically formed during the treatment of chloramines with activated carbon.

  14. Relief of autoinhibition by conformational switch explains enzyme activation by a catalytically dead paralog

    PubMed Central

    Volkov, Oleg A; Kinch, Lisa; Ariagno, Carson; Deng, Xiaoyi; Zhong, Shihua; Grishin, Nick; Tomchick, Diana R; Chen, Zhe; Phillips, Margaret A

    2016-01-01

    Catalytically inactive enzyme paralogs occur in many genomes. Some regulate their active counterparts but the structural principles of this regulation remain largely unknown. We report X-ray structures of Trypanosoma brucei S-adenosylmethionine decarboxylase alone and in functional complex with its catalytically dead paralogous partner, prozyme. We show monomeric TbAdoMetDC is inactive because of autoinhibition by its N-terminal sequence. Heterodimerization with prozyme displaces this sequence from the active site through a complex mechanism involving a cis-to-trans proline isomerization, reorganization of a β-sheet, and insertion of the N-terminal α-helix into the heterodimer interface, leading to enzyme activation. We propose that the evolution of this intricate regulatory mechanism was facilitated by the acquisition of the dimerization domain, a single step that can in principle account for the divergence of regulatory schemes in the AdoMetDC enzyme family. These studies elucidate an allosteric mechanism in an enzyme and a plausible scheme by which such complex cooperativity evolved. DOI: http://dx.doi.org/10.7554/eLife.20198.001 PMID:27977001

  15. Synthesis, characterization, and catalytic activity of type 2 crystalline titanates prepared with supercritical drying

    NASA Astrophysics Data System (ADS)

    Al-Adwani, Hamad A. H.

    Supercritically dried silico-alumino-titanate (Si-Al-Ti) mixed oxides (T2CT) were successfully synthesized by a sol-gel method with hydrothermal synthesis temperatures less than 200°C and autogenic pressure. High-surface-area T2CT aerogels with meso- to macroporosity were obtained. All solid products, after calcination at 450°C, are semicrystalline. In addition, successful scale-up of T2CT synthesis in a one-gallon reactor yielding 500 g was achieved. Surface areas, pore volumes, and average pore diameters are greatly influenced by the drying method. Supercritical drying had no effect on the crystalline or molecular structure of the materials. The synthesized materials were characterized by means of nitrogen physisorption, X-ray diffraction (XRD), thermal analysis, and diffuse reflectance FTIR spectroscopy. The addition of different amounts of phosphorous and antimony affected neither the textural nor the structural aspects of T2CT. However, a decrease in surface area occurred. The catalytic activity of these materials was evaluated after being loaded with nickel and molybdenum by the incipient wetness method. Cyclohexene hydrogenation and thiophene hydrodesulfurization reactions are used in the catalytic activity study. The activities of some of the catalyst prepared in this study are in the same range as the commercial catalyst, Shell 324, but with lower metal loadings than the commercial catalysts. Thus, more efficient use of Mo and Ni was observed.

  16. Role of enzyme-substrate flexibility in catalytic activity: an evolutionary perspective.

    PubMed

    Demetrius, L

    1998-09-21

    Site-directed mutagenesis has proved an effective experimental technique to investigate catalytic mechanisms and to determine relations between enzyme structure and function. This article invokes an analytical model based on evolution by mutation and natural selection-Nature's analogue of site-directed mutagenesis-to derive a set of general rules relating enzyme structure and activity. The catalysts are described in terms of the structural parameters, rigidity and flexibility, and the functional variables, reaction rate and substrate specificity. The evolutionary model predicts the following structure-activity relations: (a) rigid enzyme-flexible substrate: large variation in reaction rates, broad substrate specificity; (b) rigid enzyme-rigid substrate: diffusion controlled rates, absolute specificity; (c) flexible enzyme-rigid substrate: intermediate reaction rates, group specificity; (d) flexible enzyme-flexible substrate: slow rates, absolute specificity. Spectroscopic methods and X-ray crystallography now yield important characteristics of enzyme-substrate complexes such as molecular flexibility. The evolutionary analysis we have exploited provides general principles for inferring catalytic activity from structural studies of enzyme-substrate complexes.

  17. Active site structure and catalytic mechanism of phosphodiesterase for degradation of intracellular second messengers

    NASA Astrophysics Data System (ADS)

    Zhan, Chang-Guo

    2002-03-01

    Phosphodiesterases are clinical targets for a variety of biological disorders, because this superfamily of enzymes regulate intracellular concentration of cyclic nucleotides that serve as the second messengers playing a critical role in a variety of physiological processes. Understanding structure and mechanism of a phosphodiesterase will provide a solid basis for rational design of the more efficient therapeutics. Although a three-dimensional X-ray crystal structure of the catalytic domain of human phosphodiesterase 4B2B was recently reported, it was uncertain whether a critical bridging ligand in the active site is a water molecule or a hydroxide ion. The identity of this bridging ligand has been determined by performing first-principles quantum chemical calculations on models of the active site. All the results obtained indicate that this critical bridging ligand in the active site of the reported X-ray crystal structure is a hydroxide ion, rather than a water molecule, expected to serve as the nucleophile to initialize the catalytic degradation of the intracellular second messengers.

  18. Relief of autoinhibition by conformational switch explains enzyme activation by a catalytically dead paralog

    SciTech Connect

    Volkov, Oleg A.; Kinch, Lisa; Ariagno, Carson; Deng, Xiaoyi; Zhong, Shihua; Grishin, Nick; Tomchick, Diana R.; Chen, Zhe; Phillips, Margaret A.

    2016-12-15

    Catalytically inactive enzyme paralogs occur in many genomes. Some regulate their active counterparts but the structural principles of this regulation remain largely unknown. We report X-ray structures ofTrypanosoma brucei S-adenosylmethionine decarboxylase alone and in functional complex with its catalytically dead paralogous partner, prozyme. We show monomericTbAdoMetDC is inactive because of autoinhibition by its N-terminal sequence. Heterodimerization with prozyme displaces this sequence from the active site through a complex mechanism involving acis-to-transproline isomerization, reorganization of a β-sheet, and insertion of the N-terminal α-helix into the heterodimer interface, leading to enzyme activation. We propose that the evolution of this intricate regulatory mechanism was facilitated by the acquisition of the dimerization domain, a single step that can in principle account for the divergence of regulatory schemes in the AdoMetDC enzyme family. These studies elucidate an allosteric mechanism in an enzyme and a plausible scheme by which such complex cooperativity evolved.

  19. 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.

  20. 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

  1. 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.

  2. Analysis of the effect of temperature and reaction time on yields, compositions and oil quality in catalytic and non-catalytic lignin solvolysis in a formic acid/water media using experimental design.

    PubMed

    Oregui Bengoechea, Mikel; Miletíc, Nemanja; Vogt, Mari H; Arias, Pedro L; Barth, Tanja

    2017-03-01

    The catalytic solvolysis of Norway spruce (Picea abies L.) lignin in a formic acid/water media was explored at different temperatures and reaction times (283-397°C and 21-700min, respectively). Non-catalyzed experiments were compared with the effect of three different type of bifunctional catalysts (Pd/Al2O3, Rh/Al2O3 and Ru/Al2O3) and a solid Lewis acid (γ-Al2O3). We demonstrated that surface response methodology (RSM) and principal component analysis (PCA) were an adequate tool to: (i) evaluate the effect of the catalysts, temperature and reaction time in the oil yield, oil quality (H/C and O/C ratios, and Mw) and composition of the oil, (ii) establish the differences and/or similarities between the three bifunctional catalyst and (iii) to determine the role of the noble metal and the alumina support in the reaction system. In addition, the most active catalysts, Ru/Al2O3, and the optimum reaction conditions were determined (i.e. 340°C and 6h).

  3. Enhanced catalytic activity in strained chemically exfoliated WS₂ nanosheets for hydrogen evolution.

    PubMed

    Voiry, Damien; Yamaguchi, Hisato; Li, Junwen; Silva, Rafael; Alves, Diego C B; Fujita, Takeshi; Chen, Mingwei; Asefa, Tewodros; Shenoy, Vivek B; Eda, Goki; Chhowalla, Manish

    2013-09-01

    Efficient evolution of hydrogen through electrocatalysis at low overpotentials holds tremendous promise for clean energy. Hydrogen evolution can be easily achieved by electrolysis at large potentials that can be lowered with expensive platinum-based catalysts. Replacement of Pt with inexpensive, earth-abundant electrocatalysts would be significantly beneficial for clean and efficient hydrogen evolution. To this end, promising results have been reported using 2H (trigonal prismatic) XS₂ (where X  =  Mo or W) nanoparticles with a high concentration of metallic edges. The key challenges for XS₂ are increasing the number and catalytic activity of active sites. Here we report monolayered nanosheets of chemically exfoliated WS₂ as efficient catalysts for hydrogen evolution with very low overpotentials. Analyses indicate that the enhanced electrocatalytic activity of WS₂ is associated with the high concentration of the strained metallic 1T (octahedral) phase in the as-exfoliated nanosheets. Our results suggest that chemically exfoliated WS₂ nanosheets are interesting catalysts for hydrogen evolution.

  4. 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.

  5. 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.

  6. Proteasome Activity Profiling Uncovers Alteration of Catalytic β2 and β5 Subunits of the Stress-Induced Proteasome during Salinity Stress in Tomato Roots

    PubMed Central

    Kovács, Judit; Poór, Péter; Kaschani, Farnusch; Chandrasekar, Balakumaran; Hong, Tram N.; Misas-Villamil, Johana C.; Xin, Bo T.; Kaiser, Markus; Overkleeft, Herman S.; Tari, Irma; van der Hoorn, Renier A. L.

    2017-01-01

    The stress proteasome in the animal kingdom facilitates faster conversion of oxidized proteins during stress conditions by incorporating different catalytic β subunits. Plants deal with similar kind of stresses and also carry multiple paralogous genes encoding for each of the three catalytic β subunits. Here, we investigated the existence of stress proteasomes upon abiotic stress (salt stress) in tomato roots. In contrast to Arabidopsis thaliana, tomato has a simplified proteasome gene set with single genes encoding each β subunit except for two genes encoding β2. Using proteasome activity profiling on tomato roots during salt stress, we discovered a transient modification of the catalytic subunits of the proteasome coinciding with a loss of cell viability. This stress-induced active proteasome disappears at later time points and coincides with the need to degrade oxidized proteins during salt stress. Subunit-selective proteasome probes and MS analysis of fluorescent 2D gels demonstrated that the detected stress-induced proteasome is not caused by an altered composition of subunits in active proteasomes, but involves an increased molecular weight of both labeled β2 and β5 subunits, and an additional acidic pI shift for labeled β5, whilst labeled β1 remains mostly unchanged. Treatment with phosphatase or glycosidases did not affect the migration pattern. This stress-induced proteasome may play an important role in PCD during abiotic stress. PMID:28217134

  7. Proteasome Activity Profiling Uncovers Alteration of Catalytic β2 and β5 Subunits of the Stress-Induced Proteasome during Salinity Stress in Tomato Roots.

    PubMed

    Kovács, Judit; Poór, Péter; Kaschani, Farnusch; Chandrasekar, Balakumaran; Hong, Tram N; Misas-Villamil, Johana C; Xin, Bo T; Kaiser, Markus; Overkleeft, Herman S; Tari, Irma; van der Hoorn, Renier A L

    2017-01-01

    The stress proteasome in the animal kingdom facilitates faster conversion of oxidized proteins during stress conditions by incorporating different catalytic β subunits. Plants deal with similar kind of stresses and also carry multiple paralogous genes encoding for each of the three catalytic β subunits. Here, we investigated the existence of stress proteasomes upon abiotic stress (salt stress) in tomato roots. In contrast to Arabidopsis thaliana, tomato has a simplified proteasome gene set with single genes encoding each β subunit except for two genes encoding β2. Using proteasome activity profiling on tomato roots during salt stress, we discovered a transient modification of the catalytic subunits of the proteasome coinciding with a loss of cell viability. This stress-induced active proteasome disappears at later time points and coincides with the need to degrade oxidized proteins during salt stress. Subunit-selective proteasome probes and MS analysis of fluorescent 2D gels demonstrated that the detected stress-induced proteasome is not caused by an altered composition of subunits in active proteasomes, but involves an increased molecular weight of both labeled β2 and β5 subunits, and an additional acidic pI shift for labeled β5, whilst labeled β1 remains mostly unchanged. Treatment with phosphatase or glycosidases did not affect the migration pattern. This stress-induced proteasome may play an important role in PCD during abiotic stress.

  8. 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.

  9. Facile, template-free synthesis of silver nanodendrites with high catalytic activity for the reduction of p-nitrophenol.

    PubMed

    Zhang, Wei; Tan, Fatang; Wang, Wei; Qiu, Xiaolin; Qiao, Xueliang; Chen, Jianguo

    2012-05-30

    Here we report a facile, surfactant-free and template-free synthesis process of highly uniform dendritic silver nanostructures with high catalytic activity for the reduction of p-nitrophenol. By controlling the concentration of AgNO(3) aqueous solution and the reaction time, various shapes of silver nanodendrites (SNDs) could be obtained easily. The effects of different parameters such as concentrations of the reagents and reaction time on the morphology and structure of as-prepared tree-like nanostructures have also been investigated by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Also, the X-ray photoelectron spectroscopy (XPS) has been used to identify the oxidation state of SNDs. In addition, the catalytic activity of the as-prepared SNDs samples at 200 mM AgNO(3) aqueous solution was evaluated by a redox reaction of p-nitrophenol in the presence of an excess amount of NaBH(4). It was found that the highly symmetrical SNDs with roughly 60-120 nm in stem and branch diameter and 3-12 μm in length obtained after 120 s reaction time do have higher catalytic activity than other SNDs prepared at different reaction time, several times stronger catalytic activity in the sodium borohydride reduction of p-nitrophenol to p-aminophenol, compared to some other silver nanoparticles reported in literature. The crystallinity provided by X-ray diffraction (XRD) analysis indicates that the improvement of the crystallinity is also very crucial for SNDs' catalytic activities. The SNDs are very promising catalytic candidates for the reduction of p-nitrophenol because of easily simple preparation route and high catalytic activity.

  10. 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

  11. Advances in catalytic production of bio-based polyester monomer 2,5-furandicarboxylic acid derived from lignocellulosic biomass.

    PubMed

    Zhang, Junhua; Li, Junke; Tang, Yanjun; Lin, Lu; Long, Minnan

    2015-10-05

    Recently, the production and utilization of 2,5-furandicarboxylic acid (FDCA) have become a hot research topic in catalyst field and polyester industry for its special chemical structure and a wide range of raw material source. FDCA is a potential replacement for the terephthalic acid monomer used in the production of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), which opens up a new pathway for obtaining biomass-based polyester to replace or partially replace petroleum based polyester. Here, we mainly reviewed the catalytic pathway for the synthesis of FDCA derived from lignocellulosic biomass or from the related downstream products, such as glucose, 5-hydroxymethylfurfural (HMF). Moreover, the utilization of oxidation catalysts, the reaction mechanism, the existing limitations and unsolved challenges were also elaborated in detail. Therefore, we hope this mini review provides a helpful overview and insight to readers in this exciting research area.

  12. 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.

  13. Generation 9 polyamidoamine dendrimer encapsulated platinum nanoparticle mimics catalase size, shape, and catalytic activity.

    PubMed

    Wang, Xinyu; Zhang, Yincong; Li, Tianfu; Tian, Wende; Zhang, Qiang; Cheng, Yiyun

    2013-04-30

    Poly(amidoamine) (PAMAM) encapsulated platinum nanoparticles were synthesized and used as catalase mimics. Acetylated generation 9 (Ac-G9) PAMAM dendrimer with a molecular size around 10 nm was used as a template to synthesize platinum nanoparticles. The feeding molar ratio of Pt(4+) and Ac-G9 is 2048, and the synthesized platinum nanoparticle (Ac-G9/Pt NP) has an average size of 3.3 nm. Ac-G9/Pt NP has a similar molecular size and globular shape with catalase (~11 nm). The catalytic activity of Ac-G9/Pt NP on the decomposition of H2O2 is approaching that of catalase at 37 °C. Ac-G9/Pt NP shows differential response to the changes of pH and temperature compared with catalase, which can be explained by different catalytic mechanisms of Ac-G9/Pt NP and catalase. Ac-G9/Pt NP also shows horseradish peroxidase activity and is able to scavenge free radicals such as di(phenyl)-(2,4,6-trinitrophenyl)iminoazanium (DPPH). Furthermore, Ac-G9/Pt NP shows excellent biocompatibility on different cell lines and can down-regulate H2O2-induced intracellular reactive oxygen species (ROS) in these cells. These results suggest that dendrimers are promising mimics of proteins with different sizes and Ac-G9/Pt NP can be used as an alternative candidate of catalase to decrease oxidation stress in cells.

  14. [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.

  15. 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.

  16. Emergence of a catalytic tetrad during evolution of a highly active artificial aldolase

    NASA Astrophysics Data System (ADS)

    Obexer, Richard; Godina, Alexei; Garrabou, Xavier; Mittl, Peer R. E.; Baker, David; Griffiths, Andrew D.; Hilvert, Donald

    2017-01-01

    Designing catalysts that achieve the rates and selectivities of natural enzymes is a long-standing goal in protein chemistry. Here, we show that an ultrahigh-throughput droplet-based microfluidic screening platform can be used to improve a previously optimized artificial aldolase by an additional factor of 30 to give a >109 rate enhancement that rivals the efficiency of class I aldolases. The resulting enzyme catalyses a reversible aldol reaction with high stereoselectivity and tolerates a broad range of substrates. Biochemical and structural studies show that catalysis depends on a Lys-Tyr-Asn-Tyr tetrad that emerged adjacent to a computationally designed hydrophobic pocket during directed evolution. This constellation of residues is poised to activate the substrate by Schiff base formation, promote mechanistically important proton transfers and stabilize multiple transition states along a complex reaction coordinate. The emergence of such a sophisticated catalytic centre shows that there is nothing magical about the catalytic activities or mechanisms of naturally occurring enzymes, or the evolutionary process that gave rise to them.

  17. Effect of the dispersants on Pd species and catalytic activity of supported palladium catalyst

    NASA Astrophysics Data System (ADS)

    Hu, Yue; Yang, Xiaojun; Cao, Shuo; Zhou, Jie; Wu, Yuanxin; Han, Jinyu; Yan, Zhiguo; Zheng, Mingming

    2017-04-01

    A series of supported palladium catalysts has been prepared through the precipitation method and the reduction method, using polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) as dispersants. The effects of the dispersants on the properties of catalysts were evaluated and the catalytic performance of the new materials was investigated for the oxidative carbonylation of phenol to diphenyl carbonate (DPC). The catalysts as prepared were also characterized by the X-ray diffraction (XRD), transmission electron microscope (TEM), Brunner-Emmet-Teller (BET) measurements and X-ray photoelectron spectroscopy (XPS) techniques. The results show that the addition of the dispersants had no effect on the crystal phase of the catalysts. However, the dispersion of Pd particles was improved when the dispersants were used. Moreover, the particle sizes of Pd nanoparticles modified by PVA were smaller than those modified by PVP. The catalysts prepared using the dispersants gave better yields of DPC than the catalysts prepared without the dispersants. The highest yield of DPC was 17.9% with the PVA-Red catalyst. The characterization results for the used catalysts showed that the Pd species in the PVA-Red catalyst remained mostly divalent and the lattice oxygen species were consumed during the reaction, which could lead to the higher catalytic activity of the PVA-Red catalyst. The experimental results confirm that PVA effectively inhibited the sintering and reduction of active Pd species in the oxidative carbonylation of phenol.

  18. 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.

  19. Imparting Catalytic Activity to a Covalent Organic Framework Material by Nanoparticle Encapsulation.

    PubMed

    Shi, Xiaofei; Yao, Youjin; Xu, Yulong; Liu, Kun; Zhu, Guangshan; Chi, Lifeng; Lu, Guang

    2017-03-01

    Integrating covalent organic frameworks (COFs) with other functional materials is a useful route to enhancing their performances and extending their applications. We report herein a simple encapsulation method for incorporating catalytically active Au nanoparticles with different sizes, shapes, and contents in a two-dimensional (2D) COF material constructed by condensing 1,3,5-tris(4-aminophenyl)benzene (TAPB) with 2,5-dimethoxyterephthaldehyde (DMTP). The encapsulation is assisted by the surface functionalization of Au nanoparticles with polyvinylpyrrolidone (PVP) and follows a mechanism based on the adsorption of nanoparticles onto surfaces of the initially formed polymeric precursor of COF. The incorporation of nanoparticles does not alter obviously the crystallinity, thermal stability, and pore structures of the framework matrices. The obtained COF composites with embedded but accessible Au nanoparticles possess large surface areas and highly open mesopores and display recyclable catalytic performance for reduction of 4-nitrophenol, which cannot be catalyzed by the pure COF material, with activities relevant to contents and geometric structures of the incorporated nanoparticles.

  20. The AMP-activated protein kinase α2 catalytic subunit controls whole-body insulin sensitivity

    PubMed Central

    Viollet, Benoit; Andreelli, Fabrizio; Jørgensen, Sebastian B.; Perrin, Christophe; Geloen, Alain; Flamez, Daisy; Mu, James; Lenzner, Claudia; Baud, Olivier; Bennoun, Myriam; Gomas, Emmanuel; Nicolas, Gaël; Wojtaszewski, Jørgen F.P.; Kahn, Axel; Carling, David; Schuit, Frans C.; Birnbaum, Morris J.; Richter, Erik A.; Burcelin, Rémy; Vaulont, Sophie

    2003-01-01

    AMP-activated protein kinase (AMPK) is viewed as a fuel sensor for glucose and lipid metabolism. To better understand the physiological role of AMPK, we generated a knockout mouse model in which the AMPKα2 catalytic subunit gene was inactivated. AMPKα2–/– mice presented high glucose levels in the fed period and during an oral glucose challenge associated with low insulin plasma levels. However, in isolated AMPKα2–/– pancreatic islets, glucose- and L-arginine–stimulated insulin secretion were not affected. AMPKα2–/– mice have reduced insulin-stimulated whole-body glucose utilization and muscle glycogen synthesis rates assessed in vivo by the hyperinsulinemic euglycemic clamp technique. Surprisingly, both parameters were not altered in mice expressing a dominant-negative mutant of AMPK in skeletal muscle. Furthermore, glucose transport was normal in incubated isolated AMPKα2–/– muscles. These data indicate that AMPKα2 in tissues other than skeletal muscles regulates insulin action. Concordantly, we found an increased daily urinary catecholamine excretion in AMPKα2–/– mice, suggesting altered function of the autonomic nervous system that could explain both the impaired insulin secretion and insulin sensitivity observed in vivo. Therefore, extramuscular AMPKα2 catalytic subunit is important for whole-body insulin action in vivo, probably through modulation of sympathetic nervous activity. PMID:12511592

  1. The AMP-activated protein kinase alpha2 catalytic subunit controls whole-body insulin sensitivity.

    PubMed

    Viollet, Benoit; Andreelli, Fabrizio; Jørgensen, Sebastian B; Perrin, Christophe; Geloen, Alain; Flamez, Daisy; Mu, James; Lenzner, Claudia; Baud, Olivier; Bennoun, Myriam; Gomas, Emmanuel; Nicolas, Gaël; Wojtaszewski, Jørgen F P; Kahn, Axel; Carling, David; Schuit, Frans C; Birnbaum, Morris J; Richter, Erik A; Burcelin, Rémy; Vaulont, Sophie

    2003-01-01

    AMP-activated protein kinase (AMPK) is viewed as a fuel sensor for glucose and lipid metabolism. To better understand the physiological role of AMPK, we generated a knockout mouse model in which the AMPKalpha2 catalytic subunit gene was inactivated. AMPKalpha2(-/-) mice presented high glucose levels in the fed period and during an oral glucose challenge associated with low insulin plasma levels. However, in isolated AMPKalpha2(-/-) pancreatic islets, glucose- and L-arginine-stimulated insulin secretion were not affected. AMPKalpha2(-/-) mice have reduced insulin-stimulated whole-body glucose utilization and muscle glycogen synthesis rates assessed in vivo by the hyperinsulinemic euglycemic clamp technique. Surprisingly, both parameters were not altered in mice expressing a dominant-negative mutant of AMPK in skeletal muscle. Furthermore, glucose transport was normal in incubated isolated AMPKalpha2(-/-) muscles. These data indicate that AMPKalpha2 in tissues other than skeletal muscles regulates insulin action. Concordantly, we found an increased daily urinary catecholamine excretion in AMPKalpha2(-/-) mice, suggesting altered function of the autonomic nervous system that could explain both the impaired insulin secretion and insulin sensitivity observed in vivo. Therefore, extramuscular AMPKalpha2 catalytic subunit is important for whole-body insulin action in vivo, probably through modulation of sympathetic nervous activity.

  2. Promoting immobilization and catalytic activity of horseradish peroxidase on mesoporous silica through template micelles.

    PubMed

    Wan, Mi Mi; Lin, Wei Gang; Gao, Ling; Gu, Hui Cheng; Zhu, Jian Hua

    2012-07-01

    New concept on the promotion of immobilization and catalytic activity of enzyme on mesoporous silica through template micelles is proposed and realized in this paper. Proper P123 templates are controllable retained in the as-synthesized SBA-15, not only to anchor the horseradish peroxidase (HRP) guest, but also to establish the crowding-like microenvironment around the enzyme. The influence of retaining templates on the pore structure of SBA-15, immobilization, and catalytic activity of HRP is studied, and the possible process of template removal is proposed. Ethanol refluxing of 6 h is conformable to prepare the optimal mesoporous support characterized with the retained templates of about 8%. With the assistance of retained templates in SBA-15, up to 49 mg g(-1) of HRP can be immobilized, 100% more than that on calcined SBA-15. Furthermore, the thermal stability, the resistance of pH variation and denaturing agent urea, and the recycle usage of HRP immobilized are obviously elevated, paving a novel and low-cost route to develop enzyme catalysts.

  3. 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

  4. 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

    2015-03-09

    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

    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.

  6. 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.

  7. 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.

  8. The photo-catalytic activities of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) microparticles

    NASA Astrophysics Data System (ADS)

    Zhang, Fan; Shi, Yuanji; Zhao, Zongshan; Song, Weijie; Cheng, Yang

    2014-02-01

    For the good performance of apatite-based materials in the removal of dyes and their environment-friendly advantage, five kinds of apatite microparticles of MP (M = Ba, Ca, Cu, Sr, Ag; P = PO43-, HPO42-) were synthesized by a simple precipitation method and their photo-catalytic properties were invested. Better performance in the decolorization of methyl orange (MO) under the assistance of H2O2 than that of TiO2 were obtained for all the MPs. The photo-catalytic activity was mainly affected by surface area, energy band, impurity, crystallinity and crystal structure. The DFT calculation results demonstrated that the 2p of O and 3p of P in PO43- played the main role in the photo-catalytic process. This work would be helpful to design and synthesize low cost apatite materials with good photo-catalytic performance.

  9. 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.

  10. Catalytic hydrodechlorination of monochloroacetic acid in wastewater using Ni-Fe bimetal prepared by ball milling.

    PubMed

    Zhu, Hong; Xu, Fuyuan; Zhao, Jianzhuang; Jia, Linfang; Wu, Kunming

    2015-09-01

    Monochloroacetic acid (MCA) is a chemically stable and biologically toxic pollutant. It is often generated during the production of the pesticide dimethoate. Conventional wastewater treatment processes have difficulty degrading it. In this work, the dechlorination effects of Ni-Fe bimetal prepared using ball milling (BM) technology for the high concentrations of MCA in wastewater were examined. The MCA in aqueous solution was found to be degraded efficiently by the Ni-Fe bimetal. However, S-(methoxycarbonyl) methyl O, O-dimethyl phosphorodithioate (SMOPD) in wastewater, a by-product of the dimethoate production process, significantly inhibited the reductive dechlorination activity of Ni-Fe bimetal. Increasing the reaction temperature in the MCA wastewater enhanced the reduction activity of the Ni-Fe bimetal effectively. Oxygen was found to be unfavorable to dechlorination. Sealing the reaction to prevent oxidation was found to render the degradation process more efficient. The process retained over 88% efficiency after 10 treatment cycles with 50 g/L of Ni-Fe bimetal under field conditions.

  11. The CDC2-related kinase PITALRE is the catalytic subunit of active multimeric protein complexes.

    PubMed Central

    Garriga, J; Mayol, X; Graña, X

    1996-01-01

    PITALRE is a human protein kinase identified by means of its partial sequence identity to the cell division cycle regulatory kinase CDC2. Immunopurified PITALRE protein complexes exhibit an in vitro kinase activity that phosphorylates the retinoblastoma protein, suggesting that PITALRE catalyses this phosphorylation reaction. However, the presence of other kinases in the immunopurified complex could not be ruled out. In the present work, an inactive mutant of the PITALRE kinase has been used to demonstrate that PITALRE is the catalytic subunit responsible for the PITALRE-complex-associated kinase activity, Ectopic overexpression of PITALRE did not increase the total PITALRE kinase activity in the cell, suggesting that PITALRE is regulated by limiting cellular factor(s). Characterization of the PITALRE-containing protein complexes indicated that most of the cellular PITALRE protein exists as a subunit in at least two different active multimeric complexes. Although monomeric PITALRE is also active in vitro, PITALRE present in multimeric complexes exhibits several-fold higher activity than monomeric PITALRE. In addition, overexpression of PITALRE demonstrated the existence of two new associated proteins of approx. 48 and 98 kDa. Altogether these results suggest that, in contrast to the situation with cyclin-dependent kinases, monomeric PITALRE is active, and that association with other proteins modulates its activity and/or its ability to recognize substrates in vivo. PMID:8870681

  12. E2 superfamily of ubiquitin-conjugating enzymes: constitutively active or activated through phosphorylation in the catalytic cleft

    PubMed Central

    Valimberti, Ilaria; Tiberti, Matteo; Lambrughi, Matteo; Sarcevic, Boris; Papaleo, Elena

    2015-01-01

    Protein phosphorylation is a modification that offers a dynamic and reversible mechanism to regulate the majority of cellular processes. Numerous diseases are associated with aberrant regulation of phosphorylation-induced switches. Phosphorylation is emerging as a mechanism to modulate ubiquitination by regulating key enzymes in this pathway. The molecular mechanisms underpinning how phosphorylation regulates ubiquitinating enzymes, however, are elusive. Here, we show the high conservation of a functional site in E2 ubiquitin-conjugating enzymes. In catalytically active E2s, this site contains aspartate or a phosphorylatable serine and we refer to it as the conserved E2 serine/aspartate (CES/D) site. Molecular simulations of substrate-bound and -unbound forms of wild type, mutant and phosphorylated E2s, provide atomistic insight into the role of the CES/D residue for optimal E2 activity. Both the size and charge of the side group at the site play a central role in aligning the substrate lysine toward E2 catalytic cysteine to control ubiquitination efficiency. The CES/D site contributes to the fingerprint of the E2 superfamily. We propose that E2 enzymes can be divided into constitutively active or regulated families. E2s characterized by an aspartate at the CES/D site signify constitutively active E2s, whereas those containing a serine can be regulated by phosphorylation. PMID:26463729

  13. Synthesis of zinc oxide nanostructures catalytically active in the optical range without irradiation

    NASA Astrophysics Data System (ADS)

    Kasumov, M. M.

    2012-09-01

    A technique for synthesizing catalytically active zinc oxide-based nanostructures is described. The synthesis product represents a blue-gray powder. When it is introduced into a water solution of methyl orange the latter bleaches out both under daylight and in the dark. The activity of the material is measured by the Kubelka-Munk formula in the wavelength range 0.3-1.8 μm. As follows from X-ray phase analysis data, the synthesized material is a composite consisting of hexagonal structures with the parameters ZnO [ a: 3.2491, c: 5.2046] and Zn [ a: 2.6639, c: 4.9397]. A mechanism underlying the formation of a ZnO-Zn nanocomposite is suggested.

  14. Stellated Ag-Pt bimetallic nanoparticles: An effective platform for catalytic activity tuning

    PubMed Central

    Liu, Hui; Ye, Feng; Yao, Qiaofeng; Cao, Hongbin; Xie, Jianping; Lee, Jim Yang; Yang, Jun

    2014-01-01

    The usefulness of Pt-based nanomaterials for catalysis can be greatly enhanced by coupling morphology engineering to the strategic presence of a second or even third metal. Here we demonstrate the design and preparation of stellated Ag-Pt bimetallic nanoparticles where significant activity difference between the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR) may be realized by relegating Ag to the core or by hollowing out the core. In particular the stellated Pt surface, with an abundance of steps, edges, corner atoms, and {111} facets, is highly effective for the ORR but is ineffective for MOR. MOR activity is only observed in the presence of a Ag core through electronic coupling to the stellated Pt shell. The bimetallic Ag-Pt stellates therefore demonstrate the feasibility of tuning a Pt surface for two very different structure sensitive catalytic reactions. Stellated bimetallics may therefore be an effective platform for highly tunable catalyst designs. PMID:24495979

  15. Synergy among manganese, nitrogen and carbon to improve the catalytic activity for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Kang, Jian; Wang, Hui; Ji, Shan; Key, Julian; Wang, Rongfang

    2014-04-01

    A highly active electrocatalyst for oxygen reduction reaction, manganese modified glycine derivative-carbon (Mn-CNx), is synthesized by a two-step carbonizing process. X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy are used to characterize structure and morphology of the catalysts. Electrochemical tests show that Mn-CNx has higher catalytic activity for oxygen reduction reaction than CNx derived glycine and Mn modified Vulcan carbon. Moreover, the half-wave potential of Mn-CNx is only 12 mV lower than that of commercial Pt/C. Mn-CNx also has excellent durability to methanol crossover in alkaline solution, and thus provides a promising low cost, non-precious metal cathode catalyst for fuel cells.

  16. Strong and coverage-independent promotion of catalytic activity of a noble metal by subsurface vanadium

    NASA Astrophysics Data System (ADS)

    Reichl, Wolfgang; Hayek, Konrad

    2003-07-01

    While common bimetallic surfaces have a variable composition, the stable subsurface alloys of V/Rh and V/Pd are characterised by a purely noble metal-terminated surface and the second metal positioned in near-surface layers. The uniform composition of the topmost surface layer excludes conventional ensemble effects in catalysis, and the activity of the surface can be controlled by the metal loading and by the temperature of annealing. For example, the activity of a polycrystalline Rh surface in CO hydrogenation is significantly increased by promotion with subsurface vanadium. The modification of the subsurface layer with a different metal must be considered a promising approach to improve the catalytic properties of a metal surface.

  17. Inhibition effect of graphene oxide on the catalytic activity of acetylcholinesterase enzyme.

    PubMed

    Wang, Yong; Gu, Yao; Ni, Yongnian; Kokot, Serge

    2015-11-01

    Variations in the enzyme activity of acetylcholinesterase (AChE) in the presence of the nano-material, graphene oxide (GO), were investigated with the use of molecular spectroscopy UV-visible and fluorescence methods. From these studies, important kinetic parameters of the enzyme were extracted; these were the maximum reaction rate, Vm , and the Michaelis constant, Km . A comparison of these parameters indicated that GO inhibited the catalytic activity of the AChE because of the presence of the AChE-GO complex. The formation of this complex was confirmed with the use of fluorescence data, which was resolved with the use of the MCR-ALS chemometrics method. Furthermore, it was found that the resonance light-scattering (RLS) intensity of AChE changed in the presence of GO. On this basis, it was demonstrated that the relationship between AChE and GO was linear and such models were used for quantitative analyses of GO.

  18. Metabolic conditions determining the composition and catalytic activity of cytochrome P-450 monooxygenases in Candida tropicalis.

    PubMed Central

    Sanglard, D; Käppeli, O; Fiechter, A

    1984-01-01

    In the microsomal fraction of Candida tropicalis cells, two distinct monooxygenases were detected, depending on the growth conditions. The distinction of the two monooxygenases was evident from: (i) the absorption maxima in the reduced CO difference spectra of the terminal oxidases (cytochromes P-450 and P-448); (ii) the contents of the monooxygenase components (cytochromes P-450/P-448, NADPH-cytochrome c (P-450) reductase, and cytochrome b5) and (iii) the catalytic activity of the complete system (aliphatic hydroxylation and N-demethylation activity). The occurrence of the respective monooxygenases could be related to the carbon source (n-alkanes or glucose). Oxygen limitation led to a significant increase of cytochrome P-450/P-448 content, independent of the carbon source utilized by the cells. An improved method for the isolation of microsomes enabled us to demonstrate the presence of cytochrome P-448 in glucose-grown cells. PMID:6690424

  19. Assessing the Catalytic Activity of Transglutaminases in the Context of Autophagic Responses.

    PubMed

    D'Eletto, M; Farrace, M G; Piacentini, M; Rossin, F

    2017-01-01

    The human transglutaminases (TGases) are a widely distributed and peculiar group of enzymes that catalyze the posttranslational modification of proteins by the formation of isopeptide bonds. Tissue or type 2 transglutaminase (TG2) represents the most ubiquitous isoform belonging to TGases family. The vast array of biochemical functions catalyzed by TG2 distinguishes it from the other members of the TGase family. In the presence of high calcium levels TG2 catalyzes a vast array of protein posttranslational modifications, including protein-protein cross-linking, incorporation of primary amines into proteins, as well as glutamine deamination. In the last few years, it has become evident that TG2 is involved in the final maturation of autolysosomes. The TG2 regulation of autophagy occurs by its transamidating activity and its inhibition results in the intracellular increase of ubiquitinated protein aggregates. In this chapter, we describe the methods used in our laboratories to assess the catalytic activity of TG2 in the autophagic process.

  20. Catalytic catechol oxidation by copper complexes: development of a structure-activity relationship.

    PubMed

    Ording-Wenker, Erica C M; Siegler, Maxime A; Lutz, Martin; Bouwman, Elisabeth

    2015-07-21

    A large library of Cu(II) complexes with mononucleating and dinucleating ligands was synthesized to investigate their potential as catalysts for the catalytic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC). X-ray structure determination for a number of these complexes revealed relatively large Cu···Cu distances and the formation of polymeric species. Comparison of the 3,5-DTBC oxidation rates showed that ligands that stabilize the biomimetic dinuclear Cu(II) μ-thiolate complex also result in copper compounds that are much more active in the oxidation of 3,5-DTBC. This oxidation activity is however inhibited by the presence of chloride ions. The highest kcat that was observed was 6900 h(-1), which is one of the highest turnover frequencies reported so far for catechol oxidation in CH3CN.

  1. Synthesis of 1-dodecanethiol-capped Ag nanoparticles and their high catalytic activity

    NASA Astrophysics Data System (ADS)

    Zhang, Danhui; Yang, Youbo

    2017-01-01

    Silver nanoparticles, which were produced by the borohydride reduction of silver nitrate, were stabilized by means of 1-dodecanethiol providing sulfur atom in two-phase system involving water and organic solvent (such as toluene, chloroform and hexane). Different organic solvent played a major role in the particle size of silver nanoparticles. These silver nanoparticles synthesized in the three different organic solvent were characterized by X-ray Diffraction, transmission electron microscopy and ultraviolet-visible absorption spectroscopy. The results indicate that the particles size of silver nanoparticles formed in three organic solvents was different. Furthermore, 1-dodecanethiol-capped silver nanoparticles were found to serve as effective catalysts to activate the reduction of 4-nitrophenol (4NP) in the presence of NaBH4, where the size of silver nanoparticles played the determining role in catalytic activity.

  2. The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction.

    PubMed

    Kato, Shunsuke; Matam, Santhosh Kumar; Kerger, Philipp; Bernard, Laetitia; Battaglia, Corsin; Vogel, Dirk; Rohwerder, Michael; Züttel, Andreas

    2016-05-10

    Atomic hydrogen on the surface of a metal with high hydrogen solubility is of particular interest for the hydrogenation of carbon dioxide. In a mixture of hydrogen and carbon dioxide, methane was markedly formed on the metal hydride ZrCoHx in the course of the hydrogen desorption and not on the pristine intermetallic. The surface analysis was performed by means of time-of-flight secondary ion mass spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy, for the in situ analysis. The aim was to elucidate the origin of the catalytic activity of the metal hydride. Since at the initial stage the dissociation of impinging hydrogen molecules is hindered by a high activation barrier of the oxidised surface, the atomic hydrogen flux from the metal hydride is crucial for the reduction of carbon dioxide and surface oxides at interfacial sites.

  3. Catalytic activity and mechanistic approach of NO reduction by CO over M0.05Co2.95O4 (M = Rh, Pd & Ru) spinel system

    NASA Astrophysics Data System (ADS)

    Salker, A. V.; Desai, M. S. Fal

    2016-12-01

    Pd, Rh and Ru doped cobalt oxide spinels have been prepared by citric acid assisted sol-gel method to yield nano-catalysts. Compositions have been characterized by XRD, FTIR, TG/DTA, BET, SEM, TEM, TPD and XPS techniques. Simultaneous catalytic detoxification of nitric oxide and carbon monoxide is investigated over the doped and pristine catalysts. Metal doping is found to enhance the activity of the catalysts due to their better adsorption capacity. Moisture and oxygen tolerance is investigated for Rh and Pd substituted catalysts. A probable reaction mechanism on the catalyst surface has been proposed.

  4. 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...

  5. PiZ Mouse Liver Accumulates Polyubiquitin Conjugates That Associate with Catalytically Active 26S Proteasomes

    PubMed Central

    Haddock, Christopher J.; Bl