Betaine protects urea-induced denaturation of myosin subfragment-1.

PubMed

Ortiz-Costa, Susana; Sorenson, Martha M; Sola-Penna, Mauro

2008-07-01

We have demonstrated previously that urea inhibits the activity and alters the tertiary structure of skeletal muscle myosin in a biphasic manner. This was attributed to differential effects on its globular and filamentous portion. The inhibition of catalytic activity was counteracted by methylamines. With the aim of comprehending the effects of urea on the catalytic (globular) portion of myosin, this study examines the effects of urea and the countereffects of betaine on the catalytic activity and structure of myosin subfragment-1. It is shown that urea inactivates subfragment-1 in parallel with its ability to induce exposure of the enzyme hydrophobic domains, as assessed using intrinsic and extrinsic fluorescence. Both effects are counteracted by betaine, which alone does not significantly affect subfragment-1. Urea also enhances the accessibility of thiol groups, promotes aggregation and decreases the alpha-helix content of S1, effects that are also counteracted by betaine. We conclude that urea-induced inactivation of the enzyme is caused by partial unfolding of the myosin catalytic domain.

Inactivation of ceramide synthase 2 catalytic activity in mice affects transcription of genes involved in lipid metabolism and cell division.

PubMed

Bickert, Andreas; Kern, Paul; van Uelft, Martina; Herresthal, Stefanie; Ulas, Thomas; Gutbrod, Katharina; Breiden, Bernadette; Degen, Joachim; Sandhoff, Konrad; Schultze, Joachim L; Dörmann, Peter; Hartmann, Dieter; Bauer, Reinhard; Willecke, Klaus

2018-07-01

The replacement of two consecutive histidine residues by alanine residues in the catalytic center of ceramide synthase 2 in a new transgenic mouse mutant (CerS2 H/A) leads to inactivation of catalytic activity and reduces protein level to 60% of the WT level. We show here by qRT-PCR and transcriptome analyses that several transcripts of genes involved in lipid metabolism and cell division are differentially regulated in livers of CerS2 H/A mice. Thus, very long chain ceramides produced by CerS2 are required for transcriptional regulation of target genes. The hepatocellular carcinomata previously described in old CerS2 KO mice were already present in 8-week-old CerS2 H/A animals and thus are caused by the loss of CerS2 catalytic activity already during early life. Copyright © 2018 Elsevier B.V. All rights reserved.

Evaluating differences in the active-site electronics of supported Au nanoparticle catalysts using Hammett and DFT studies

NASA Astrophysics Data System (ADS)

Kumar, Gaurav; Tibbitts, Luke; Newell, Jaclyn; Panthi, Basu; Mukhopadhyay, Ahana; Rioux, Robert M.; Pursell, Christopher J.; Janik, Michael; Chandler, Bert D.

2018-03-01

Supported metal catalysts, which are composed of metal nanoparticles dispersed on metal oxides or other high-surface-area materials, are ubiquitous in industrially catalysed reactions. Identifying and characterizing the catalytic active sites on these materials still remains a substantial challenge, even though it is required to guide rational design of practical heterogeneous catalysts. Metal-support interactions have an enormous impact on the chemistry of the catalytic active site and can determine the optimum support for a reaction; however, few direct probes of these interactions are available. Here we show how benzyl alcohol oxidation Hammett studies can be used to characterize differences in the catalytic activity of Au nanoparticles hosted on various metal-oxide supports. We combine reactivity analysis with density functional theory calculations to demonstrate that the slope of experimental Hammett plots is affected by electron donation from the underlying oxide support to the Au particles.

The Catalytic Function of Enzymes.

ERIC Educational Resources Information Center

Splittgerber, Allan G.

1985-01-01

Discusses: structure of the enzyme molecule; active site; reaction mechanism; transition state; factors affecting enzyme reaction rates, concentration of enzyme; concentration of substrate; product concentration; temperature effects and pH effects; factors causing a lowering of activation energy; proximity and orientation effects; substrate strain…

Highly Dispersed Nickel-Containing Mesoporous Silica with Superior Stability in Carbon Dioxide Reforming of Methane: The Effect of Anchoring

PubMed Central

Cai, Wenjia; Ye, Lin; Zhang, Li; Ren, Yuanhang; Yue, Bin; Chen, Xueying; He, Heyong

2014-01-01

A series of nickel-containing mesoporous silica samples (Ni-SiO2) with different nickel content (3.1%–13.2%) were synthesized by the evaporation-induced self-assembly method. Their catalytic activity was tested in carbon dioxide reforming of methane. The characterization results revealed that the catalysts, e.g., 6.7%Ni-SiO2, with highly dispersed small nickel particles, exhibited excellent catalytic activity and long-term stability. The metallic nickel particle size was significantly affected by the metal anchoring effect between metallic nickel particles and unreduced nickel ions in the silica matrix. A strong anchoring effect was suggested to account for the remaining of small Ni particle size and the improved catalytic performance. PMID:28788570

Effect of pretreatment on pd/Al2O3 catalyst for catalytic oxidation of o-xylene at low temperature.

PubMed

Huang, Shaoyong; Zhang, Changbin; He, Hong

2013-06-01

The effect of pretreatment on Pd/Al2O3 catalysts for the catalytic oxidation of o-xylene at low temperature was studied by changing the pretreatment and testing conditions. The fresh and pretreated Pd/Al2O3 catalysts were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results showed that the pretreatment dramatically changed the Pd/PdO ratio and then significantly affected the Pd/Al2O3 activity; while the pretreatment had not much influence on Pd particle size. The Pd/Al2O3 pre-reduced at 300 degrees C/400 degrees C, which has fully reduced Pd species, showed the highest activity; while the fresh Pd/Al2O3, which has fully oxidized Pd species, presented the worst performance, indicating the Pd chemical state plays an important role in the catalytic activity for the o-xylene oxidation. It is concluded that metallic Pd is the active species on the Pd/Al2O3 catalyst for the catalytic oxidation of o-xylene at low temperature.

Changes in spectrochemical and catalytic properties of biopolymer anchored Cu(II) and Ni(II) catalysts by electron beam irradiation.

PubMed

Antony, R; Suja Pon Mini, P S; Theodore David Manickam, S; Sanjeev, Ganesh; Mitu, Liviu; Balakumar, S

2015-01-01

Chitosan (a biopolymer) anchored Cu(II) and Ni(II) Schiff base complexes, [M(OIAC)Cl2] (M: Cu/Ni and OIAC: ([2-oxo-1H-indol-3-ylidene]amino)chitosan) were electron beam irradiated by different doses (100 Gy, 1 kGy and 10 kGy). The electron beam has shown potential impact on biopolymer's support, in detail chain linking and chain scissoring, as evidenced by viscosity studies, FT-IR and X-ray diffraction spectroscopic techniques. Due to these structural changes, thermal properties of the complexes were found to be changed. The surface of these heterogeneous complexes was also effectually altered by electron beam. As a consequence, pores and holes were created as probed by SEM technique. The catalytic activity of both non-irradiated and irradiated complexes was investigated in the aerobic oxidation of cyclohexane using hydrogen peroxide oxidant. The catalytic ability of the complexes was enhanced significantly after irradiation as the result of surface changes. The reusability of the complexes was also greatly affected because of the structural variations in polymeric support. In terms of both better catalytic activity along with the reusability, 1 kGy is suggested as the best dose to attain adequate increase in catalytic activity and good reusability. Copyright © 2015 Elsevier B.V. All rights reserved.

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

Functional effects of single nucleotide polymorphisms in the coding region of human N-acetyltransferase 1

PubMed Central

Zhu, Yuanqi; Hein, David W.

2007-01-01

Genetic variants of human N-acetyltransferase 1 (NAT1) are associated with cancer and birth defects. N- and O-acetyltransferase catalytic activities, Michaelis-Menten kinetic constants (Km & Vmax), and steady state expression levels of NAT1-specific mRNA and protein were determined for the reference NAT1*4 and variant human NAT1 haplotypes possessing single nucleotide polymorphisms (SNPs) in the open reading frame. Although none of the SNPs caused a significant effect on steady state levels of NAT1-specific mRNA, C97T(R33stop), C190T(R64W), C559T (R187stop) and A752T(D251V) each reduced NAT1 protein level and/or N- and O-acetyltransferase catalytic activities to levels below detection. G560A(R187Q) substantially reduced NAT1 protein level and catalytic activities and increased substrate Km. The G445A(V149I), G459A(synonymous) and T640G(S214A) haplotype present in NAT1*11 significantly (p<0.05) increased NAT1 protein level and catalytic activity. Neither T21G(synonymous), T402C(synonymous), A613G(M205V), T777C(synonymous), G781A(E261K), or A787G(I263V) significantly affected Km, catalytic activity, mRNA or protein level. These results suggest heterogeneity among slow NAT1 acetylator phenotypes. PMID:17909564

Structure and Functional Characterization of Human Histidine Triad Nucleotide-Binding Protein 1 Mutations Associated with Inherited Axonal Neuropathy with Neuromyotonia.

PubMed

Shah, Rachit M; Maize, Kimberly M; West, Harrison T; Strom, Alexander M; Finzel, Barry C; Wagner, Carston R

2018-05-19

Inherited peripheral neuropathies are a group of neurodegenerative disorders that clinically affect 1 in 2500 individuals. Recently, genetic mutations in human histidine nucleotide-binding protein 1 (hHint1) have been strongly and most frequently associated with patients suffering from axonal neuropathy with neuromyotonia. However, the correlation between the impact of these mutations on the hHint1 structure, enzymatic activity and in vivo function has remained ambiguous. Here, we provide detailed biochemical characterization of a set of these hHint1 mutations. Our findings indicate that half of the mutations (R37P, G93D and W123*) resulted in a destabilization of the dimeric state and a significant decrease in catalytic activity and HINT1 inhibitor binding affinity. The H112N mutant was found to be dimeric, but devoid of catalytic activity, due to the loss of the catalytically essential histidine; nevertheless, it exhibited high affinity to AMP and a HINT1 inhibitor. In contrast to the active-site mutants, the catalytic activity and dimeric structure of the surface mutants, C84R and G89V, were found to be similar to the wild-type enzyme. Taken together, our results suggest that the pathophysiology of inherited axonal neuropathy with neuromyotonia can be induced by conversion of HINT1 from a homodimer to monomer, by modification of select surface residues or by a significant reduction of the enzyme's catalytic efficiency. Copyright © 2018. Published by Elsevier Ltd.

[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.

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.

A facile reflux procedure to increase active surface sites form highly active and durable supported palladium@platinum bimetallic nanodendrites

NASA Astrophysics Data System (ADS)

Wang, Qin; Li, Yingjun; Liu, Baocang; Xu, Guangran; Zhang, Geng; Zhao, Qi; Zhang, Jun

2015-11-01

A series of well-dispersed bimetallic Pd@Pt nanodendrites uniformly supported on XC-72 carbon black are fabricated by using different capping agents. These capping agents are essential for the branched morphology control. However, the surfactant adsorbed on the nanodendrites surface blocks the access of reactant molecules to the active surface sites, and the catalytic activities of these bimetallic nanodendrites are significantly restricted. Herein, a facile reflux procedure to effectively remove the capping agent molecules without significantly affecting their sizes is reported for activating supported nanocatalysts. More significantly, the structure and morphology of the nanodendrites can also be retained, enhancing the numbers of active surface sites, catalytic activity and stability toward methanol and ethanol electro-oxidation reactions. The as-obtained hot water reflux-treated Pd@Pt/C catalyst manifests superior catalytic activity and stability both in terms of surface and mass specific activities, as compared to the untreated catalysts and the commercial Pt/C and Pd/C catalysts. We anticipate that this effective and facile removal method has more general applicability to highly active nanocatalysts prepared with various surfactants, and should lead to improvements in environmental protection and energy production.

Effects of metal ions on the catalytic degradation of dicofol by cellulase.

PubMed

Zhai, Zihan; Yang, Ting; Zhang, Boya; Zhang, Jianbo

2015-07-01

A new technique whereby cellulase immobilized on aminated silica was applied to catalyze the degradation of dicofol, an organochlorine pesticide. In order to evaluate the performance of free and immobilized cellulase, experiments were carried out to measure the degradation efficiency. The Michaelis constant, Km, of the reaction catalyzed by immobilized cellulase was 9.16 mg/L, and the maximum reaction rate, Vmax, was 0.40 mg/L/min, while that of free cellulase was Km=8.18 mg/L, and Vmax=0.79 mg/L/min, respectively. The kinetic constants of catalytic degradation were calculated to estimate substrate affinity. Considering that metal ions may affect enzyme activity, the effects of different metal ions on the catalytic degradation efficiency were explored. The results showed that the substrate affinity decreased after immobilization. Monovalent metal ions had no effect on the reaction, while divalent metal ions had either positive or inhibitory effects, including activation by Mn2+, reversible competition with Cd2+, and irreversible inhibition by Pb2+. Ca2+ promoted the catalytic degradation of dicofol at low concentrations, but inhibited it at high concentrations. Compared with free cellulase, immobilized cellulase was affected less by metal ions. This work provided a basis for further studies on the co-occurrence of endocrine-disrupting chemicals and heavy metal ions in the environment. Copyright © 2015. Published by Elsevier B.V.

Post-translational generation of constitutively active cores from larger phosphatases in the malaria parasite, Plasmodium falciparum: implications for proteomics

PubMed Central

Kumar, Rajinder; Musiyenko, Alla; Oldenburg, Anja; Adams, Brian; Barik, Sailen

2004-01-01

Background Although the complete genome sequences of a large number of organisms have been determined, the exact proteomes need to be characterized. More specifically, the extent to which post-translational processes such as proteolysis affect the synthesized proteins has remained unappreciated. We examined this issue in selected protein phosphatases of the protease-rich malaria parasite, Plasmodium falciparum. Results P. falciparum encodes a number of Ser/Thr protein phosphatases (PP) whose catalytic subunits are composed of a catalytic core and accessory domains essential for regulation of the catalytic activity. Two examples of such regulatory domains are found in the Ca+2-regulated phosphatases, PP7 and PP2B (calcineurin). The EF-hand domains of PP7 and the calmodulin-binding domain of PP2B are essential for stimulation of the phosphatase activity by Ca+2. We present biochemical evidence that P. falciparum generates these full-length phosphatases as well as their catalytic cores, most likely as intermediates of a proteolytic degradation pathway. While the full-length phosphatases are activated by Ca+2, the processed cores are constitutively active and either less responsive or unresponsive to Ca+2. The processing is extremely rapid, specific, and occurs in vivo. Conclusions Post-translational cleavage efficiently degrades complex full-length phosphatases in P. falciparum. In the course of such degradation, enzymatically active catalytic cores are produced as relatively stable intermediates. The universality of such proteolysis in other phosphatases or other multi-domain proteins and its potential impact on the overall proteome of a cell merits further investigation. PMID:15230980

Clear microstructure-performance relationships in Mn-containing perovskite and hexaaluminate compounds prepared by activated reactive synthesis.

PubMed

Laassiri, Said; Bion, Nicolas; Duprez, Daniel; Royer, Sébastien; Alamdari, Houshang

2014-03-07

Microstructural properties of mixed oxides play essential roles in their oxygen mobility and consequently in their catalytic performances. Two families of mixed oxides (perovskite and hexaaluminate) with different microstructural features, such as crystal size and specific surface area, were prepared using the activated reactive synthesis (ARS) method. It was shown that ARS is a flexible route to synthesize both mixed oxides with nano-scale crystal size and high specific surface area. Redox properties and oxygen mobility were found to be strongly affected by the material microstructure. Catalytic activities of hexaaluminate and perovskite materials for methane oxidation were discussed in the light of structural, redox and oxygen mobility properties.

Graphene oxide for acid catalyzed-reactions: Effect of drying process

NASA Astrophysics Data System (ADS)

Gong, H. P.; Hua, W. M.; Yue, Y. H.; Gao, Z.

2017-03-01

Graphene oxides (GOs) were prepared by Hummers method through various drying processes, and characterized by XRD, SEM, FTIR, XPS and N2 adsorption. Their acidities were measured using potentiometric titration and acid-base titration. The catalytic properties were investigated in the alkylation of anisole with benzyl alcohol and transesterification of triacetin with methanol. GOs are active catalysts for both reaction, whose activity is greatly affected by their drying processes. Vacuum drying GO exhibits the best performance in transesterification while freezing drying GO is most active for alkylation. The excellent catalytic behavior comes from abundant surface acid sites as well as proper surface functional groups, which can be obtained by selecting appropriate drying process.

Functional analysis of iodotyrosine deiodinase from drosophila melanogaster

PubMed Central

Phatarphekar, Abhishek

2016-01-01

Abstract The flavoprotein iodotyrosine deiodinase (IYD) was first discovered in mammals through its ability to salvage iodide from mono‐ and diiodotyrosine, the by‐products of thyroid hormone synthesis. Genomic information indicates that invertebrates contain homologous enzymes although their iodide requirements are unknown. The catalytic domain of IYD from Drosophila melanogaster has now been cloned, expressed and characterized to determine the scope of its potential catalytic function as a model for organisms that are not associated with thyroid hormone production. Little discrimination between iodo‐, bromo‐, and chlorotyrosine was detected. Their affinity for IYD ranges from 0.46 to 0.62 μM (K d) and their efficiency of dehalogenation ranges from 2.4 – 9 x 103 M−1 s−1 (k cat/K m). These values fall within the variations described for IYDs from other organisms for which a physiological function has been confirmed. The relative contribution of three active site residues that coordinate to the amino acid substrates was subsequently determined by mutagenesis of IYD from Drosophila to refine future annotations of genomic and meta‐genomic data for dehalogenation of halotyrosines. Substitution of the active site glutamate to glutamine was most detrimental to catalysis. Alternative substitution of an active site lysine to glutamine affected substrate affinity to the greatest extent but only moderately affected catalytic turnover. Substitution of phenylalanine for an active site tyrosine was least perturbing for binding and catalysis. PMID:27643701

Decreases in activation energy and substrate affinity in cold-adapted A4-lactate dehydrogenase: evidence from the Antarctic notothenioid fish Chaenocephalus aceratus.

PubMed

Fields, Peter A; Houseman, Daniel E

2004-12-01

Enzyme function is strongly affected by temperature, and orthologs from species adapted to different thermal environments often show temperature compensation in kinetic properties. Antarctic notothenioid fishes live in a habitat of constant, extreme cold (-1.86 +/- 2 degrees C), and orthologs of the enzyme A4-lactate dehydrogenase (A4-LDH) in these species have adapted to this environment through higher catalytic rates, lower Arrhenius activation energies (Ea), and increases in the apparent Michaelis constant for the substrate pyruvate (Km(PYR)). Here, site-directed mutagenesis was used to determine which amino acid substitutions found in A4-LDH of the notothenioid Chaenocephalus aceratus, with respect to orthologs from warm-adapted teleosts, are responsible for these adaptive changes in enzyme function. Km(PYR) was measured in eight single and two double mutants, and Ea was tested in five single and two double mutants in the temperature range 0 degrees C-20 degrees C. Of the four mutants that had an effect on these parameters, two increased Ea but did not affect Km(PYR) (Gly224Ser, Ala310Pro), and two increased both Ea and Km(PYR) (Glu233Met, Gln317Val). The double mutants Glu233Met/Ala310Pro and Glu233Met/Gln317Val increased Km(PYR) and Ea to levels not significantly different from the A4-LDH of a warm temperate fish (Gillichthys mirabilis, habitat temperature 10 degrees C-35 degrees C). The four single mutants are associated with two alpha-helices that move during the catalytic cycle; those that affect Ea but not Km(PYR) are further from the active site than those that affect both parameters. These results provide evidence that (1) cold adaptation in A4-LDH involves changes in mobility of catalytically important molecular structures; (2) these changes may alter activation energy alone or activation energy and substrate affinity together; and (3) the extent to which these parameters are affected may depend on the location of the substitutions within the mobile alpha-helices, perhaps due to differences in proximity to the active site.

Arginine Transcriptional Response Does Not Require Inositol Phosphate Synthesis*

PubMed Central

Bosch, Daniel; Saiardi, Adolfo

2012-01-01

Inositol phosphates are key signaling molecules affecting a large variety of cellular processes. Inositol-polyphosphate multikinase (IPMK) is a central component of the inositol phosphate biosynthetic routes, playing essential roles during development. IPMK phosphorylates inositol 1,4,5-trisphosphate to inositol tetrakisphosphate and subsequently to inositol pentakisphosphate and has also been described to function as a lipid kinase. Recently, a catalytically inactive mammalian IPMK was reported to be involved in nutrient signaling by way of mammalian target of rapamycin and AMP-activated protein kinase. In yeast, the IPMK homologue, Arg82, is the sole inositol-trisphosphate kinase. Arg82 has been extensively studied as part of the transcriptional complex regulating nitrogen sensing, in particular arginine metabolism. Whether this role requires Arg82 catalytic activity has long been a matter of contention. In this study, we developed a novel method for the real time study of promoter strength in vivo and used it to demonstrate that catalytically inactive Arg82 fully restored the arginine-dependent transcriptional response. We also showed that expression in yeast of catalytically active, but structurally very different, mammalian or plant IPMK homologue failed to restore arginine regulation. Our work indicates that inositol phosphates do not regulate arginine-dependent gene expression. PMID:22992733

Selective hydrogenation of phenol to cyclohexanone over Pd@CN (N-doped porous carbon): Role of catalyst reduction method

NASA Astrophysics Data System (ADS)

Hu, Shuo; Yang, Guangxin; Jiang, Hong; Liu, Yefei; Chen, Rizhi

2018-03-01

Selective phenol hydrogenation is a green and sustainable technology to produce cyclohexanone. The work focused on investigating the role of catalyst reduction method in the liquid-phase phenol hydrogenation to cyclohexanone over Pd@CN (N-doped porous carbon). A series of reduction methods including flowing hydrogen reduction, in-situ reaction reduction and liquid-phase reduction were designed and performed. The results highlighted that the reduction method significantly affected the catalytic performance of Pd@CN in the liquid-phase hydrogenation of phenol to cyclohexanone, and the liquid-phase reduction with the addition of appropriate amount of phenol was highly efficient to improve the catalytic activity of Pd@CN. The influence mechanism was explored by a series of characterizations. The results of TEM, XPS and CO chemisorption confirmed that the reduction method mainly affected the size, surface composition and dispersion of Pd in the CN material. The addition of phenol during the liquid-phase reduction could inhibit the aggregation of Pd NPs and promote the reduction of Pd (2+), and then improved the catalytic activity of Pd@CN. The work would aid the development of high-performance Pd@CN catalysts for selective phenol hydrogenation.

Hierarchical Nanoporous Gold-Platinum with Heterogeneous Interfaces for Methanol Electrooxidation

PubMed Central

Xiao, Shuang; Xiao, Fei; Hu, Yuan; Yuan, Songliu; Wang, Shuai; Qian, Lihua; Liu, Yunqi

2014-01-01

The electrocatalysts utilized as the prospective electrodes in fuel cells and high efficient energy conversion devices require both the interconnected channels for efficient electrolyte transportation and the superior catalytic activity with long service life. In this work, nanoporous gold with the rigid skeletons in three dimensions is partially decorated by porous platinum shell containing nanoscale interstitials, aiming to create the heterogeneous gold-platinum interfaces and facilitate the electrolyte transportation as well. In comparison with no catalytic activity of bare nanoporous gold, the catalytic activity of hierarchical nanoporous gold-platinum towards electrochemical oxidation of methanol increases with the loading level of platinum shells, resulting in the highest electrochemical area of 70.4 m2·g−1 after the normalization by the mass of platinum. Heterogeneous gold-platinum interfaces affect the tolerance of the absorbed intermediate species because of the oxidization by the oxygenated species absorbed on the gold surface and the enhanced ion transportation within the porous platinum shell. PMID:24621809

Catalytic Ethanol Dehydration to Ethylene over Nanocrystalline χ- and γ-Al2O3 Catalysts.

PubMed

Janlamool, Jakrapan; Jongsomjit, Bunjerd

2017-01-01

The study is aimed to investigate the combination of nanocrystalline γ- and χ- alumina that displays the attractive chemical and physical properties for the catalytic dehydration of ethanol. The correlation between the acid density and ethanol conversion was observed. The high acid density apparently results in high catalytic activity, especially for the equally mixed γ- and χ- phase alumina (G50C50). In order to obtain a better understanding on how different catalysts would affect the ethylene yield, one of the most powerful techniques such as X-ray photoelectron spectroscopy (XPS) was performed. Hence, the different O 1s surface atoms can be identified and divided into three types including lattice oxygen (O, 530.7 eV), surface hydroxyl (OH, 532.1 eV) and lattice water (H 2 O, 532.9 eV). It was remarkably found that the large amount of O 1s surface atoms in lattice water can result in increased ethylene yield. In summary, the appearance of metastable χ-alumina structure exhibited better catalytic activity and ethylene yield than γ- alumina. Thus, the introduction of metastable χ- alumina structure into γ- alumina enhanced catalytic activity and ethylene yield. As the result, it was found that the G50C50 catalyst exhibits the ethylene yield (80%) at the lowest reaction temperature ca. 250°C among other catalysts.

Function of the family-9 and family-22 carbohydrate-binding modules in a modular beta-1,3-1,4-glucanase/xylanase derived from Clostridium stercorarium Xyn10B.

PubMed

Zhao, Guangshan; Ali, Ehsan; Araki, Rie; Sakka, Makiko; Kimura, Tetsuya; Sakka, Kazuo

2005-08-01

Clostridium stercorarium Xyn10B having hydrolytic activities on xylan and beta-1,3-1,4-glucan is a modular enzyme composed of two family-22 carbohydrate-binding modules (CBMs), a family-10 catalytic module of the glycoside hydrolases, a family-9 CBM, and two S-layer homologous modules, consecutively from the N-terminus. We investigated the function of family-9 and family-22 CBMs in a modular enzyme by comparing the enzymatic properties of a truncated enzyme composed of two family-22 CBMs and the catalytic module (rCBM22-CM), an enzyme composed of the catalytic module and family-9 CBM (rCM-CBM9), an enzyme composed of two family-22 CBMs, the catalytic module, and family-9 CBM (rCBM22-CM-CBM9), and the catalytic module polypeptide (rCM). Although the addition of family-9 CBM to rCM and rCBM22-CM did not significantly change catalytic activity toward xylan and beta-1,3-1,4-glucan, the addition of family-22 CBM to rCM and rCM-CBM9 drastically enhanced catalytic activity toward xylan and especially beta-1,3-1,4-glucan. Furthermore, the addition of family-22 CBM to rCM and rCM-CBM9 shifted the optimum temperature from 65 degrees C to 75 degrees C, but that of family-9 CBM to rCM and rCBM22-CM did not affect the optimum temperature. These facts suggest that the enzyme properties of Xyn10B were mainly dependent on the presence of the family-22 CBMs but not family-9 CBM.

Advantages of a distant cellulase catalytic base.

PubMed

Burgin, Tucker; Ståhlberg, Jerry; Mayes, Heather B

2018-03-30

The inverting glycoside hydrolase Trichoderma reesei ( Hypocrea jecorina ) Cel6A is a promising candidate for protein engineering for more economical production of biofuels. Until recently, its catalytic mechanism had been uncertain: The best candidate residue to serve as a catalytic base, Asp-175, is farther from the glycosidic cleavage site than in other glycoside hydrolase enzymes. Recent unbiased transition path sampling simulations revealed the hydrolytic mechanism for this more distant base, employing a water wire; however, it is not clear why the enzyme employs a more distant catalytic base, a highly conserved feature among homologs across different kingdoms. In this work, we describe molecular dynamics simulations designed to uncover how a base with a longer side chain, as in a D175E mutant, affects procession and active site alignment in the Michaelis complex. We show that the hydrogen bond network is tuned to the shorter aspartate side chain, and that a longer glutamate side chain inhibits procession as well as being less likely to adopt a catalytically productive conformation. Furthermore, we draw comparisons between the active site in Trichoderma reesei Cel6A and another inverting, processive cellulase to deduce the contribution of the water wire to the overall enzyme function, revealing that the more distant catalytic base enhances product release. Our results can inform efforts in the study and design of enzymes by demonstrating how counterintuitive sacrifices in chemical reactivity can have worthwhile benefits for other steps in the catalytic cycle. © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

Distinguishing molecular environments in supported Pt catalysts and their influences on activity and selectivity

NASA Astrophysics Data System (ADS)

Jones, Louis Chin

This thesis entails the synthesis, automated catalytic testing, and in situ molecular characterization of supported Pt and Pt-alloy nanoparticle (NP) catalysts, with emphasis on how to assess the molecular distributions of Pt environments that are affecting overall catalytic activity and selectivity. We have taken the approach of (a) manipulating nucleation and growth of NPs using oxide supports, surfactants, and inorganic complexes to create Pt NPs with uniform size, shape, and composition, (b) automating batch and continuous flow catalytic reaction tests, and (c) characterizing the molecular environments of Pt surfaces using in situ infrared (IR) spectroscopy and solid-state 195Pt NMR. The following will highlight the synthesis and characterization of Ag-doped Pt NPs and their influence on C 2H2 hydrogenation selectivity, and the implementation of advanced solid-state 195Pt NMR techniques to distinguish how distributions of molecular Pt environments vary with nanoparticle size, support, and surface composition.

The role of protein dynamics in the evolution of new enzyme function.

PubMed

Campbell, Eleanor; Kaltenbach, Miriam; Correy, Galen J; Carr, Paul D; Porebski, Benjamin T; Livingstone, Emma K; Afriat-Jurnou, Livnat; Buckle, Ashley M; Weik, Martin; Hollfelder, Florian; Tokuriki, Nobuhiko; Jackson, Colin J

2016-11-01

Enzymes must be ordered to allow the stabilization of transition states by their active sites, yet dynamic enough to adopt alternative conformations suited to other steps in their catalytic cycles. The biophysical principles that determine how specific protein dynamics evolve and how remote mutations affect catalytic activity are poorly understood. Here we examine a 'molecular fossil record' that was recently obtained during the laboratory evolution of a phosphotriesterase from Pseudomonas diminuta to an arylesterase. Analysis of the structures and dynamics of nine protein variants along this trajectory, and three rationally designed variants, reveals cycles of structural destabilization and repair, evolutionary pressure to 'freeze out' unproductive motions and sampling of distinct conformations with specific catalytic properties in bi-functional intermediates. This work establishes that changes to the conformational landscapes of proteins are an essential aspect of molecular evolution and that change in function can be achieved through enrichment of preexisting conformational sub-states.

Effect of the ortho-Hydroxyl Groups on a Bipyridine Ligand of Iridium Complexes for the High-Pressure Gas Generation from the Catalytic Decomposition of Formic Acid.

PubMed

Iguchi, Masayuki; Zhong, Heng; Himeda, Yuichiro; Kawanami, Hajime

2017-12-14

The hydroxyl groups of a 2,2'-bipyridine (bpy) ligand near the metal center activated the catalytic performance of the Ir complex for the dehydrogenation of formic acid at high pressure. The position of the hydroxyl groups on the ligand affected the catalytic durability for the high-pressure H 2 generation through the decomposition of formic acid. The Ir complex with a bipyridine ligand functionalized with para-hydroxyl groups shows a good durability with a constant catalytic activity during the reaction even under high-pressure conditions, whereas deactivation was observed for an Ir complex with a bipyridine ligand with ortho-hydroxyl groups (2). In the presence of high-pressure H 2 , complex 2 decomposed into the ligand and an Ir trihydride complex through the isomerization of the bpy ligand. This work provides the development of a durable catalyst for the high-pressure H 2 production from formic acid. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

LRAT-specific domain facilitates vitamin A metabolism by domain swapping in HRASLS3

DOE PAGES

Golczak, Marcin; Sears, Avery E.; Kiser, Philip D.; ...

2014-11-10

Cellular uptake of vitamin A, production of visual chromophore and triglyceride homeostasis in adipocytes depend on two representatives of the vertebrate N1pC/P60 protein family, lecithin:retinol acyltransferase (LRAT) and HRAS-like tumor suppressor 3 (HRASLS3). Both proteins function as lipid-metabolizing enzymes but differ in their substrate preferences and dominant catalytic activity. The mechanism of this catalytic diversity is not understood. In this paper, by using a gain-of-function approach, we identified a specific sequence responsible for the substrate specificity of N1pC/P60 proteins. A 2.2-Å crystal structure of the HRASLS3-LRAT chimeric enzyme in a thioester catalytic intermediate state revealed a major structural rearrangement accompaniedmore » by three-dimensional domain swapping dimerization not observed in native HRASLS proteins. Structural changes affecting the active site environment contributed to slower hydrolysis of the catalytic intermediate, supporting efficient acyl transfer. Finally, these findings reveal structural adaptation that facilitates selective catalysis and mechanism responsible for diverse substrate specificity within the LRAT-like enzyme family.« less

Boosted surface acidity in TiO2 and Al2O3-TiO2 nanotubes as catalytic supports

NASA Astrophysics Data System (ADS)

Camposeco, R.; Castillo, S.; Mejía-Centeno, Isidro; Navarrete, J.; Nava, N.

2015-11-01

In this study, titanate nanotubes (NT) and titanate nanotubes with alumina (NT-Al) were studied as solid acid catalytic supports to show the relationship between the kind of acidity and catalytic activity. The supports were characterized by XRD, TEM, FTIR, XPS, and tested in the SCR-NO with NH3. It was found that the amount of Brönsted acid sites was maintained and the Lewis acid sites were significantly affected by the addition of alumina (1, 3, 5 and 10 wt.%); such acidity was higher than that of the titanate nanotubes (NT) by two-fold. To confirm the formation of titanate nanotubes and titanate nanotubes with alumina, transmission electron microscopy (TEM) was used. X-ray diffraction (XRD) revealed the formation of the H2Ti4O9·H2O phase. All NT and NT-Al supports presented catalytic activity to remove NO with NH3 under lean conditions, confirming the presence of an important amount of Brönsted and Lewis acid sites in both NT and NT-Al supports.

A comprehensive functional analysis of PTEN mutations: implications in tumor- and autism-related syndromes.

PubMed

Rodríguez-Escudero, Isabel; Oliver, María D; Andrés-Pons, Amparo; Molina, María; Cid, Víctor J; Pulido, Rafael

2011-11-01

The PTEN (phosphatase and tensin homolog) phosphatase is unique in mammals in terms of its tumor suppressor activity, exerted by dephosphorylation of the lipid second messenger PIP(3) (phosphatidylinositol 3,4,5-trisphosphate), which activates the phosphoinositide 3-kinase/Akt/mTOR (mammalian target of rapamycin) oncogenic pathway. Loss-of-function mutations in the PTEN gene are frequent in human cancer and in the germline of patients with PTEN hamartoma tumor-related syndromes (PHTSs). In addition, PTEN is mutated in patients with autism spectrum disorders (ASDs), although no functional information on these mutations is available. Here, we report a comprehensive in vivo functional analysis of human PTEN using a heterologous yeast reconstitution system. Ala-scanning mutagenesis at the catalytic loops of PTEN outlined the critical role of residues within the P-catalytic loop for PIP(3) phosphatase activity in vivo. PTEN mutations that mimic the P-catalytic loop of mammalian PTEN-like proteins (TPTE, TPIP, tensins and auxilins) affected PTEN function variably, whereas tumor- or PHTS-associated mutations targeting the PTEN P-loop produced complete loss of function. Conversely, Ala-substitutions, as well as tumor-related mutations at the WPD- and TI-catalytic loops, displayed partial activity in many cases. Interestingly, a tumor-related D92N mutation was partially active, supporting the notion that the PTEN Asp92 residue might not function as the catalytic general acid. The analysis of a panel of ASD-associated hereditary PTEN mutations revealed that most of them did not substantially abrogate PTEN activity in vivo, whereas most of PHTS-associated mutations did. Our findings reveal distinctive functional patterns among PTEN mutations found in tumors and in the germline of PHTS and ASD patients, which could be relevant for therapy.

Purification and assay of cell-invasive form of calmodulin-sensitive adenylyl cyclase from Bordetella pertussis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Masure, H.R.; Donovan, M.G.; Storm, D.R.

1991-01-01

An invasive form of the CaM-sensitive adenylyl cyclase from Bordetella pertussis can be isolated from bacterial culture supernatants. This isolation is achieved through the use of QAE-Sephadex anion-exchange chromatography. It has been demonstrated that the addition of exogenous Ca{sup 2}{sup +} to the anion-exchange gradient buffers will affect elution from the column and will thereby affect the isolation of invasive adenylyl cyclase. This is probably due to a Ca2(+)-dependent interaction of the catalytic subunit with another component in the culture supernatant. Two peaks of adenylyl cyclase activity are obtained. The Pk1 adenylyl cyclase preparation is able to cause significant increasesmore » in intracellular cAMP levels in animal cells. This increase occurs rapidly and in a dose-dependent manner in both N1E-115 mouse neuroblastoma cells and human erythrocytes. The Pk2 adenylyl cyclase has catalytic activity but is not cell invasive. This material can serve, therefore, as a control to ensure that the cAMP which is measured is, indeed, intracellular. A second control is to add exogenous CaM to the Pk1 adenylyl cyclase preparation. The 45-kDa catalytic subunit-CaM complex is not cell invasive. Although the mechanism for membrane translocation of the adenylyl cyclase is unknown, there is evidence that the adenylyl cyclase enters animal cells by a mechanism distinct from receptor-mediated endocytosis. Calmodulin-sensitive adenylyl cyclase activity can be removed from preparations of the adenylyl cyclase that have been subjected to SDS-polyacrylamide gel electrophoresis. This property of the enzyme has enabled purification of the catalytic subunit to apparent homogeneity. The purified catalytic subunit from culture supernatants has a predicted molecular weight of 45,000. This polypeptide interacts directly with Ca{sup 2}{sup +} and this interaction may be important for its invasion into animal cells.« less

Morphological modification of alpha-MnO2 catalyst for use in Li/air batteries.

PubMed

Park, Min-Sik; Kim, Jae-Hun; Kim, Ki Jae; Jeong, Goojin; Kim, Young-Jun

2013-05-01

Single crystal alpha-MnO2 nanowires and nanopowders have been successfully synthesized in order to facilitate a comparison of their catalytic activity for use in Li-air batteries. The importance of the morphological modification of the alpha-MnO2 catalyst for facilitating electrochemical reactions between Li and O2 is addressed. Distinctive catalytic activity of alpha-MnO2 is observed, which is in line with its different morphologies. The catalytic activity significantly affects the reversible capacity of Li-air batteries. A high aspect ratio, large surface area and good dispersibility of alpha-MnO2 in the nanowire form are advantageous providing larger active surfaces for promoting the fundamental reactions in Li-air batteries. We also introduce a robustly designed air-electrode composed of highly porous carbon and nanostructured alpha-MnO2 catalysts, with employs a metal foam current collector to ensure sufficient air-permeability and to maximize electronic conduction during cycles. Our suggestions should prove helpful in forming a basis for further investigations in developing advanced Li-air batteries.

Zeolite-encapsulated Co(II), Mn(II), Cu(II) and Cr(III) salen complexes as catalysts for efficient selective oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Li, F. H.; Bi, H.; Huang, D. X.; Zhang, M.; Song, Y. B.

2018-01-01

Co(II), Mn(II), Cu(II) and Cr(III) salen type complexes were synthesized in situ in Y zeolite by the reaction of ion-exchanged metal ions with the flexible ligand molecules that had diffused into the cavities. Data of characterization indicates the formation of metal salen complexes in the pores without affecting the zeolite framework structure, the absence of any extraneous species and the geometry of encapsulated complexes. The catalytic activity results show that Cosalcyen Y exhibited higher catalytic activity in the water phase selective oxidation of benzyl alcohol, which could be attributed to their geometry and the steric environment of the metal actives sites.

Effects of Single Nucleotide Polymorphisms on Human N-Acetyltransferase 2 Structure and Dynamics by Molecular Dynamics Simulation

PubMed Central

Rajasekaran, M.; Abirami, Santhanam; Chen, Chinpan

2011-01-01

Background Arylamine N-acetyltransferase 2 (NAT2) is an important catalytic enzyme that metabolizes the carcinogenic arylamines, hydrazine drugs and chemicals. This enzyme is highly polymorphic in different human populations. Several polymorphisms of NAT2, including the single amino acid substitutions R64Q, I114T, D122N, L137F, Q145P, R197Q, and G286E, are classified as slow acetylators, whereas the wild-type NAT2 is classified as a fast acetylator. The slow acetylators are often associated with drug toxicity and efficacy as well as cancer susceptibility. The biological functions of these 7 mutations have previously been characterized, but the structural basis behind the reduced catalytic activity and reduced protein level is not clear. Methodology/Principal Findings We performed multiple molecular dynamics simulations of these mutants as well as NAT2 to investigate the structural and dynamical effects throughout the protein structure, specifically the catalytic triad, cofactor binding site, and the substrate binding pocket. None of these mutations induced unfolding; instead, their effects were confined to the inter-domain, domain 3 and 17-residue insert region, where the flexibility was significantly reduced relative to the wild-type. Structural effects of these mutations propagate through space and cause a change in catalytic triad conformation, cofactor binding site, substrate binding pocket size/shape and electrostatic potential. Conclusions/Significance Our results showed that the dynamical properties of all the mutant structures, especially in inter-domain, domain 3 and 17-residue insert region were affected in the same manner. Similarly, the electrostatic potential of all the mutants were altered and also the functionally important regions such as catalytic triad, cofactor binding site, and substrate binding pocket adopted different orientation and/or conformation relative to the wild-type that may affect the functions of the mutants. Overall, our study may provide the structural basis for reduced catalytic activity and protein level, as was experimentally observed for these polymorphisms. PMID:21980537

Structural Basis for the Catalytic Activity of Human Serine/Threonine Protein Phosphatase-5

NASA Technical Reports Server (NTRS)

Swingle, M. R.; Honkanen, R.; Ciszak, E. M.

2004-01-01

Serinehhreonine protein phosphatase-5 (PP5) affects many signaling networks that regulate cell growth and cellular responses to stress. Here we report the crystal structure of the PP5 catalytic domain (PP5c) at a resolution of 1.6 A. From this structure we resolved the mechanism for PP5-mediated hydrolysis of phosphoprotein substrates, which requires the precise positioning of two metal ions within a con served Aspn-271-M(sub 1):M(sub 2)-W(sup 1)-His-427-His-304-Asp-274 catalytic motif. The structure of PPSc provides a structural basis for explaining the exceptional catalytic proficiency of protein phosphatases, which are among the most powerful known catalysts. Resolution of the entire C-terminus revealed a novel subdomain, and the structure of the PP5c should also aid development of type-specific inhibitors.

Immobilized Cytochrome P450 2C9 (CYP2C9): Applications for Metabolite Generation, Monitoring Protein-Protein Interactions, and Improving In-vivo Predictions Using Enhanced In-vitro Models

NASA Astrophysics Data System (ADS)

Wollenberg, Lance A.

Cytochrome P450 (P450) enzymes are a family of oxoferroreductase enzymes containing a heme moiety and are well known to be involved in the metabolism of a wide variety of endogenous and xenobiotic materials. It is estimated that roughly 75% of all pharmaceutical compounds are metabolized by these enzymes. Traditional reconstituted in-vitro incubation studies using recombinant P450 enzymes are often used to predict in-vivo kinetic parameters of a drug early in development. However, in many cases, these reconstituted incubations are prone to aggregation which has been shown to affect the catalytic activity of an enzyme. Moreover, the presence of other isoforms of P450 enzymes present in a metabolic incubation, as is the case with microsomal systems, may affect the catalytic activity of an enzyme through isoform-specific protein-protein interactions. Both of these effects may result in inaccurate prediction of in-vivo drug metabolism using in-vitro experiments. Here we described the development of immobilized P450 constructs designed to elucidate the effects of aggregation and protein-protein interactions between P450 isoforms on catalytic activities. The long term objective of this project is to develop a system to control the oligomeric state of Cytochrome P450 enzymes to accurately elucidate discrepancies between in vitro reconstituted systems and actual in vivo drug metabolism for the precise prediction of metabolic activity. This approach will serve as a system to better draw correlations between in-vivo and in-vitro drug metabolism data. The central hypothesis is that Cytochrome P450 enzymes catalytic activity can be altered by protein-protein interactions occurring between Cytochrome P450 enzymes involved in drug metabolism, and is dependent on varying states of protein aggregation. This dissertation explains the details of the construction and characterization of a nanostructure device designed to control the state of aggregation of a P450 enzyme. Moreover, applications of immobilized P450 enzyme constructs will also be used for monitoring protein-protein interaction and metabolite production with the use of immobilized-P450 bioreactor constructs. This work provides insight into the effect on catalytic activity caused by both P450 aggregation as well as isoform-specific protein-protein interactions and provides insight in the production of biosynthetically produced drug metabolites

Accurate placement of substrate RNA by Gar1 in H/ACA RNA-guided pseudouridylation.

PubMed

Wang, Peng; Yang, Lijiang; Gao, Yi Qin; Zhao, Xin Sheng

2015-09-03

H/ACA RNA-guided ribonucleoprotein particle (RNP), the most complicated RNA pseudouridylase so far known, uses H/ACA guide RNA for substrate capture and four proteins (Cbf5, Nop10, L7Ae and Gar1) for pseudouridylation. Although it was shown that Gar1 not only facilitates the product release, but also enhances the catalytic activity, the chemical role that Gar1 plays in this complicated machinery is largely unknown. Kinetics measurement on Pyrococcus furiosus RNPs at different temperatures making use of fluorescence anisotropy showed that Gar1 reduces the catalytic barrier through affecting the activation entropy instead of enthalpy. Site-directed mutagenesis combined with molecular dynamics simulations demonstrated that V149 in the thumb loop of Cbf5 is critical in placing the target uridine to the right position toward catalytic D85 of Cbf5. The enzyme elegantly aligns the position of uridine in the catalytic site with the help of Gar1. In addition, conversion of uridine to pseudouridine results in a rigid syn configuration of the target nucleotide in the active site and causes Gar1 to pull out the thumb. Both factors guarantee the efficient release of the product. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

Improved catalytic efficiency, thermophilicity, anti-salt and detergent tolerance of keratinase KerSMD by partially truncation of PPC domain

PubMed Central

Fang, Zhen; Zhang, Juan; Du, Guocheng; Chen, Jian

2016-01-01

The keratinase from Stenotrophomonas maltophilia (KerSMD) is known for its high activity and pH stability in keratin degradation. However, catalytic efficiency and detergent tolerability need to be improved in order to be used for industrial application. In this work, we obtained several keratinase variants with enhanced catalytic efficiency, thermophilicity, and anti-salt and detergent tolerability by partially truncating the PPC domain of KerSMD. The variants all showed improved catalytic efficiency to synthetic substrate AAPF, with the V355 variant having the highest kcat /Km value of 143.6 s−1 mM−1. The truncation of keratinase had little effect on alkaline stability but obviously decreased collagenase activity, developing its potential application in leather treatment. The variants V380, V370, and V355 were thermophilic, with a 1.7-fold enhancement of keratinlytic activity at 60 °C when compared to the wild type. The entire truncation of PPC domain obtained the variant V355 with improved tolerance to alkalinity, salt, chaotropic agents, and detergents. The V355 variant showed more than a 40% improvement in activity under 15% (w/v) NaCl or 4% (w/v) SDS solution, showing excellent stability under harsh washing and unhairing conditions. Our work investigated how protein engineering affects the function of PPC domain of KerSMD. PMID:27298079

Improved catalytic efficiency, thermophilicity, anti-salt and detergent tolerance of keratinase KerSMD by partially truncation of PPC domain.

PubMed

Fang, Zhen; Zhang, Juan; Du, Guocheng; Chen, Jian

2016-06-14

The keratinase from Stenotrophomonas maltophilia (KerSMD) is known for its high activity and pH stability in keratin degradation. However, catalytic efficiency and detergent tolerability need to be improved in order to be used for industrial application. In this work, we obtained several keratinase variants with enhanced catalytic efficiency, thermophilicity, and anti-salt and detergent tolerability by partially truncating the PPC domain of KerSMD. The variants all showed improved catalytic efficiency to synthetic substrate AAPF, with the V355 variant having the highest kcat /Km value of 143.6 s(-1) mM(-1). The truncation of keratinase had little effect on alkaline stability but obviously decreased collagenase activity, developing its potential application in leather treatment. The variants V380, V370, and V355 were thermophilic, with a 1.7-fold enhancement of keratinlytic activity at 60 °C when compared to the wild type. The entire truncation of PPC domain obtained the variant V355 with improved tolerance to alkalinity, salt, chaotropic agents, and detergents. The V355 variant showed more than a 40% improvement in activity under 15% (w/v) NaCl or 4% (w/v) SDS solution, showing excellent stability under harsh washing and unhairing conditions. Our work investigated how protein engineering affects the function of PPC domain of KerSMD.

Surface-active ionic liquids for palladium-catalysed cross coupling in water: effect of ionic liquid concentration on the catalytically active species† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c7ra07757b

PubMed Central

Taskin, Meltem; Cognigni, Alice; Zirbs, Ronald; Reimhult, Erik

2017-01-01

We report the design and synthesis of surface-active ionic liquids for application in palladium-catalyzed cross coupling reactions. A series of dodecylimidazolium-based ionic liquids were applied as additives in the Heck reaction of ethyl acrylate and iodobenzene, and high yields of >90% could be obtained in water without the addition of further ligands. Our results indicate that the ionic liquid concentration in water is the key factor affecting the formation of the catalytically active species and hence the yield. Moreover, imidazolium-based ionic liquids that are able to form a carbene species differ significantly from conventional cationic surfactants, as a concentration dependent formation of the N-heterocyclic carbene complex was observed. PMID:29308189

Characterization of C-terminally engineered laccases.

PubMed

Liu, Yingli; Cusano, Angela Maria; Wallace, Erin C; Mekmouche, Yasmina; Ullah, Sana; Robert, Viviane; Tron, Thierry

2014-08-01

Extremities of proteins are potent sites for functionalization. Carboxy terminus variants of the Trametes sp. strain C30 LAC3 laccase were generated and produced in Saccharomyces cerevisiae. A variant deleted of the last 13 residues (CΔ) and its 6 His tagged counterpart (CΔ6H) were found active enzymes. The production of CΔ6H resulted in the synthesis of a unusually high proportion of highly glycosylated forms of the enzyme therefore allowing the additional purification of a hyper-glycosylated form of CΔ6H noted CΔ6Hh. Properties of CΔ, CΔ6H and CΔ6Hh were compared. Globally, LAC3 catalytic efficiency was moderately affected by terminal modifications except in CΔ for which the kcat/KM ratio decreased 4 fold (with syringaldazine as substrate) and 10 fold (with ABTS as substrate) respectively. The catalytic parameters kcat and KM of CΔ6H and CΔ6Hh were found to be strictly comparable revealing that over glycosylation does not affect the enzyme catalytic efficiency. To the contrary, in vitro deglycosylation of laccase drastically reduced its activity. So, despite a complex glycosylated pattern observed for some of the variant enzymes, terminal sequences of laccases appear to be appropriate sites for the functionalization/immobilization of laccase. Copyright © 2014 Elsevier B.V. All rights reserved.

Antioxidant activity of selenenamide-based mimic as a function of the aromatic thiols nucleophilicity, a DFT-SAPE model.

PubMed

Kheirabadi, Ramesh; Izadyar, Mohammad

2018-05-18

The mechanism of action of the selenenamide 1 as a mimic of the glutathione peroxidase (GPx) was investigated by the density functional theory. The solvent-assisted proton exchange procedure was applied to model the catalytic behavior and antioxidant activity of this mimic. To have an insight into the charge transfer effect, different aromatic thiols, including electron donating substituents on the phenyl ring were considered. The catalytic behavior of the selenenamide was modeled in a four-step mechanism, described by the oxidation of the mimic, the reduction of the obtained product, selenoxide, the reduction of the selenenylsulfide and dehydration of selenenic acid. On the basis of the activation parameters, the final step of the proposed mechanism is the rate determining states of the catalytic cycle. Turnover frequency (TOF) analysis showed that the electron donating groups at the para-position of the phenyl ring of the PhSH do not affect the catalytic activity of the selenenamide in contrast to p-methyl thiophenol which indicates the highest nucleophilicity. The evaluation of the electronic contribution of the various donating groups on the phenyl ring of the aromatic thiols shows that the antioxidant activity of the selenenamide sufficiently increases in the presence of the electron-donating substitutions. Finally, the charge transfer process at the rate-determining state was investigated based on the natural bond orbital analysis. Copyright © 2018 Elsevier Ltd. All rights reserved.

Functional characterization of the non-catalytic ectodomains of the nucleotide pyrophosphatase/phosphodiesterase NPP1.

PubMed Central

Gijsbers, Rik; Ceulemans, Hugo; Bollen, Mathieu

2003-01-01

The ubiquitous nucleotide pyrophosphatases/phosphodiesterases NPP1-3 consist of a short intracellular N-terminal domain, a single transmembrane domain and a large extracellular part, comprising two somatomedin-B-like domains, a catalytic domain and a poorly defined C-terminal domain. We show here that the C-terminal domain of NPP1-3 is structurally related to a family of DNA/RNA non-specific endonucleases. However, none of the residues that are essential for catalysis by the endonucleases are conserved in NPP1-NPP3, suggesting that the nuclease-like domain of NPP1-3 does not represent a second catalytic domain. Truncation analysis revealed that the nuclease-like domain of NPP1 is required for protein stability, for the targeting of NPP1 to the plasma membrane and for the expression of catalytic activity. We also demonstrate that 16 conserved cysteines in the somatomedin-B-like domains of NPP1, in concert with two flanking cysteines, mediate the dimerization of NPP1. The K173Q polymorphism of NPP1, which maps to the second somatomedin-B-like domain and has been associated with the aetiology of insulin resistance, did not affect the dimerization or catalytic activity of NPP1, and did not endow NPP1 with an affinity for the insulin receptor. Our data suggest that the non-catalytic ectodomains contribute to the subunit structure, stability and function of NPP1-3. PMID:12533192

To what extent do structural changes in catalytic metal sites affect enzyme function?

PubMed

Valasatava, Yana; Rosato, Antonio; Furnham, Nicholas; Thornton, Janet M; Andreini, Claudia

2018-02-01

About half of known enzymatic reactions involve metals. Enzymes belonging to the same superfamily often evolve to catalyze different reactions on the same structural scaffold. The work presented here investigates how functional differentiation, within superfamilies that contain metalloenzymes, relates to structural changes at the catalytic metal site. In general, when the catalytic metal site is unchanged across the enzymes of a superfamily, the functional differentiation within the superfamily tends to be low and the mechanism conserved. Conversely, all types of structural changes in the metal binding site are observed for superfamilies with high functional differentiation. Overall, the catalytic role of the metal ions appears to be one of the most conserved features of the enzyme mechanism within metalloenzyme superfamilies. In particular, when the catalytic role of the metal ion does not involve a redox reaction (i.e. there is no exchange of electrons with the substrate), this role is almost always maintained even when the site undergoes significant structural changes. In these enzymes, functional diversification is most often associated with modifications in the surrounding protein matrix, which has changed so much that the enzyme chemistry is significantly altered. On the other hand, in more than 50% of the examples where the metal has a redox role in catalysis, changes at the metal site modify its catalytic role. Further, we find that there are no examples in our dataset where metal sites with a redox role are lost during evolution. In this paper we investigate how functional diversity within superfamilies of metalloenzymes relates to structural changes at the catalytic metal site. Evolution tends to strictly conserve the metal site. When changes occur, they do not modify the catalytic role of non-redox metals whereas they affect the role of redox-active metals. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Changes in the quaternary structure of phosphoenolpyruvate carboxylase induced by ionic strength affect its catalytic activity.

PubMed

Wagner, R; Gonzalez, D H; Podesta, F E; Andreo, C S

1987-05-04

Phosphoenolpyruvate carboxylase from maize leaves dissociated into dimers and/or monomers when exposed to increasing ionic strength (e.g. 200-400 mM NaCl) as indicated by gel filtration experiments. Changes in the oligomerization state were dependent on pH, time of preincubation with salt and protein concentration. A dissociation into dimers and monomers was observed at pH 8, while at pH 7 dissociation into the dimeric form only was observed. Exposure of the enzyme to higher ionic strength decreased the activity in a time-dependent manner. Turnover conditions and glucose 6-phosphate protected the carboxylase from the decay in activity, which was faster at pH 7 than at pH 8. The results suggest that changes in activity of the enzyme, following exposure to high ionic strength, are the consequence of dissociation. Tetrameric and dimeric forms of the phosphoenolpyruvate carboxylase seemingly reveal different catalytic properties. We suggest that the distinct catalytic properties of the different oligomeric species of phosphoenolpyruvate carboxylase and changes in the equilibrium between them could be the molecular basis for an effective regulation of metabolite levels by this key enzyme of C4 plants.

Identification of the catalytic triad of the lipase/acyltransferase from Aeromonas hydrophila.

PubMed Central

Brumlik, M J; Buckley, J T

1996-01-01

Aeromonas hydrophila secretes a lipolytic enzyme that has several properties in common with the mammalian enzyme lecithin-cholesterol acyltransferase. We have recently shown that it is a member of a newly described group of proteins that contain five similar blocks of sequence arranged in the same order in their primary structures (C. Upton and J. T. Buckley, Trends Biochem. Sci. 233:178-179, 1995). Assuming that, like other lipases, these enzymes have a Ser-Asp-His catalytic triad, we used these blocks to predict which aspartic acid and histidine would be at the active site of the Aeromonas enzyme. Targeted residues were replaced with other amino acids by site-directed mutagenesis, and the effects on secretion and activity were assessed. Changing His-291 to asparagine completely abolished enzyme activity, although secretion by the bacteria was not affected. Only very small amounts of the D116N mutant appeared in the culture supernatant, likely because it is sensitive to periplasmic proteases it encounters en route. Assays of crude preparations containing this variant showed no detectable enzyme activity. We conclude that, together with Ser-16, which we have identified previously, Asp-116 and His-291 compose the catalytic triad of the enzyme. PMID:8606184

Improved activity of α-chymotrypsin on silica particles - A high-pressure stopped-flow study.

PubMed

Schuabb, Vitor; Winter, Roland; Czeslik, Claus

2016-11-01

Pressure is well known to affect the catalytic rate of enzymes dissolved in solution. To better understand enzyme kinetics at aqueous-solid interfaces, we have carried out a high-pressure stopped-flow activity study of α-chymotrypsin (α-CT) that is adsorbed on silica particles and, for comparison, dissolved in solution. The enzyme reaction was modulated using pressures up to 2000bar and recorded using the high-pressure stopped-flow technique. The results indicate an 8-fold enhancement of the turnover number upon α-CT adsorption and a further increase of the catalytic rate in the pressure range up to 1000bar. From the pressure dependence of the catalytic rate, apparent activation volumes have been determined. In the adsorbed state of α-CT, a pronounced change of the activation volume is found with increasing pressure. Furthermore, owing to suppression of its autolysis, a significantly longer storage time of α-CT can be achieved when the enzyme is adsorbed on silica particles. The results obtained are discussed in terms of a surface-induced selection of conformational substates of the enzyme-substrate complex. Copyright © 2016 Elsevier B.V. All rights reserved.

Evolution of Active Sites in Pt-Based Nanoalloy Catalysts for the Oxidation of Carbonaceous Species by Combined in Situ Infrared Spectroscopy and Total X-ray Scattering.

PubMed

Petkov, Valeri; Maswadeh, Yazan; Lu, Aolin; Shan, Shiyao; Kareem, Haval; Zhao, Yinguang; Luo, Jin; Zhong, Chuan-Jian; Beyer, Kevin; Chapman, Karena

2018-04-04

We present results from combined in situ infrared spectroscopy and total X-ray scattering studies on the evolution of catalytically active sites in exemplary binary and ternary Pt-based nanoalloys during a sequence of CO oxidation-reactivation-CO oxidation reactions. We find that when within a particular compositional range, the fresh nanoalloys may exhibit high catalytic activity for low-temperature CO oxidation. Using surface-specific atomic pair distribution functions (PDFs) extracted from the in situ total X-ray scattering data, we find that, regardless of their chemical composition and initial catalytic activity, the fresh nanoalloys suffer a significant surface structural disorder during CO oxidation. Upon reactivation in oxygen atmosphere, the surface of used nanoalloy catalysts both partially oxidizes and orders. Remarkably, it largely retains its structural state when the nanoalloys are reused as CO oxidation catalysts. The seemingly inverse structural changes of studied nanoalloy catalysts occurring under CO oxidation and reactivation conditions affect the active sites on their surface significantly. In particular, through different mechanisms, both appear to reduce the CO binding strength to the nanoalloy's surface and thus increase the catalytic stability of the nanoalloys. The findings provide clues for further optimization of nanoalloy catalysts for the oxidation of carbonaceous species through optimizing their composition, activation, and reactivation. Besides, the findings demonstrate the usefulness of combined in situ infrared spectroscopy and total X-ray scattering coupled to surface-specific atomic PDF analysis to the ongoing effort to produce advanced catalysts for environmentally and technologically important applications.

Application of the principle of linked functions to ATP-driven ion pumps: kinetics of activation by ATP.

PubMed Central

Reynolds, J A; Johnson, E A; Tanford, C

1985-01-01

If a ligand binds with unequal affinity to two distinct states of a protein, then the equilibrium between the two states becomes a function of the concentration of the ligand. A necessary consequence is that the ligand must also affect the forward and/or reverse rate constants for transition between the two states. For an enzyme or transport protein with such a transition as a slow step in the catalytic cycle, the overall rate also becomes a function of ligand concentration. These conclusions are independent of whether or not the ligand is a direct participant in the reaction. If it is a direct participant, then the kinetic effect arising from the principle of linked functions is distinct from the direct catalytic effect. These principles suffice to account for the biphasic response of the hydrolytic activity of ATP-driven ion pumps to the concentration of ATP, without the need to invoke more than one ATP binding site per catalytic center. PMID:2987939

An arginine-aspartate network in the active site of bacterial TruB is critical for catalyzing pseudouridine formation.

PubMed

Friedt, Jenna; Leavens, Fern M V; Mercier, Evan; Wieden, Hans-Joachim; Kothe, Ute

2014-04-01

Pseudouridine synthases introduce the most common RNA modification and likely use the same catalytic mechanism. Besides a catalytic aspartate residue, the contributions of other residues for catalysis of pseudouridine formation are poorly understood. Here, we have tested the role of a conserved basic residue in the active site for catalysis using the bacterial pseudouridine synthase TruB targeting U55 in tRNAs. Substitution of arginine 181 with lysine results in a 2500-fold reduction of TruB's catalytic rate without affecting tRNA binding. Furthermore, we analyzed the function of a second-shell aspartate residue (D90) that is conserved in all TruB enzymes and interacts with C56 of tRNA. Site-directed mutagenesis, biochemical and kinetic studies reveal that this residue is not critical for substrate binding but influences catalysis significantly as replacement of D90 with glutamate or asparagine reduces the catalytic rate 30- and 50-fold, respectively. In agreement with molecular dynamics simulations of TruB wild type and TruB D90N, we propose an electrostatic network composed of the catalytic aspartate (D48), R181 and D90 that is important for catalysis by fine-tuning the D48-R181 interaction. Conserved, negatively charged residues similar to D90 are found in a number of pseudouridine synthases, suggesting that this might be a general mechanism.

An arginine-aspartate network in the active site of bacterial TruB is critical for catalyzing pseudouridine formation

PubMed Central

Friedt, Jenna; Leavens, Fern M. V.; Mercier, Evan; Wieden, Hans-Joachim; Kothe, Ute

2014-01-01

Pseudouridine synthases introduce the most common RNA modification and likely use the same catalytic mechanism. Besides a catalytic aspartate residue, the contributions of other residues for catalysis of pseudouridine formation are poorly understood. Here, we have tested the role of a conserved basic residue in the active site for catalysis using the bacterial pseudouridine synthase TruB targeting U55 in tRNAs. Substitution of arginine 181 with lysine results in a 2500-fold reduction of TruB’s catalytic rate without affecting tRNA binding. Furthermore, we analyzed the function of a second-shell aspartate residue (D90) that is conserved in all TruB enzymes and interacts with C56 of tRNA. Site-directed mutagenesis, biochemical and kinetic studies reveal that this residue is not critical for substrate binding but influences catalysis significantly as replacement of D90 with glutamate or asparagine reduces the catalytic rate 30- and 50-fold, respectively. In agreement with molecular dynamics simulations of TruB wild type and TruB D90N, we propose an electrostatic network composed of the catalytic aspartate (D48), R181 and D90 that is important for catalysis by fine-tuning the D48-R181 interaction. Conserved, negatively charged residues similar to D90 are found in a number of pseudouridine synthases, suggesting that this might be a general mechanism. PMID:24371284

Structure-Function Analysis of Rny1 in tRNA Cleavage and Growth Inhibition

PubMed Central

Luhtala, Natalie; Parker, Roy

2012-01-01

T2 ribonucleases are conserved nucleases that affect a variety of processes in eukaryotic cells including the regulation of self-incompatibility by S-RNases in plants, modulation of host immune cell responses by viral and schistosome T2 enzymes, and neurological development and tumor progression in humans. These roles for RNaseT2’s can be due to catalytic or catalytic-independent functions of the molecule. Despite this broad importance, the features of RNaseT2 proteins that modulate catalytic and catalytic-independent functions are poorly understood. Herein, we analyze the features of Rny1 in Saccharomyces cerevisiae to determine the requirements for cleaving tRNA in vivo and for inhibiting cellular growth in a catalytic-independent manner. We demonstrate that catalytic-independent inhibition of growth is a combinatorial property of the protein and is affected by a fungal-specific C-terminal extension, the conserved catalytic core, and the presence of a signal peptide. Catalytic functions of Rny1 are independent of the C-terminal extension, are affected by many mutations in the catalytic core, and also require a signal peptide. Biochemical flotation assays reveal that in rny1Δ cells, some tRNA molecules associate with membranes suggesting that cleavage of tRNAs by Rny1 can involve either tRNA association with, or uptake into, membrane compartments. PMID:22829915

Chemical imaging of Fischer-Tropsch catalysts under operating conditions

PubMed Central

Price, Stephen W. T.; Martin, David J.; Parsons, Aaron D.; Sławiński, Wojciech A.; Vamvakeros, Antonios; Keylock, Stephen J.; Beale, Andrew M.; Mosselmans, J. Frederick W.

2017-01-01

Although we often understand empirically what constitutes an active catalyst, there is still much to be understood fundamentally about how catalytic performance is influenced by formulation. Catalysts are often designed to have a microstructure and nanostructure that can influence performance but that is rarely considered when correlating structure with function. Fischer-Tropsch synthesis (FTS) is a well-known and potentially sustainable technology for converting synthetic natural gas (“syngas”: CO + H2) into functional hydrocarbons, such as sulfur- and aromatic-free fuel and high-value wax products. FTS catalysts typically contain Co or Fe nanoparticles, which are often optimized in terms of size/composition for a particular catalytic performance. We use a novel, “multimodal” tomographic approach to studying active Co-based catalysts under operando conditions, revealing how a simple parameter, such as the order of addition of metal precursors and promoters, affects the spatial distribution of the elements as well as their physicochemical properties, that is, crystalline phase and crystallite size during catalyst activation and operation. We show in particular how the order of addition affects the crystallinity of the TiO2 anatase phase, which in turn leads to the formation of highly intergrown cubic close-packed/hexagonal close-packed Co nanoparticles that are very reactive, exhibiting high CO conversion. This work highlights the importance of operando microtomography to understand the evolution of chemical species and their spatial distribution before any concrete understanding of impact on catalytic performance can be realized. PMID:28345057

Role of asparagine 152 in catalysis of beta-lactam hydrolysis by Escherichia coli AmpC beta-lactamase studied by site-directed mutagenesis.

PubMed

Dubus, A; Normark, S; Kania, M; Page, M G

1995-06-13

The role of asparagine 152 in the catalytic mechanism of Escherichia coli AmpC beta-lactamase has been investigated by site-directed mutagenesis. The residue has been replaced by aspartic acid, glutamic acid, histidine, and leucine. All the substitutions had similar effects on the activity toward substrates and inhibitors. The rate of substrate hydrolysis decreased by factors of 500-5000. The rates of both acylation (2-50-fold decrease) and deacylation (50-500-fold decrease) were affected, indicating a role for Asn152 in both processes. The wild-type AmpC beta-lactamase appears to exist as an equilibrium mixture of two forms, identified by their different kinetic properties. The Asn152 mutations affected the activity of the slow-reacting form much more than that of the fast-reacting form, but they did not appear to affect the interconversion of these two kinetic forms. Comparison of these observations with results obtained with mutation of the equivalent residues in other classes of penicillin-sensitive enzyme indicates that there are quite profound differences between the catalytic mechanisms of these enzymes despite a high degree of conservation of amino acids in the active center, and of the overall three-dimensional structure.

A novel familial mutation in the PCSK1 gene that alters the oxyanion hole residue of proprotein convertase 1/3 and impairs its enzymatic activity.

PubMed

Wilschanski, Michael; Abbasi, Montaser; Blanco, Elias; Lindberg, Iris; Yourshaw, Michael; Zangen, David; Berger, Itai; Shteyer, Eyal; Pappo, Orit; Bar-Oz, Benjamin; Martín, Martin G; Elpeleg, Orly

2014-01-01

Four siblings presented with congenital diarrhea and various endocrinopathies. Exome sequencing and homozygosity mapping identified five regions, comprising 337 protein-coding genes that were shared by three affected siblings. Exome sequencing identified a novel homozygous N309K mutation in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, encoding the neuroendocrine convertase 1 precursor (PC1/3) which was recently reported as a cause of Congenital Diarrhea Disorder (CDD). The PCSK1 mutation affected the oxyanion hole transition state-stabilizing amino acid within the active site, which is critical for appropriate proprotein maturation and enzyme activity. Unexpectedly, the N309K mutant protein exhibited normal, though slowed, prodomain removal and was secreted from both HEK293 and Neuro2A cells. However, the secreted enzyme showed no catalytic activity, and was not processed into the 66 kDa form. We conclude that the N309K enzyme is able to cleave its own propeptide but is catalytically inert against in trans substrates, and that this variant accounts for the enteric and systemic endocrinopathies seen in this large consanguineous kindred.

A Novel Familial Mutation in the PCSK1 Gene That Alters the Oxyanion Hole Residue of Proprotein Convertase 1/3 and Impairs Its Enzymatic Activity

PubMed Central

Wilschanski, Michael; Abbasi, Montaser; Blanco, Elias; Lindberg, Iris; Yourshaw, Michael; Zangen, David; Berger, Itai; Shteyer, Eyal; Pappo, Orit; Bar-Oz, Benjamin; Martín, Martin G.; Elpeleg, Orly

2014-01-01

Four siblings presented with congenital diarrhea and various endocrinopathies. Exome sequencing and homozygosity mapping identified five regions, comprising 337 protein-coding genes that were shared by three affected siblings. Exome sequencing identified a novel homozygous N309K mutation in the proprotein convertase subtilisin/kexin type 1 (PCSK1) gene, encoding the neuroendocrine convertase 1 precursor (PC1/3) which was recently reported as a cause of Congenital Diarrhea Disorder (CDD). The PCSK1 mutation affected the oxyanion hole transition state-stabilizing amino acid within the active site, which is critical for appropriate proprotein maturation and enzyme activity. Unexpectedly, the N309K mutant protein exhibited normal, though slowed, prodomain removal and was secreted from both HEK293 and Neuro2A cells. However, the secreted enzyme showed no catalytic activity, and was not processed into the 66 kDa form. We conclude that the N309K enzyme is able to cleave its own propeptide but is catalytically inert against in trans substrates, and that this variant accounts for the enteric and systemic endocrinopathies seen in this large consanguineous kindred. PMID:25272002

Structural, Functional, and Clinical Characterization of a Novel PTPN11 Mutation Cluster Underlying Noonan Syndrome.

PubMed

Pannone, Luca; Bocchinfuso, Gianfranco; Flex, Elisabetta; Rossi, Cesare; Baldassarre, Giuseppina; Lissewski, Christina; Pantaleoni, Francesca; Consoli, Federica; Lepri, Francesca; Magliozzi, Monia; Anselmi, Massimiliano; Delle Vigne, Silvia; Sorge, Giovanni; Karaer, Kadri; Cuturilo, Goran; Sartorio, Alessandro; Tinschert, Sigrid; Accadia, Maria; Digilio, Maria C; Zampino, Giuseppe; De Luca, Alessandro; Cavé, Hélène; Zenker, Martin; Gelb, Bruce D; Dallapiccola, Bruno; Stella, Lorenzo; Ferrero, Giovanni B; Martinelli, Simone; Tartaglia, Marco

2017-04-01

Germline mutations in PTPN11, the gene encoding the Src-homology 2 (SH2) domain-containing protein tyrosine phosphatase (SHP2), cause Noonan syndrome (NS), a relatively common, clinically variable, multisystem disorder. Here, we report on the identification of five different PTPN11 missense changes affecting residues Leu 261 , Leu 262 , and Arg 265 in 16 unrelated individuals with clinical diagnosis of NS or with features suggestive for this disorder, specifying a novel disease-causing mutation cluster. Expression of the mutant proteins in HEK293T cells documented their activating role on MAPK signaling. Structural data predicted a gain-of-function role of substitutions at residues Leu 262 and Arg 265 exerted by disruption of the N-SH2/PTP autoinhibitory interaction. Molecular dynamics simulations suggested a more complex behavior for changes affecting Leu 261 , with possible impact on SHP2's catalytic activity/selectivity and proper interaction of the PTP domain with the regulatory SH2 domains. Consistent with that, biochemical data indicated that substitutions at codons 262 and 265 increased the catalytic activity of the phosphatase, while those affecting codon 261 were only moderately activating but impacted substrate specificity. Remarkably, these mutations underlie a relatively mild form of NS characterized by low prevalence of cardiac defects, short stature, and cognitive and behavioral issues, as well as less evident typical facial features. © 2017 WILEY PERIODICALS, INC.

Identification of N-Terminal Lobe Motifs that Determine the Kinase Activity of the Catalytic Domains and Regulatory Strategies of Src and Csk Protein Tyrosine Kinases†

PubMed Central

Huang, Kezhen; Wang, Yue-Hao; Brown, Alex; Sun, Gongqin

2009-01-01

Csk and Src protein tyrosine kinases are structurally homologous, but use opposite regulatory strategies. The isolated catalytic domain of Csk is intrinsically inactive and is activated by interactions with the regulatory SH3 and SH2 domains, while the isolated catalytic domain of Src is intrinsically active and is suppressed by interactions with the regulatory SH3 and SH2 domains. The structural basis for why one isolated catalytic domain is intrinsically active while the other is inactive is not clear. In this current study, we identify the structural elements in the N-terminal lobe of the catalytic domain that render the Src catalytic domain active. These structural elements include the α-helix C region, a β-turn between the β-4 and β-5 strands, and an Arg residue at the beginning of the catalytic domain. These three motifs interact with each other to activate the Src catalytic domain, but the equivalent motifs in Csk directly interact with the regulatory domains that are important for Csk activation. The Src motifs can be grafted to the Csk catalytic domain to obtain an active Csk catalytic domain. These results, together with available Src and Csk tertiary structures, reveal an important structural switch that determines the kinase activity of a catalytic domain and dictates the regulatory strategy of a kinase. PMID:19244618

Nitrate reduction over a Pd-Cu/MWCNT catalyst: application to a polluted groundwater.

PubMed

Soares, Olivia Salomé G P; Orfão, José J M; Gallegos-Suarez, Esteban; Castillejos, Eva; Rodríguez-Ramos, Inmaculada; Pereira, Manuel Fernando R

2012-01-01

The influence of the presence of inorganic and organic matter during the catalytic reduction of nitrate in a local groundwater over a Pd-Cu catalyst supported on carbon nanotubes was investigated. It was observed that the catalyst performance was affected by the groundwater composition. The nitrate conversion attained was higher in the experiment using only deionized water as solvent than in the case of simulated or real groundwater. With exception of sulphate ions, all the other solutes evaluated (chloride and phosphate ions and natural organic matter) had a negative influence on the catalytic activity and selectivity to nitrogen.

Understanding the Adsorption Interface of Polyelectrolyte Coating on Redox Active Nanoparticles Using Soft Particle Electrokinetics and Its Biological Activity

PubMed Central

2015-01-01

The application of cerium oxide nanoparticles (CNPs) for therapeutic purposes requires a stable dispersion of nanoparticles in a biological environment. The objective of this study is to tailor the properties of polyelectrolyte coated CNPs as a function of molecular weight to achieve a stable and catalytic active dispersion. The coating of CNPs with polyacrylic acid (PAA) has increased the dispersion stability of CNPs and enhanced the catalytic ability. The stability of PAA coating was analyzed using the change in the Gibbs free energy computed by the Langmuir adsorption model. The adsorption isotherms were determined using soft particle electrokinetics which overcomes the challenges presented by other techniques. The change in Gibbs free energy was highest for CNPs coated with PAA of 250 kg/mol indicating the most stable coating. The change in free energy for PAA of 100 kg/mol coated CNPs was 85% lower than the PAA of 250 kg/mol coated CNPs. This significant difference is caused by the strong adsorption of PAA of 100 kg/mol on CNPs. Catalytic activity of PAA-CNPs is assessed by the catalase enzymatic mimetic activity of nanoparticles. The catalase activity was higher for PAA coated CNPs as compared to bare CNPs which indicated preferential adsorption of hydrogen peroxide induced by coating. This indicates that the catalase activity is also affected by the structure of the coating layer. PMID:24673655

Catalyst material and method of making

DOEpatents

Matson, Dean W.; Fulton, John L.; Linehan, John C.; Bean, Roger M.; Brewer, Thomas D.; Werpy, Todd A.; Darab, John G.

1997-01-01

The material of the present invention is a mixture of catalytically active material and carrier materials, which may be catalytically active themselves. Hence, the material of the present invention provides a catalyst particle that has catalytically active material throughout its bulk volume as well as on its surface. The presence of the catalytically active material throughout the bulk volume is achieved by chemical combination of catalytically active materials with carrier materials prior to or simultaneously with crystallite formation.

Catalyst material and method of making

DOEpatents

Matson, D.W.; Fulton, J.L.; Linehan, J.C.; Bean, R.M.; Brewer, T.D.; Werpy, T.A.; Darab, J.G.

1997-07-29

The material of the present invention is a mixture of catalytically active material and carrier materials, which may be catalytically active themselves. Hence, the material of the present invention provides a catalyst particle that has catalytically active material throughout its bulk volume as well as on its surface. The presence of the catalytically active material throughout the bulk volume is achieved by chemical combination of catalytically active materials with carrier materials prior to or simultaneously with crystallite formation. 7 figs.

Analysis of the mechanism of activation of cAMP-dependent protein kinase through the study of mutants of the yeast regulatory subunit.

PubMed

Zaremberg, V; Moreno, S

1996-04-01

Spontaneous mutations in the gene which encodes the regulatory subunit of cAMP-dependent protein kinase (PKA) of Saccharomyces cerevisiae (BCY1) have been isolated previously [Cannon, J. F., Gibbs, J. B. & Tatchell, K. (1986) Genetics 113, 247-264] by selection of ras2::LEU2 revertants that grew on non-fermentable carbon sources. The revertants were placed into groups of increasing severity based on the number of PKA-dependent traits affected [Cannon, J. F., Gitan, R. & Tatchell, K. (1990) J. Biol. Chem. 265, 11897-11904]. In this work the ras2 mutation has been crossed out in each bcy1 allele and the phenotypes of these mutants have been assessed. The order of severity of the mutants in both genetic backgrounds is maintained but the severity of each mutant in the normal background is higher than in the ras2::LEU2 background. Total catalytic-subunit and regulatory-subunit activities were measured in crude extracts of the bcy1 ras2::LEU2 mutants. With one exception (bcy1-6) the calculated regulatory subunit/catalytic subunit ratios of the bcy1 mutants relative to that of wild-type cells were greater than one. The dependence of PKA activity on cAMP was measured in permeabilized cells. The strains show an activity ratio in the absence and presence of cAMP in the range 0.5-1 for Kemptide phosphorylation. Overexpression of the high-affinity cAMP phosphodiesterase gene (PDE2) in the bcy1 ras2::LEU2 strains did not alter their PKA-dependent phenotypes. However, transformants were not observed from the parental ras2::LEU2 strain and the bcy1-6 ras2::LEU2 strain. The results are discussed with respect to a hypothesis for the molecular mechanism of the differential reversal of ras2 phenotypes by the bcy1 alleles. Mutations in the regulatory subunit are predicted to affect the structure of the holoenzyme such that the catalytic subunit is capable of maintaining an active catalytic state, without the need to dissociate from the regulatory subunit.

pH-Dependent Binding of Chloride to a Marine Alkaline Phosphatase Affects the Catalysis, Active Site Stability, and Dimer Equilibrium.

PubMed

Hjörleifsson, Jens G; Ásgeirsson, Bjarni

2017-09-26

The effect of ionic strength on enzyme activity and stability varies considerably between enzymes. Ionic strength is known to affect the catalytic activity of some alkaline phosphatases (APs), such as Escherichia coli AP, but how ions affect APs is debated. Here, we studied the effect of various ions on a cold-adapted AP from Vibrio splendidus (VAP). Previously, we have found that the active form of VAP is extremely unstable at low ionic strengths. Here we show that NaCl increased the activity and stability of VAP and that the effect was pH-dependent in the range of pH 7-10. The activity profile as a function of pH formed two maxima, indicating a possible conformational change. Bringing the pH from the neutral to the alkaline range was accompanied by a large increase in both the K i for inorganic phosphate (product inhibition) and the K M for p-nitrophenyl phosphate. The activity transitions observed as the pH was varied correlated with structural changes as monitored by tryptophan fluorescence. Thermal and urea-induced inactivation was shown to be accompanied by neither dissociation of the active site metal ions nor dimer dissociation. This would suggest that the inactivation involved subtle changes in active site conformation. Furthermore, the VAP dimer equilibrium was studied for the first time and shown to highly favor dimerization, which was dependent on pH and NaCl concentration. Taken together, the data support a model in which anions bind to some specific acceptor in the active site of VAP, resulting in great stabilization and catalytic rate enhancement, presumably through a different mechanism.

The amyloid architecture provides a scaffold for enzyme-like catalysts.

PubMed

Al-Garawi, Z S; McIntosh, B A; Neill-Hall, D; Hatimy, A A; Sweet, S M; Bagley, M C; Serpell, L C

2017-08-03

Natural biological enzymes possess catalytic sites that are generally surrounded by a large three-dimensional scaffold. However, the proportion of the protein molecule that participates in the catalytic reaction is relatively small. The generation of artificial or miniature enzymes has long been a focus of research because enzyme mimetics can be produced with high activity at low cost. These enzymes aim to mimic the active sites without the additional architecture contributed by the protein chain. Previous work has shown that amyloidogenic peptides are able to self-assemble to create an active site that is capable of binding zinc and catalysing an esterase reaction. Here, we describe the structural characterisation of a set of designed peptides that form an amyloid-like architecture and reveal that their capability to mimic carbonic anhydrase and serve as enzyme-like catalysts is related to their ability to self-assemble. These amyloid fibril structures can bind the metal ion Zn 2+ via a three-dimensional arrangement of His residues created by the amyloid architecture. Our results suggest that the catalytic efficiency of amyloid-like assembly is not only zinc-dependent but also depends on an active centre created by the peptides which is, in turn, dependent on the ordered architecture. These fibrils have good esterase activity, and they may serve as good models for the evolution of modern-day enzymes. Furthermore, they may be useful in designing self-assembling fibrils for applications as metal ion catalysts. This study also demonstrates that the ligands surrounding the catalytic site affect the affinity of the zinc-binding site to bind the substrate contributing to the enzymatic activity of the assembled peptides.

Catalytic bioreactors and methods of using same

DOEpatents

Worden, Robert Mark; Liu, Yangmu Chloe

2017-07-25

Various embodiments provide a bioreactor for producing a bioproduct comprising one or more catalytically active zones located in a housing and adapted to keep two incompatible gaseous reactants separated when in a gas phase, wherein each of the one or more catalytically active zones may comprise a catalytic component retainer and a catalytic component retained within and/or thereon. Each of the catalytically active zones may additionally or alternatively comprise a liquid medium located on either side of the catalytic component retainer. Catalytic component may include a microbial cell culture located within and/or on the catalytic component retainer, a suspended catalytic component suspended in the liquid medium, or a combination thereof. Methods of using various embodiments of the bioreactor to produce a bioproduct, such as isobutanol, are also provided.

Chemistry and catalysis of coal liquefaction catalytic and thermal upgrading of coal liquid and hydrogenation of CO to produce fuels. Quarterly progress report, July-September 1980

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiser, W.H.

1981-02-01

Studies on the basic properties of supported sulfide catalysts showed that different supports have a profound influence on catalytic activities of CoMo catalysts. The three functions of hydrodesulfurization, hydrogenation and cracking were differently affected depending on the support used and the manner of preparation of the catalyst. Also, incorporation of additives to the support showed that the different catalytic functions can be selectively affected. A systematic study concerned with catalytic cracking of coal-derived liquids, viz., an SRC-II middle-heavy distillate and four hydrotreated SRC-II products was carried out in the range of 375 to 500/sup 0/C (LHSV, 0.2 to 3.9 h/supmore » -1/). Hydrotreatment, even to a limited extent, results in a remarkable improvement in the yield of gasoline-range products from the SRC-II distillate. This improvement is ascribed to: (a) hydrogenolysis reactions leading to lower molecular weight feedstock components and (b) limited hydrogenation of aromatic rings leading to polycyclic feed components with sufficient concentration of hydroaromatic rings needed for effective cracking. The results with model compounds and the data on hydrogen consumption during hydrotreatment of SRC-II liquids indicate that for tricyclic, tetracyclic, and pentacyclic coal-liquid components the optimal concentration of hydroaromatic rings for effective subsequent cracking is at least two rings per molecule.« less

Stability, surface features, and atom leaching of palladium nanoparticles: toward prediction of catalytic functionality.

PubMed

Ramezani-Dakhel, Hadi; Mirau, Peter A; Naik, Rajesh R; Knecht, Marc R; Heinz, Hendrik

2013-04-21

Surfactant-stabilized metal nanoparticles have shown promise as catalysts although specific surface features and their influence on catalytic performance have not been well understood. We quantify the thermodynamic stability, the facet composition of the surface, and distinct atom types that affect rates of atom leaching for a series of twenty near-spherical Pd nanoparticles of 1.8 to 3.1 nm size using computational models. Cohesive energies indicate higher stability of certain particles that feature an approximate 60/20/20 ratio of {111}, {100}, and {110} facets while less stable particles exhibit widely variable facet composition. Unique patterns of atom types on the surface cause apparent differences in binding energies and changes in reactivity. Estimates of the relative rate of atom leaching as a function of particle size were obtained by the summation of Boltzmann-weighted binding energies over all surface atoms. Computed leaching rates are in good qualitative correlation with the measured catalytic activity of peptide-stabilized Pd nanoparticles of the same shape and size in Stille coupling reactions. The agreement supports rate-controlling contributions by atom leaching in the presence of reactive substrates. The computational approach provides a pathway to estimate the catalytic activity of metal nanostructures of engineered shape and size, and possible further refinements are described.

Correlation between the microstructures of graphite oxides and their catalytic behaviors in air oxidation of benzyl alcohol.

PubMed

Geng, Longlong; Wu, Shujie; Zou, Yongcun; Jia, Mingjun; Zhang, Wenxiang; Yan, Wenfu; Liu, Gang

2014-05-01

A series of graphite oxide (GO) materials were obtained by thermal treatment of oxidized natural graphite powder at different temperatures (from 100 to 200 °C). The microstructure evolution (i.e., layer structure and surface functional groups) of the graphite oxide during the heating process is studied by various characterization means, including XRD, N2 adsorption, TG-DTA, in situ DRIFT, XPS, Raman, TEM and Boehm titration. The characterization results show that the structures of GO materials change gradually from multilayer sheets to a transparent ultrathin 2D structure of the carbon sheets. The concentration of surface COH and HOCO groups decrease significantly upon treating temperature increasing. Benzyl alcohol oxidation with air as oxidant source was carried out to detect the catalytic behaviors of different GO materials. The activities of GO materials decrease with the increase of treating temperatures. It shows that the structure properties, including ultrathin sheets and high specific surface area, are not crucial factors affecting the catalytic activity. The type and amount of surface oxygen-containing functional groups of GO materials tightly correlates with the catalytic performance. Carboxylic groups on the surface of GO should act as oxidative sites for benzyl alcohol and the reduced form could be reoxidized by molecular oxygen. Copyright © 2014 Elsevier Inc. All rights reserved.

Ionizable side chains at catalytic active sites of enzymes.

PubMed

Jimenez-Morales, David; Liang, Jie; Eisenberg, Bob

2012-05-01

Catalytic active sites of enzymes of known structure can be well defined by a modern program of computational geometry. The CASTp program was used to define and measure the volume of the catalytic active sites of 573 enzymes in the Catalytic Site Atlas database. The active sites are identified as catalytic because the amino acids they contain are known to participate in the chemical reaction catalyzed by the enzyme. Acid and base side chains are reliable markers of catalytic active sites. The catalytic active sites have 4 acid and 5 base side chains, in an average volume of 1,072 Å(3). The number density of acid side chains is 8.3 M (in chemical units); the number density of basic side chains is 10.6 M. The catalytic active site of these enzymes is an unusual electrostatic and steric environment in which side chains and reactants are crowded together in a mixture more like an ionic liquid than an ideal infinitely dilute solution. The electrostatics and crowding of reactants and side chains seems likely to be important for catalytic function. In three types of analogous ion channels, simulation of crowded charges accounts for the main properties of selectivity measured in a wide range of solutions and concentrations. It seems wise to use mathematics designed to study interacting complex fluids when making models of the catalytic active sites of enzymes.

Ionizable Side Chains at Catalytic Active Sites of Enzymes

PubMed Central

Jimenez-Morales, David; Liang, Jie

2012-01-01

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

Catalytic activity of bimetallic Zn/TiO2 catalyst for degradation of herbicide paraquat: synthesis and characterization

NASA Astrophysics Data System (ADS)

Sakee, Uthai; Wanchanthuek, Ratchaneekorn

2017-11-01

The preparation and characterization of Zn/TiO2 catalysts were performed and the photocatalytic properties of the resulting catalysts were tested using the paraquat degradation reaction under UV and solar light irradiation. The effect of the preparation method, amount of Zn loading, the calcination temperature and the thermal annealing during the autoclave aging were studied as well as the light irradiation during the testing reaction. The initial concentration of paraquat was 400 ppm, the pH during the catalytic testing was seven and the reaction temperature was 30 °C. The characterization information were obtained from XRD, XPS, UV-vis diffuse reflectance, FTIR, TEM and BET techniques. They were used to explain the expressed catalytic activity of Zn/TiO2. The results showed that the Zn/TiO2 catalyst from the hydrothermal method could remove about 80% of the paraquat from the solution (using 4 g l-1 of catalyst). The characterization data showed that the surface area, porous structure and dispersion of Zn species could affect the ability of the paraquat removal rather than the crystallnity of the TiO2 in the catalyst. The XPS spectra suggested that the preparation method, between the sol gel and hydrothermal, could not affect the state of the Zn and Ti, which presented in the Zn2+ and Ti4+ forms. This primary result will lead us to further study to elucidate the main active site by the XPS technique. Moreover, it clearly showed that the lowering of the band gap energy in the Zn/TiO2 was achieved (compared to bare TiO2), and this phenomena was one of the factors that gave the higher photocatalytic activity of the Zn/TiO2 catalyst.

The role of T56 in controlling the flexibility of the distal histidine in dehaloperoxidase-hemoglobin from Amphitrite ornata.

PubMed

Jiang, Shu; Wright, Iain; Swartz, Paul; Franzen, Stefan

2013-10-01

The activation of dehaloperoxidase-hemoglobin (DHP) to form a ferryl intermediate requires the distal histidine, H55, to act as an acid base catalyst. The lack of ancillary amino acids in the distal pocket to assist in this process makes H55 even more important to the formation of active intermediates than in conventional peroxidases. Therefore, one can infer that the precise conformation H55 may greatly affect the enzymatic activity. Using site-direct mutagenesis at position T56, immediately adjacent to H55, we have confirmed that subtle changes in the conformation of H55 affect the catalytic efficiency of DHP. Mutating T56 to a smaller amino acid appears to permit H55 to rotate with relatively low barriers between conformations in the distal pocket, which may lead to an increase in catalytic activity. On the other hand, larger amino acids in the neighboring site appear to restrict the rotation of H55 due to the steric hindrance. In the case of T56V, which is an isosteric mutation, H55 appears less mobile, but forced to be closer to the heme iron than in wild type. Both proximity to the heme iron and flexibility of motion in some of the mutants can result in an increased catalytic rate, but can also lead to protein inactivation due to ligation of H55 to the heme iron, which is known as hemichrome formation. A balance of enzymatic rate and protein stability with respect to hemichrome formation appears to be optimum in wild type DHP (WT-DHP). Copyright © 2013 Elsevier B.V. All rights reserved.

Formation of RNA oligomers on montmorillonite: site of catalysis

NASA Technical Reports Server (NTRS)

Ertem, G.; Ferris, J. P.

1998-01-01

Certain montmorillonites catalyze the self condensation of the 5'-phosphorimidazolide of nucleosides in pH 8 aqueous electrolyte solutions at ambient temperatures leading to formation of RNA oligomers. In order to establish the nature of the sites on montmorillonite responsible for this catalytic activity, oligomerization reactions were run with montmorillonites which had been selectively modified (I) at the edges by (a) fluoride treatment, (b) silylation, (c) metaphosphate treatment of the anion exchange sites (II) in the interlayer by (a) saturation with quaternary alkylammonium ions of increasing size, (b) aluminum polyoxo cations. High pressure liquid chromatography, HPLC, analysis of condensation products for their chain lengths and yields indicated that modification at the edges did not affect the catalytic activity to a significant extent, while blocking the interlayer strongly inhibited product formation.

Synthesis and characterization of supported polysugar-stabilized palladium nanoparticle catalysts for enhanced hydrodechlorination of trichloroethylene

NASA Astrophysics Data System (ADS)

Bacik, Deborah B.; Zhang, Man; Zhao, Dongye; Roberts, Christopher B.; Seehra, Mohinar S.; Singh, Vivek; Shah, Naresh

2012-07-01

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al2O3 support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.

Origins of the temperature dependence of hammerhead ribozyme catalysis.

PubMed Central

Peracchi, A

1999-01-01

The difficulties in interpreting the temperature dependence of protein enzyme reactions are well recognized. Here, the hammerhead ribozyme cleavage was investigated under single-turnover conditions between 0 and 60 degrees C as a model for RNA-catalyzed reactions. Under the adopted conditions, the chemical step appears to be rate-limiting. However, the observed rate of cleavage is affected by pre-catalytic equilibria involving deprotonation of an essential group and binding of at least one low-affinity Mg2+ion. Thus, the apparent entropy and enthalpy of activation include contributions from the temperature dependence of these equilibria, precluding a simple physical interpretation of the observed activation parameters. Similar pre-catalytic equilibria likely contribute to the observed activation parameters for ribozyme reactions in general. The Arrhenius plot for the hammerhead reaction is substantially curved over the temperature range considered, which suggests the occurrence of a conformational change of the ribozyme ground state around physiological temperatures. PMID:10390528

Switchable Hydrolase Based on Reversible Formation of Supramolecular Catalytic Site Using a Self-Assembling Peptide.

PubMed

Zhang, Chunqiu; Shafi, Ramim; Lampel, Ayala; MacPherson, Douglas; Pappas, Charalampos G; Narang, Vishal; Wang, Tong; Maldarelli, Charles; Ulijn, Rein V

2017-11-13

The reversible regulation of catalytic activity is a feature found in natural enzymes which is not commonly observed in artificial catalytic systems. Here, we fabricate an artificial hydrolase with pH-switchable activity, achieved by introducing a catalytic histidine residue at the terminus of a pH-responsive peptide. The peptide exhibits a conformational transition from random coil to β-sheet by changing the pH from acidic to alkaline. The β-sheet self-assembles to form long fibrils with the hydrophobic edge and histidine residues extending in an ordered array as the catalytic microenvironment, which shows significant esterase activity. Catalytic activity can be reversible switched by pH-induced assembly/disassembly of the fibrils into random coils. At higher concentrations, the peptide forms a hydrogel which is also catalytically active and maintains its reversible (de-)activation. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Molecular mechanisms of isocitrate dehydrogenase 1 (IDH1) mutations identified in tumors: The role of size and hydrophobicity at residue 132 on catalytic efficiency

PubMed Central

Avellaneda Matteo, Diego; Grunseth, Adam J.; Gonzalez, Eric R.; Anselmo, Stacy L.; Kennedy, Madison A.; Moman, Precious; Scott, David A.; Hoang, An; Sohl, Christal D.

2017-01-01

Isocitrate dehydrogenase 1 (IDH1) catalyzes the reversible NADP+-dependent conversion of isocitrate (ICT) to α-ketoglutarate (αKG) in the cytosol and peroxisomes. Mutations in IDH1 have been implicated in >80% of lower grade gliomas and secondary glioblastomas and primarily affect residue 132, which helps coordinate substrate binding. However, other mutations found in the active site have also been identified in tumors. IDH1 mutations typically result in a loss of catalytic activity, but many also can catalyze a new reaction, the NADPH-dependent reduction of αKG to d-2-hydroxyglutarate (D2HG). D2HG is a proposed oncometabolite that can competitively inhibit αKG-dependent enzymes. Some kinetic parameters have been reported for several IDH1 mutations, and there is evidence that mutant IDH1 enzymes vary widely in their ability to produce D2HG. We report that most IDH1 mutations identified in tumors are severely deficient in catalyzing the normal oxidation reaction, but that D2HG production efficiency varies among mutant enzymes up to ∼640-fold. Common IDH1 mutations have moderate catalytic efficiencies for D2HG production, whereas rarer mutations exhibit either very low or very high efficiencies. We then designed a series of experimental IDH1 mutants to understand the features that support D2HG production. We show that this new catalytic activity observed in tumors is supported by mutations at residue 132 that have a smaller van der Waals volume and are more hydrophobic. We report that one mutation can support both the normal and neomorphic reactions. These studies illuminate catalytic features of mutations found in the majority of patients with lower grade gliomas. PMID:28330869

Fast decolorization of azo methyl orange via heterogeneous Fenton and Fenton-like reactions using alginate-Fe2+/Fe3+ films as catalysts.

PubMed

Quadrado, Rafael F N; Fajardo, André R

2017-12-01

The efficiency of Fenton and Fenton-like processes can be seriously affected by the continuous loss of iron ions and by the formation of solid sludge. Here, alginate (Alg) films were synthesized to stabilize iron ions (Fe 2+ and Fe 3+ ) and to enhance their catalytic activities towards the decolorization of methyl orange via heterogeneous Fenton and Fenton-like processes. Iron ions were ionically bond to the Alg molecules resulting in a three-dimensional network with specific structural and morphological features according to the valence states of iron. Our results demonstrated that both Alg-Fe 2+ and Alg-Fe 3+ films show highlighted catalytic activity for the decolorization of MO and high decolorization rates. Reuse experiments demonstrated that both films could be employed in at least five consecutive decolorization processes without losing their catalytic efficiency or stability. Taken together, our findings reveal that the Alg-Fe 2+ and Alg-Fe 3+ films may be suitable low-cost catalysts in heterogeneous Fenton and Fenton-like processes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Graphene oxide nanoplatforms to enhance catalytic performance of iron phthalocyanine for oxygen reduction reaction in bioelectrochemical systems

NASA Astrophysics Data System (ADS)

Costa de Oliveira, Maida Aysla; Mecheri, Barbara; D'Epifanio, Alessandra; Placidi, Ernesto; Arciprete, Fabrizio; Valentini, Federica; Perandini, Alessando; Valentini, Veronica; Licoccia, Silvia

2017-07-01

We report the development of electrocatalysts based on iron phthalocyanine (FePc) supported on graphene oxide (GO), obtained by electrochemical oxidation of graphite in aqueous solution of LiCl, LiClO4, and NaClO4. Structure, surface chemistry, morphology, and thermal stability of the prepared materials were investigated by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, atomic force microscopy (AFM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The catalytic activity toward oxygen reduction reaction (ORR) at neutral pH was evaluated by cyclic voltammetry. The experimental results demonstrate that the oxidation degree of GO supports affects the overall catalytic activity of FePc/GO, due to a modulation effect of the interaction between FePc and the basal plane of GO. On the basis of electrochemical, spectroscopic, and morphological investigations, FePc/GO_LiCl was selected to be assembled at the cathode side of a microbial fuel cell prototype, demonstrating a good electrochemical performance in terms of voltage and power generation.

Tailoring the Hydrothermal Synthesis of Stainless Steel Wire Sieve-Supported Ag-Doped ZnO Nanowires to Optimize Their Photo-catalytic Activity

NASA Astrophysics Data System (ADS)

Jing, W. X.; Shi, J. F.; Xu, Z. P.; Jiang, Z. D.; Wei, Z. Y.; Zhou, F.; Wu, Q.; Cui, Q. B.

2018-03-01

Batches of un-doped and Ag-doped ZnO nanowires (ZnONWs) were prepared hydrothermally on stainless steel wire sieves at varied Zn2+ concentrations of the growth solution and at different Ag+ concentrations of the silver nitrate solution. Methylene blue solution was degraded with these as-prepared ZnONWs in the presences of ultraviolet irradiation. It is found that both the processing parameters greatly affect the surface textures, wettability, and photo-activity of the ZnONWs. The latter synthesizing parameter is optimized only after the former one has been finely regulated. The un-doped and Ag-doped ZnONWs at Zn2+ concentration of 75 mM of the growth solution and at Ag+ concentration of3 mM of the silver nitrate solution both produce Gaussian rough surfaces and in each batch are most hydrophilic. Therefore, in the related batch the contacting surface area of the catalyst is the largest, the hydroxyl radicals attached on the top ends of corresponding ZnONWs the most, and the catalytic activity of these catalysts the optimal. Besides these, the latter synthesizing parameter affects the photo-activity of Ag-doped ZnONWs more significantly than the former one does that of un-doped ZnONWs.

Computational Investigation of the pH Dependence of Loop Flexibility and Catalytic Function in Glycoside Hydrolases*

PubMed Central

Bu, Lintao; Crowley, Michael F.; Himmel, Michael E.; Beckham, Gregg T.

2013-01-01

Cellulase enzymes cleave glycosidic bonds in cellulose to produce cellobiose via either retaining or inverting hydrolysis mechanisms, which are significantly pH-dependent. Many fungal cellulases function optimally at pH ∼5, and their activities decrease dramatically at higher or lower pH. To understand the molecular-level implications of pH in cellulase structure, we use a hybrid, solvent-based, constant pH molecular dynamics method combined with pH-based replica exchange to determine the pKa values of titratable residues of a glycoside hydrolase (GH) family 6 cellobiohydrolase (Cel6A) and a GH family 7 cellobiohydrolase (Cel7A) from the fungus Hypocrea jecorina. For both enzymes, we demonstrate that a bound substrate significantly affects the pKa values of the acid residues at the catalytic center. The calculated pKa values of catalytic residues confirm their proposed roles from structural studies and are consistent with the experimentally measured apparent pKa values. Additionally, GHs are known to impart a strained pucker conformation in carbohydrate substrates in active sites for catalysis, and results from free energy calculations combined with constant pH molecular dynamics suggest that the correct ring pucker is stable near the optimal pH for both Cel6A and Cel7A. Much longer molecular dynamics simulations of Cel6A and Cel7A with fixed protonation states based on the calculated pKa values suggest that pH affects the flexibility of tunnel loops, which likely affects processivity and substrate complexation. Taken together, this work demonstrates several molecular-level effects of pH on GH enzymes important for cellulose turnover in the biosphere and relevant to biomass conversion processes. PMID:23504310

Decomposition of energetic molecules by interfacing with a catalytic oxide: opportunities and challenges

NASA Astrophysics Data System (ADS)

Wang, Fenggong; Tsyshevsky, Roman; Zverev, Anton; Mitrofanov, Anatoly; Kuklja, Maija

Organic-inorganic interfaces provide both intrigues and opportunities for designing systems that possess properties and functionalities inaccessible by each individual component. In particular, mixing with a photocatalyst may significantly affect the adsorption, decomposition, and photoresponse of organic molecules. Here, we choose the formulation of TiO2 and trinitrotoluene (TNT), a highly catalytic oxide and a prominent explosive, as a prototypical example to explore the interaction at the interface on the photosensitivity of energetic materials. We show that, whether or not a catalytic oxide additive can help molecular decompositions under light illumination depends largely on the band alignment between the oxide surface and the energetic molecule. Furthermore, an oxygen vacancy can lead to the electron density transfer from the surface to the energetic molecules, causing an enhancement of the bonding between molecules and surface and a reduction of the molecular decomposition activation barriers.

Role of minerals in the thermal alteration of organic matter. I - Generation of gases and condensates under dry condition

NASA Technical Reports Server (NTRS)

Tannenbaum, E.; Kaplan, I. R.

1985-01-01

Pyrolysis experiments conducted at 200 and 300 C on kerogen and bitumen from the Monterey formation and on the Green River Formation kerogen with montmorillonite, illite, and calcite added are described. The pyrolysis products are identified and gas and condensate analyses are performed. A catalytic effect is detected in the pyrolysis of kerogen with montmorillonite; however, illite and calcite display no catalytic activity. The increased production of C1-C6 hydrocarbons and the dominance of branched hydrocarbons in the C4-C6 range reveals a catalytic influence. It is observed that the catalysis of montmorillonite is greater during bitumen pyrolysis than for kerogen, and catalysis with minerals affects the production of CO2. It is concluded that a mineral matrix is important in determining the type and amount of gases and condensates forming from organic matter under thermal stress.

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 catalytic combustion of toluene.

Triosephosphate isomerase I170V alters catalytic site, enhances stability and induces pathology in a Drosophila model of TPI deficiency

DOE PAGES

Roland, Bartholomew P.; Amrich, Christopher G.; Kammerer, Charles J.; ...

2014-10-16

Triosephosphate isomerase (TPI) is a glycolytic enzyme which homodimerizes for full catalytic activity. Mutations of the TPI gene elicit a disease known as TPI Deficiency, a glycolytic enzymopathy noted for its unique severity of neurological symptoms. Evidence suggests that TPI Deficiency pathogenesis may be due to conformational changes of the protein, likely affecting dimerization and protein stability. In this report, we genetically and physically characterize a human disease-associated TPI mutation caused by an I170V substitution. Human TPI I170V elicits behavioral abnormalities in Drosophila. An examination of hTPI I170V enzyme kinetics revealed this substitution reduced catalytic turnover, while assessments of thermalmore » stability demonstrated an increase in enzyme stability. Furthermore, the crystal structure of the homodimeric I170V mutant reveals changes in the geometry of critical residues within the catalytic pocket. In the end, collectively these data reveal new observations of the structural and kinetic determinants of TPI deficiency pathology, providing new insights into disease pathogenesis.« less

Relationship between surface property and catalytic application of amorphous NiP/Hβ catalyst for n-hexane isomerization

NASA Astrophysics Data System (ADS)

Chen, Jinshe; Duan, Zunbin; Song, Zhaoyang; Zhu, Lijun; Zhou, Yulu; Xiang, Yuzhi; Xia, Daohong

2017-12-01

The amorphous NiP nanoparticles were synthesized and a novel amorphous NiP/Hβ catalyst was prepared successfully further. Due to the superior surface property of amorphous NiP/Hβ catalyst, it exhibited good catalytic application for n-hexane isomerization. The catalytic activity of amorphous NiP/Hβ catalyst was close to that of the prepared Pt/Hβ sample, and better than that of commercial catalyst and crystalline Ni2P/Hβ catalyst. What's more, the amorphous NiP/Hβ catalyst shows high resistance to different sulfur compounds and water on account of its unique surface property. The effect of loading amounts on surface property and catalytic performance was investigated, and the structure-function relationship among them was studied ulteriorly. The results demonstrate that loading amounts have effect on textural property and surface acid property, which further affect the catalytic performance. The 10 wt.% NiP/Hβ sample has appropriate pore structure and acid property with uniformly dispersed NiP nanoparticles on surface, which is helpful for providing suitable synergistic effect. The effects of reaction conditions on surface reactions and the mechanism for n-hexane isomerization were investigated further. Based on these results, the amorphous NiP/Hβ catalyst with superior surface property probably pavesa way to overcome the drawbacks of traditional noble metal catalyst, which shows good catalytic application prospects.

Water Oxidation Catalysis for NiOOH by a Metropolis Monte Carlo Algorithm.

PubMed

Hareli, Chen; Caspary Toroker, Maytal

2018-05-08

Understanding catalytic mechanisms is important for discovering better catalysts, particularly for water splitting reactions that are of great interest to the renewable energy field. One of the best performing catalysts for water oxidation is nickel oxyhydroxide (NiOOH). However, only one mechanism has been adopted so far for modeling catalysis of the active plane: β-NiOOH(01̅5). In order to understand how a second reaction mechanism affects catalysis, we perform Density Functional Theory + U (DFT+U) calculations of a second mechanism for water oxidation reaction of NiOOH. Then, we use a Metropolis Monte Carlo algorithm to calculate how many catalytic cycles are completed when two reaction mechanisms are competing. We find that within the Metropolis algorithm, the second mechanism has a higher overpotential and is therefore not active even for large applied biases.

Atomically precise cluster catalysis towards quantum controlled catalysts

PubMed Central

Watanabe, Yoshihide

2014-01-01

Catalysis of atomically precise clusters supported on a substrate is reviewed in relation to the type of reactions. The catalytic activity of supported clusters has generally been discussed in terms of electronic structure. Several lines of evidence have indicated that the electronic structure of clusters and the geometry of clusters on a support, including the accompanying cluster-support interaction, are strongly correlated with catalytic activity. The electronic states of small clusters would be easily affected by cluster–support interactions. Several studies have suggested that it is possible to tune the electronic structure through atomic control of the cluster size. It is promising to tune not only the number of cluster atoms, but also the hybridization between the electronic states of the adsorbed reactant molecules and clusters in order to realize a quantum-controlled catalyst. PMID:27877723

Enhancing the photocatalytic degradation of Fe-Ti over SiO2 nanocomposite material for paraquat removal

NASA Astrophysics Data System (ADS)

Kruanetr, Senee; Wanchanthuek, Ratchaneekorn

2018-05-01

The effect of Fe and Ti loaded over SiO2 (called FeTi/SiO2) in paraquat degradation was studied for both the catalytic activity and the catalyst surface properties. Sufficient characterization techniques were used to obtain the physical and chemical properties of the FeTi/SiO2 system, such as the adsorption-desorption isotherm, surface area and porous structure, XRD diffraction, FTIR spectroscopy, UV–vis diffuse reflection spectrometry and XPS spectroscopy. The catalytic activity in paraquat degradation studies showed that the bimetallic Fe-Ti over SiO2 had higher activity than the monometallic of either Fe or Ti over SiO2 and also the order of the Fe and Ti loading was the significant parameter affecting the activity. The XPS showed that the level of Fe3+ over the catalyst was related to the obtained activity. Moreover, the optimum Fe:Ti ratio in the FeTi/SiO2 system was 1:1 (by weight). Finally, the effect of the support pretreatment (SiO2 pretreatment) was studied and showed a negative effect on the expressed activity.

Lamellar zirconium phosphates to host metals for catalytic purposes.

PubMed

Ballesteros-Plata, Daniel; Infantes-Molina, Antonia; Rodríguez-Aguado, Elena; Braos-García, Pilar; Rodríguez-Castellón, Enrique

2018-02-27

In the present study a porous lamellar zirconium phosphate heterostructure (PPH) formed from zirconium(iv) phosphate expanded with silica galleries (P/Zr molar ratio equal to 2 and (Si + Zr)/P equal to 3) was prepared to host noble metals. Textural and structural characterization of PPH-noble metal materials was carried out in order to elucidate the location and dispersion of the metallic particles and the properties of the resulting material to be used in catalytic processes. In the present paper, their activity in the catalytic hydrodeoxygenation (HDO) reaction of dibenzofuran (DBF) was evaluated. X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) evidenced that the structure of the pillared zirconium phosphate material was not modified by the incorporation of Pt and Pd. Moreover, transmission electron microscopy (TEM) showed a different dispersion of the noble metal. The acidity of the resulting PPH-noble metal materials also changed, although in all cases the acidity was of weak nature, and the incorporation of noble metals affected Brønsted acid sites as observed from 31 P NMR spectra. In general, the textural, structural and acidic properties of the resulting materials suggest that PPH can be considered a good candidate to be used as a catalytic support. Thus, the catalytic results of the PPH-noble metal samples indicated that the Pd sample showed a stable behavior probably ascribed to a high dispersion of the active phase. However, the Pt sample suffered from fast deactivation. The selectivity to the reaction products was strongly dependent on the noble metal employed.

Size control and catalytic activity of bio-supported palladium nanoparticles.

PubMed

Søbjerg, Lina Sveidal; Lindhardt, Anders T; Skrydstrup, Troels; Finster, Kai; Meyer, Rikke Louise

2011-07-01

The development of nanoparticles has greatly improved the catalytic properties of metals due to the higher surface to volume ratio of smaller particles. The production of nanoparticles is most commonly based on abiotic processes, but in the search for alternative protocols, bacterial cells have been identified as excellent scaffolds of nanoparticle nucleation, and bacteria have been successfully employed to recover and regenerate platinum group metals from industrial waste. We report on the formation of bio-supported palladium (Pd) nanoparticles on the surface of two bacterial species with distinctly different surfaces: the gram positive Staphylococcus sciuri and the gram negative Cupriavidus necator. We investigated how the type of bacterium and the amount of biomass affected the size and catalytic properties of the nanoparticles formed. By increasing the biomass:Pd ratio, we could produce bio-supported Pd nanoparticles smaller than 10nm in diameter, whereas lower biomass:Pd ratios resulted in particles ranging from few to hundreds of nm. The bio-supported Pd nanoparticle catalytic properties were investigated towards the Suzuki-Miyaura cross coupling reaction and hydrogenation reactions. Surprisingly, the smallest nanoparticles obtained at the highest biomass:Pd ratio showed no reactivity towards the test reactions. The lack of reactivity appears to be caused by thiol groups, which poison the catalyst by binding strongly to Pd. Different treatments intended to liberate particles from the biomass, such as burning or rinsing in acetone, did not re-establish their catalytic activity. Sulphur-free biomaterials should therefore be explored as more suitable scaffolds for Pd(0) nanoparticle formation. Copyright © 2011 Elsevier B.V. All rights reserved.

Regulation of Catalytic and Non-catalytic Functions of the Drosophila Ste20 Kinase Slik by Activation Segment Phosphorylation.

PubMed

Panneton, Vincent; Nath, Apurba; Sader, Fadi; Delaunay, Nathalie; Pelletier, Ariane; Maier, Dominic; Oh, Karen; Hipfner, David R

2015-08-21

Protein kinases carry out important functions in cells both by phosphorylating substrates and by means of regulated non-catalytic activities. Such non-catalytic functions have been ascribed to many kinases, including some members of the Ste20 family. The Drosophila Ste20 kinase Slik phosphorylates and activates Moesin in developing epithelial tissues to promote epithelial tissue integrity. It also functions non-catalytically to promote epithelial cell proliferation and tissue growth. We carried out a structure-function analysis to determine how these two distinct activities of Slik are controlled. We find that the conserved C-terminal coiled-coil domain of Slik, which is necessary and sufficient for apical localization of the kinase in epithelial cells, is not required for Moesin phosphorylation but is critical for the growth-promoting function of Slik. Slik is auto- and trans-phosphorylated in vivo. Phosphorylation of at least two of three conserved sites in the activation segment is required for both efficient catalytic activity and non-catalytic signaling. Slik function is thus dependent upon proper localization of the kinase via the C-terminal coiled-coil domain and activation via activation segment phosphorylation, which enhances both phosphorylation of substrates like Moesin and engagement of effectors of its non-catalytic growth-promoting activity. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

Analysis of in vitro evolution reveals the underlying distribution of catalytic activity among random sequences.

PubMed

Pressman, Abe; Moretti, Janina E; Campbell, Gregory W; Müller, Ulrich F; Chen, Irene A

2017-08-21

The emergence of catalytic RNA is believed to have been a key event during the origin of life. Understanding how catalytic activity is distributed across random sequences is fundamental to estimating the probability that catalytic sequences would emerge. Here, we analyze the in vitro evolution of triphosphorylating ribozymes and translate their fitnesses into absolute estimates of catalytic activity for hundreds of ribozyme families. The analysis efficiently identified highly active ribozymes and estimated catalytic activity with good accuracy. The evolutionary dynamics follow Fisher's Fundamental Theorem of Natural Selection and a corollary, permitting retrospective inference of the distribution of fitness and activity in the random sequence pool for the first time. The frequency distribution of rate constants appears to be log-normal, with a surprisingly steep dropoff at higher activity, consistent with a mechanism for the emergence of activity as the product of many independent contributions. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Correlating structural dynamics and catalytic activity of AgAu nanoparticles with ultrafast spectroscopy and all-atom molecular dynamics simulations.

PubMed

Ferbonink, G F; Rodrigues, T S; Dos Santos, D P; Camargo, P H C; Albuquerque, R Q; Nome, R A

2018-05-29

In this study, we investigated hollow AgAu nanoparticles with the goal of improving our understanding of the composition-dependent catalytic activity of these nanoparticles. AgAu nanoparticles were synthesized via the galvanic replacement method with controlled size and nanoparticle compositions. We studied extinction spectra with UV-Vis spectroscopy and simulations based on Mie theory and the boundary element method, and ultrafast spectroscopy measurements to characterize decay constants and the overall energy transfer dynamics as a function of AgAu composition. Electron-phonon coupling times for each composition were obtained from pump-power dependent pump-probe transients. These spectroscopic studies showed how nanoscale surface segregation, hollow interiors and porosity affect the surface plasmon resonance wavelength and fundamental electron-phonon coupling times. Analysis of the spectroscopic data was used to correlate electron-phonon coupling times to AgAu composition, and thus to surface segregation and catalytic activity. We have performed all-atom molecular dynamics simulations of model hollow AgAu core-shell nanoparticles to characterize nanoparticle stability and equilibrium structures, besides providing atomic level views of nanoparticle surface segregation. Overall, the basic atomistic and electron-lattice dynamics of core-shell AgAu nanoparticles characterized here thus aid the mechanistic understanding and performance optimization of AgAu nanoparticle catalysts.

Structures of the Bacillus subtilis Glutamine Synthetase Dodecamer Reveal Large Intersubunit Catalytic Conformational Changes Linked to a Unique Feedback Inhibition Mechanism*

PubMed Central

Murray, David S.; Chinnam, Nagababu; Tonthat, Nam Ky; Whitfill, Travis; Wray, Lewis V.; Fisher, Susan H.; Schumacher, Maria A.

2013-01-01

Glutamine synthetase (GS), which catalyzes the production of glutamine, plays essential roles in nitrogen metabolism. There are two main bacterial GS isoenzymes, GSI-α and GSI-β. GSI-α enzymes, which have not been structurally characterized, are uniquely feedback-inhibited by Gln. To gain insight into GSI-α function, we performed biochemical and cellular studies and obtained structures for all GSI-α catalytic and regulatory states. GSI-α forms a massive 600-kDa dodecameric machine. Unlike other characterized GS, the Bacillus subtilis enzyme undergoes dramatic intersubunit conformational alterations during formation of the transition state. Remarkably, these changes are required for active site construction. Feedback inhibition arises from a hydrogen bond network between Gln, the catalytic glutamate, and the GSI-α-specific residue, Arg62, from an adjacent subunit. Notably, Arg62 must be ejected for proper active site reorganization. Consistent with these findings, an R62A mutation abrogates Gln feedback inhibition but does not affect catalysis. Thus, these data reveal a heretofore unseen restructuring of an enzyme active site that is coupled with an isoenzyme-specific regulatory mechanism. This GSI-α-specific regulatory network could be exploited for inhibitor design against Gram-positive pathogens. PMID:24158439

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2011 CFR

2011-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device...) and (d) of this section. (c) Any fluid catalytic cracking unit catalyst regenerator under paragraph (b...

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2012 CFR

2012-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device...) and (d) of this section. (c) Any fluid catalytic cracking unit catalyst regenerator under paragraph (b...

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2010 CFR

2010-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device...) and (d) of this section. (c) Any fluid catalytic cracking unit catalyst regenerator under paragraph (b...

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.

De novo missense mutations in the NAA10 gene cause severe non-syndromic developmental delay in males and females

PubMed Central

Popp, Bernt; Støve, Svein I; Endele, Sabine; Myklebust, Line M; Hoyer, Juliane; Sticht, Heinrich; Azzarello-Burri, Silvia; Rauch, Anita; Arnesen, Thomas; Reis, André

2015-01-01

Recent studies revealed the power of whole-exome sequencing to identify mutations in sporadic cases with non-syndromic intellectual disability. We now identified de novo missense variants in NAA10 in two unrelated individuals, a boy and a girl, with severe global developmental delay but without any major dysmorphism by trio whole-exome sequencing. Both de novo variants were predicted to be deleterious, and we excluded other variants in this gene. This X-linked gene encodes N-alpha-acetyltransferase 10, the catalytic subunit of the NatA complex involved in multiple cellular processes. A single hypomorphic missense variant p.(Ser37Pro) was previously associated with Ogden syndrome in eight affected males from two different families. This rare disorder is characterized by a highly recognizable phenotype, global developmental delay and results in death during infancy. In an attempt to explain the discrepant phenotype, we used in vitro N-terminal acetylation assays which suggested that the severity of the phenotype correlates with the remaining catalytic activity. The variant in the Ogden syndrome patients exhibited a lower activity than the one seen in the boy with intellectual disability, while the variant in the girl was the most severe exhibiting only residual activity in the acetylation assays used. We propose that N-terminal acetyltransferase deficiency is clinically heterogeneous with the overall catalytic activity determining the phenotypic severity. PMID:25099252

Surface Structure Dependent Electrocatalytic Activity of Co3O4 Anchored on Graphene Sheets toward Oxygen Reduction Reaction

PubMed Central

Xiao, Junwu; Kuang, Qin; Yang, Shihe; Xiao, Fei; Wang, Shuai; Guo, Lin

2013-01-01

Catalytic activity is primarily a surface phenomenon, however, little is known about Co3O4 nanocrystals in terms of the relationship between the oxygen reduction reaction (ORR) catalytic activity and surface structure, especially when dispersed on a highly conducting support to improve the electrical conductivity and so to enhance the catalytic activity. Herein, we report a controllable synthesis of Co3O4 nanorods (NR), nanocubes (NC) and nano-octahedrons (OC) with the different exposed nanocrystalline surfaces ({110}, {100}, and {111}), uniformly anchored on graphene sheets, which has allowed us to investigate the effects of the surface structure on the ORR activity. Results show that the catalytically active sites for ORR should be the surface Co2+ ions, whereas the surface Co3+ ions catalyze CO oxidation, and the catalytic ability is closely related to the density of the catalytically active sites. These results underscore the importance of morphological control in the design of highly efficient ORR catalysts. PMID:23892418

Effect of water vapor on NH3-NO/NO2 SCR performance of fresh and aged MnOx-NbOx-CeO2 catalysts.

PubMed

Chen, Lei; Si, Zhichun; Wu, Xiaodong; Weng, Duan; Wu, Zhenwei

2015-05-01

A MnOx-NbOx-CeO2 catalyst for low temperature selective catalytic reduction (SCR) of NOx with NH3 was prepared by a sol-gel method, and characterized by NH3-NO/NO2 SCR catalytic activity, NO/NH3 oxidation activity, NOx/NH3 TPD, XRD, BET, H2-TPR and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). The results indicate that the MnOx-NbOx-CeO2 catalyst shows excellent low temperature NH3-SCR activity in the temperature range of 150-300°C. Water vapor inhibits the low temperature activity of the catalyst in standard SCR due to the inhibition of NOx adsorption. As the NO2 content increases in the feed, water vapor does not affect the activity in NO2 SCR. Meanwhile, water vapor significantly enhances the N2 selectivity of the fresh and the aged catalysts due to its inhibition of the decomposition of NH4NO3 into N2O. Copyright © 2015. Published by Elsevier B.V.

Arg354 in the catalytic centre of bovine liver catalase is protected from methylglyoxal-mediated glycation.

PubMed

Scheckhuber, Christian Q

2015-12-30

In addition to controlled post-translational modifications proteins can be modified with highly reactive compounds. Usually this leads to a compromised functionality of the protein. Methylglyoxal is one of the most common agents that attack arginine residues. Methylglyoxal is also regarded as a pro-oxidant that affects cellular redox homeostasis by contributing to the formation of reactive oxygen species. Antioxidant enzymes like catalase are required to protect the cell from oxidative damage. These enzymes are also targets for methylglyoxal-mediated modification which could severely affect their catalytic activity in breaking down reactive oxygen species to less reactive or inert compounds. Here, bovine liver catalase was incubated with high levels of methylglyoxal to induce its glycation. This treatment did not lead to a pronounced reduction of enzymatic activity. Subsequently methylglyoxal-mediated arginine modifications (hydroimidazolone and dihydroxyimidazolidine) were quantitatively analysed by sensitive nano high performance liquid chromatography/electron spray ionisation/tandem mass spectrometry. Whereas several arginine residues displayed low to moderate levels of glycation (e.g., Arg93, Arg365, Arg444) Arg354 in the active centre of catalase was never found to be modified. Bovine liver catalase is able to tolerate very high levels of the modifying α-oxoaldehyde methylglyoxal so that its essential enzymatic function is not impaired.

Autographa californica multiple nucleopolyhedrovirus PK-1 is essential for nucleocapsid assembly

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Changyong, E-mail: cyliang@yzu.edu.cn; Li, Min; Dai, Xuejuan

2013-09-01

PK-1 (Ac10) is a baculovirus-encoded serine/threonine kinase and its function is unclear. Our results showed that a pk-1 knockout AcMNPV failed to produce infectious progeny, while the pk-1 repair virus could rescue this defect. qPCR analysis demonstrated that pk-1 deletion did not affect viral DNA replication. Analysis of the repaired recombinants with truncated pk-1 mutants demonstrated that the catalytic domain of protein kinases of PK-1 was essential to viral infectivity. Moreover, those PK-1 mutants that could rescue the infectious BV production defect exhibited kinase activity in vitro. Therefore, it is suggested that the kinase activity of PK-1 is essential inmore » regulating viral propagation. Electron microscopy revealed that pk-1 deletion affected the formation of normal nucleocapsids. Masses of electron-lucent tubular structures were present in cell transfected with pk-1 knockout bacmid. Therefore, PK-1 appears to phosphorylate some viral or cellular proteins that are essential for DNA packaging to regulate nucleocapsid assembly. - Highlights: • A pk-1 knockout AcMNPV failed to produce infectious progeny. • The pk-1 deletion did not affect viral DNA replication. • The catalytic domain of protein kinases (PKc) of PK-1 was essential to viral infectivity. • The kinase activity of PK-1 is essential in regulating viral propagation. • PK-1 appears to phosphorylate some viral proteins that are essential for DNA packaging to regulate nucleocapsid assembly.« less

The new insight into the structure-activity relation of Pd/CeO2-ZrO2-Nd2O3 catalysts by Raman, in situ DRIFTS and XRD Rietveld analysis.

PubMed

Yang, X; Yang, L; Lin, J; Zhou, R

2016-01-28

Pd/CeO2-ZrO2-Nd2O3 (CZN) catalysts with different CeO2/ZrO2 molar ratios were synthesized and have been characterized by multiple techniques, e.g. XRD in combination with Rietveld refinement, UV-Raman, XPS and in situ DRIFTS. The XRD pattern of CZN with CeO2/ZrO2 molar ratios ≥1/2 can be indexed satisfactorily to the fluorite structure with a space group Fm3̄m, while the XRD patterns of CZ12 only display diffraction peaks of the tetragonal phase (S.G. P42/nmc). Nd addition can effectively stabilize the cubic structure of the CZN support and increase the enrichment of defect sites on the surface, which may be related to the better catalytic activity of Pd/CZN12 catalysts compared with Pd/CZ12. The presence of moderate ZrO2 can increase the concentration of O* active species, leading to accelerate the formation of nitrate species and thus enhance the catalytic activity of NOx and HC elimination. The Pd-dispersion decreases with the increasing Zr content, leading to the decreased CO catalytic activity, especially for the aged catalysts. The change regularity of the OSC value is almost the same with the in situ dynamic operational window, demonstrating that the in situ dynamic operational window is basically affected by the OSC value.

Effect of CDP-choline on age-dependent modifications of energy- and glutamate-linked enzyme activities in synaptic and non-synaptic mitochondria from rat cerebral cortex.

PubMed

Villa, Roberto Federico; Ferrari, Federica; Gorini, Antonella

2012-12-01

The effect of aging and CDP-choline treatment (20 mg kg⁻¹ body weight i.p. for 28 days) on the maximal rates (V(max)) of representative mitochondrial enzyme activities related to Krebs' cycle (citrate synthase, α-ketoglutarate dehydrogenase, malate dehydrogenase), glutamate and related amino acid metabolism (glutamate dehydrogenase, glutamate-oxaloacetate- and glutamate-pyruvate transaminases) were evaluated in non-synaptic and intra-synaptic "light" and "heavy" mitochondria from frontal cerebral cortex of male Wistar rats aged 4, 12, 18 and 24 months. During aging, enzyme activities vary in a complex way respect to the type of mitochondria, i.e. non-synaptic and intra-synaptic. This micro-heterogeneity is an important factor, because energy-related mitochondrial enzyme catalytic properties cause metabolic modifications of physiopathological significance in cerebral tissue in vivo, also discriminating pre- and post-synaptic sites of action for drugs and affecting tissue responsiveness to noxious stimuli. Results show that CDP-choline in vivo treatment enhances cerebral energy metabolism selectively at 18 months, specifically modifying enzyme catalytic activities in non-synaptic and intra-synaptic "light" mitochondrial sub-populations. This confirms that the observed changes in enzyme catalytic activities during aging reflect the bioenergetic state at each single age and the corresponding energy requirements, further proving that in vivo drug treatment is able to interfere with the neuronal energy metabolism. Copyright © 2012. Published by Elsevier Ltd.

Protein phosphatase 2A: a highly regulated family of serine/threonine phosphatases implicated in cell growth and signalling.

PubMed Central

Janssens, V; Goris, J

2001-01-01

Protein phosphatase 2A (PP2A) comprises a family of serine/threonine phosphatases, minimally containing a well conserved catalytic subunit, the activity of which is highly regulated. Regulation is accomplished mainly by members of a family of regulatory subunits, which determine the substrate specificity, (sub)cellular localization and catalytic activity of the PP2A holoenzymes. Moreover, the catalytic subunit is subject to two types of post-translational modification, phosphorylation and methylation, which are also thought to be important regulatory devices. The regulatory ability of PTPA (PTPase activator), originally identified as a protein stimulating the phosphotyrosine phosphatase activity of PP2A, will also be discussed, alongside the other regulatory inputs. The use of specific PP2A inhibitors and molecular genetics in yeast, Drosophila and mice has revealed roles for PP2A in cell cycle regulation, cell morphology and development. PP2A also plays a prominent role in the regulation of specific signal transduction cascades, as witnessed by its presence in a number of macromolecular signalling modules, where it is often found in association with other phosphatases and kinases. Additionally, PP2A interacts with a substantial number of other cellular and viral proteins, which are PP2A substrates, target PP2A to different subcellular compartments or affect enzyme activity. Finally, the de-regulation of PP2A in some specific pathologies will be touched upon. PMID:11171037

Comparison of Multiple Molecular Dynamics Trajectories Calculated for the Drug-Resistant HIV-1 Integrase T66I/M154I Catalytic Domain

PubMed Central

Brigo, Alessandro; Lee, Keun Woo; Iurcu Mustata, Gabriela; Briggs, James M.

2005-01-01

HIV-1 integrase (IN) is an essential enzyme for the viral replication and an interesting target for the design of new pharmaceuticals for multidrug therapy of AIDS. Single and multiple mutations of IN at residues T66, S153, or M154 confer degrees of resistance to several inhibitors that prevent the enzyme from performing its normal strand transfer activity. Four different conformations of IN were chosen from a prior molecular dynamics (MD) simulation on the modeled IN T66I/M154I catalytic core domain as starting points for additional MD studies. The aim of this article is to understand the dynamic features that may play roles in the catalytic activity of the double mutant enzyme in the absence of any inhibitor. Moreover, we want to verify the influence of using different starting points on the MD trajectories and associated dynamical properties. By comparison of the trajectories obtained from these MD simulations we have demonstrated that the starting point does not affect the conformational space explored by this protein and that the time of the simulation is long enough to achieve convergence for this system. PMID:15764656

Asymmetric catalytic formation of quaternary carbons by iminium ion trapping of radicals

NASA Astrophysics Data System (ADS)

Murphy, John J.; Bastida, David; Paria, Suva; Fagnoni, Maurizio; Melchiorre, Paolo

2016-04-01

An important goal of modern organic chemistry is to develop new catalytic strategies for enantioselective carbon-carbon bond formation that can be used to generate quaternary stereogenic centres. Whereas considerable advances have been achieved by exploiting polar reactivity, radical transformations have been far less successful. This is despite the fact that open-shell intermediates are intrinsically primed for connecting structurally congested carbons, as their reactivity is only marginally affected by steric factors. Here we show how the combination of photoredox and asymmetric organic catalysis enables enantioselective radical conjugate additions to β,β-disubstituted cyclic enones to obtain quaternary carbon stereocentres with high fidelity. Critical to our success was the design of a chiral organic catalyst, containing a redox-active carbazole moiety, that drives the formation of iminium ions and the stereoselective trapping of photochemically generated carbon-centred radicals by means of an electron-relay mechanism. We demonstrate the generality of this organocatalytic radical-trapping strategy with two sets of open-shell intermediates, formed through unrelated light-triggered pathways from readily available substrates and photoredox catalysts—this method represents the application of iminium ion activation (a successful catalytic strategy for enantioselective polar chemistry) within the realm of radical reactivity.

A highly Conserved Aspartic Acid Residue of the Chitosanase from Bacillus Sp. TS Is Involved in the Substrate Binding.

PubMed

Zhou, Zhanping; Zhao, Shuangzhi; Liu, Yang; Chang, Zhengying; Ma, Yanhe; Li, Jian; Song, Jiangning

2016-11-01

The chitosanase from Bacillus sp. TS (CsnTS) is an enzyme belonging to the glycoside hydrolase family 8. The sequence of CsnTS shares 98 % identity with the chitosanase from Bacillus sp. K17. Crystallography analysis and site-direct mutagenesis of the chitosanase from Bacillus sp. K17 identified the important residues involved in the catalytic interaction and substrate binding. However, despite progress in understanding the catalytic mechanism of the chitosanase from the family GH8, the functional roles of some residues that are highly conserved throughout this family have not been fully elucidated. This study focused on one of these residues, i.e., the aspartic acid residue at position 318. We found that apart from asparagine, mutation of Asp318 resulted in significant loss of enzyme activity. In-depth investigations showed that mutation of this residue not only impaired enzymatic activity but also affected substrate binding. Taken together, our results showed that Asp318 plays an important role in CsnTS activity.

Differentiated effect of ageing on the enzymes of Krebs' cycle, electron transfer complexes and glutamate metabolism of non-synaptic and intra-synaptic mitochondria from cerebral cortex.

PubMed

Villa, R F; Gorini, A; Hoyer, S

2006-11-01

The effect of ageing on the activity of enzymes linked to Krebs' cycle, electron transfer chain and glutamate metabolism was studied in three different types of mitochondria of cerebral cortex of 1-year old and 2-year old male Wistar rats. We assessed the maximum rate (V(max)) of the mitochondrial enzyme activities in non-synaptic perikaryal mitochondria, and in two populations of intra-synaptic mitochondria. The results indicated that: (i) in normal, steady-state cerebral cortex the values of the catalytic activities of the enzymes markedly differed in the various populations of mitochondria; (ii) in intra-synaptic mitochondria, ageing affected the catalytic properties of the enzymes linked to Krebs' cycle, electron transfer chain and glutamate metabolism; (iii) these changes were more evident in intra-synaptic "heavy" than "light" mitochondria. These results indicate a different age-related vulnerability of subpopulations of mitochondria in vivo located into synapses than non-synaptic ones.

Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO 3 Perovskites

DOE PAGES

Petrie, Jonathan R.; Cooper, Valentino R.; Freeland, John W.; ...

2016-02-11

Strain is known to greatly influence low-temperature oxygen electrocatalysis on noble metal films, leading to significant enhancements in bifunctional activity essential for fuel cells and metal-air batteries. Still, its catalytic impact on transition-metal oxide thin films, such as perovskites, is not widely understood. Here, we epitaxially strain the conducting perovskite LaNiO 3 to systematically determine its influence on both the oxygen reduction and oxygen evolution reaction. Uniquely, we found that compressive strain could significantly enhance both reactions, yielding a bifunctional catalyst that surpasses the performance of noble metals such as Pt. We attribute the improved bifunctionality to strain-induced splitting ofmore » the e g orbitals, which can customize orbital asymmetry at the surface. Lastly, analogous to strain-induced shifts in the d-band center of noble metals relative to the Fermi level, such splitting can dramatically affect catalytic activity in this perovskite and other potentially more active oxides.« less

Impact of nonsynonymous mutations of factor X on the functions of factor X and anticoagulant activity of edoxaban.

PubMed

Noguchi, Kengo; Morishima, Yoshiyuki; Takahashi, Shinichi; Ishihara, Hiroaki; Shibano, Toshiro; Murata, Mitsuru

2015-03-01

Edoxaban is an oral direct factor Xa (FXa) inhibitor and its efficacy as an oral anticoagulant is less subject to drug-food and drug-drug interaction than existing vitamin K antagonists. Although this profile of edoxaban suggests it is well suited for clinical use, it is not clear whether genetic variations of factor X influence the activity of edoxaban. Our aim was to investigate a possible impact of single-nucleotide polymorphisms (SNPs) in the factor X gene on the functions of factor X and the activity of edoxaban. Two nonsynonymous SNPs within mature factor X, Ala152Thr and Gly192Arg, were selected as possible candidates that might affect the functions of FXa and the activity of edoxaban. We measured catalytic activities of wild type and mutant FXas in a chromogenic assay using S-2222 and coagulation times including prothrombin time (PT) and activated partial thrombin time (aPTT) of plasma-containing recombinant FXs in the presence and absence of edoxaban. Michaelis-Menten kinetic parameters of FXas, Km and Vmax values, PT and aPTT were not influenced by either mutation indicating these mutations do not affect the FXa catalytic and coagulation activities. The Ki values of edoxaban for the FXas and the concentrations of edoxaban required to double PT and aPTT were not different between wild type and mutated FXas indicating that both mutations have little impact on the activity of edoxaban. In conclusion, these data suggest that edoxaban has little interpatient variability stemming from SNPs in the factor X gene.

Ab initio ONIOM-molecular dynamics (MD) study on the deamination reaction by cytidine deaminase.

PubMed

Matsubara, Toshiaki; Dupuis, Michel; Aida, Misako

2007-08-23

We applied the ONIOM-molecular dynamics (MD) method to the hydrolytic deamination of cytidine by cytidine deaminase, which is an essential step of the activation process of the anticancer drug inside the human body. The direct MD simulations were performed for the realistic model of cytidine deaminase by calculating the energy and its gradient by the ab initio ONIOM method on the fly. The ONIOM-MD calculations including the thermal motion show that the neighboring amino acid residue is an important factor of the environmental effects and significantly affects not only the geometry and energy of the substrate trapped in the pocket of the active site but also the elementary step of the catalytic reaction. We successfully simulate the second half of the catalytic cycle, which has been considered to involve the rate-determining step, and reveal that the rate-determining step is the release of the NH3 molecule.

Synthesis, characterization and catalytic oxidation properties of multi-wall carbon nanotubes with a covalently attached copper(II) salen complex

NASA Astrophysics Data System (ADS)

Salavati-Niasari, Masoud; Bazarganipour, Mehdi

2009-06-01

Hydroxyl functionalized copper(II) Schiff-base, N,N'-bis(4-hydroxysalicylidene)-ethylene-1,2-diaminecopper(II), [Cu((OH) 2-salen)], has been covalently anchored on modified MWCNTs. The new modified MWCNTs ([Cu((OH) 2-salen)]-MWCNTs) have been characterized by TEM, thermal analysis, XRD, XPS, UV-vis, DRS, FT-IR spectroscopy and elemental analysis. The modified copper(II) MWCNTs solid was used to affect the catalytic oxidation of ethylbenzene with tert-butylhydroperoxide as the oxidant at 333 K. The system is truly heterogeneous (no leaching observed) and reusable (no decrease in activity) in three consecutive runs. Acetophenone was the major product though small amounts of o- and p-hydroxyacetophenones were also formed revealing that C-H bond activation takes place both at benzylic and aromatic ring carbon atoms. Ring hydroxylation was more over the "neat" complexes than over the encapsulated complexes.

A comparative theoretical study of the catalytic activities of Au2(-) and AuAg(-) dimers for CO oxidation.

PubMed

Liu, Peng; Song, Ke; Zhang, Dongju; Liu, Chengbu

2012-05-01

The detailed mechanisms of catalytic CO oxidation over Au(2)(-) and AuAg(-) dimers, which represent the simplest models for monometal Au and bimetallic Au-Ag nanoparticles, have been studied by performing density functional theory calculations. It is found that both Au(2)(-) and AuAg(-) dimers catalyze the reaction according to the similar mono-center Eley-Rideal mechanism. The catalytic reaction is of the multi-channel and multi-step characteristic, which can proceed along four possible pathways via two or three elementary steps. In AuAg(-), the Au site is more active than the Ag site, and the calculated energy barrier values for the rate-determining step of the Au-site catalytic reaction are remarkably smaller than those for both the Ag-site catalytic reaction and the Au(2)(-) catalytic reaction. The better catalytic activity of bimetallic AuAg(-) dimer is attributed to the synergistic effect between Au and Ag atom. The present results provide valuable information for understanding the higher catalytic activity of Au-Ag nanoparticles and nanoalloys for low-temperature CO oxidation than either pure metallic catalyst.

Predicting Catalytic Activity of Nanoparticles by a DFT-Aided Machine-Learning Algorithm.

PubMed

Jinnouchi, Ryosuke; Asahi, Ryoji

2017-09-07

Catalytic activities are often dominated by a few specific surface sites, and designing active sites is the key to realize high-performance heterogeneous catalysts. The great triumphs of modern surface science lead to reproduce catalytic reaction rates by modeling the arrangement of surface atoms with well-defined single-crystal surfaces. However, this method has limitations in the case for highly inhomogeneous atomic configurations such as on alloy nanoparticles with atomic-scale defects, where the arrangement cannot be decomposed into single crystals. Here, we propose a universal machine-learning scheme using a local similarity kernel, which allows interrogation of catalytic activities based on local atomic configurations. We then apply it to direct NO decomposition on RhAu alloy nanoparticles. The proposed method can efficiently predict energetics of catalytic reactions on nanoparticles using DFT data on single crystals, and its combination with kinetic analysis can provide detailed information on structures of active sites and size- and composition-dependent catalytic activities.

Racial and genetic determinants of plasma factor XIII activity.

PubMed

Saha, N; Aston, C E; Low, P S; Kamboh, M I

2000-12-01

Factor XIII (F XIII), a plasma transglutaminase, is essential for normal hemostasis and fibrinolysis. Plasma F XIII consists of two catalytic A (F XIIIA) and two non-catalytic B (F XIIIB) subunits. Activated F XIII is involved in the formation of fibrin gel by covalently crosslinking fibrin monomers. As the characteristics of the fibrin gel structure have been shown to be associated with the risk of coronary heart disease (CHD), F XIII activity may play a seminal role in its etiology. In this investigation, we determined plasma F XIII activity in two racial groups, including Asian Indians (n = 258) and Chinese (n = 385). Adjusted plasma F XIII activity was significantly higher in Indian men (142 vs. 110%; P<0.0001) and women (158 vs. 111%; P<0.0001) than their Chinese counterparts. As compared to Indians where the distribution of F XIII activity was almost normal, in Chinese it was skewed towards low activity. In both racial groups, bivariate and multivariate analyses showed strong correlation of F XIII activity with plasma fibrinogen and plasminogen levels. Race explained about 25% of the variation in F XIII activity even after the adjustment of significant correlates. We also determined the contribution of common genetic polymorphisms in the F XIIIA and F XIIIB genes in affecting plasma F XIII activity. Both loci showed significant and independent effects on plasma F XIII activity in Indians (F XIIIA, P< 0.01; F XIIIB, P<0.05) and Chinese (F XIIIA, P<0.0001; F XIIIB, P<0.13) in a gene dosage fashion. This study shows that both racial and genetic components play a significant role in determining plasma F XIII activity, and consequently it may affect the quantitative risk of CHD. Copyright 2000 Wiley-Liss, Inc.

Conversion of methanol to propylene over hierarchical HZSM-5: the effect of Al spatial distribution.

PubMed

Li, Jianwen; Ma, Hongfang; Chen, Yan; Xu, Zhiqiang; Li, Chunzhong; Ying, Weiyong

2018-06-08

Different silicon sources caused diverse Al spatial distribution in HZSM-5, and this affected the hierarchical structures and catalytic performance of desilicated zeolites. After being treated with 0.1 M NaOH, HZSM-5 zeolites synthesized with silica sol exhibited relatively widely distributed mesopores and channels, and possessed highly improved propylene selectivity and activity stability.

Catalytic Hydroamination of Alkynes and Norbornene with Neutral and Cationic Tantalum Imido Complexes

PubMed Central

Anderson, Laura L.; Arnold, John; Bergman, Robert G.

2005-01-01

Several tantalum imido complexes have been synthesized and shown to efficiently catalyze the hydroamination of internal and terminal alkynes. An unusual hydroamination/hydroarylation reaction of norbornene catalyzed by a highly electrophilic cationic tantalum imido complex is also reported. Factors affecting catalyst activity and selectivity are discussed along with mechanistic insights gained from stoichiometric reactions. PMID:15255680

Molecular Self-Assembly Strategy for Generating Catalytic Hybrid Polypeptides

PubMed Central

Ikezoe, Yasuhiro; Pike, Douglas H.; Nanda, Vikas; Matsui, Hiroshi

2016-01-01

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β-sheets and amyloid fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. The enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality. PMID:27116246

Molecular self-assembly strategy for generating catalytic hybrid polypeptides

DOE PAGES

Maeda, Yoshiaki; Fang, Justin; Ikezoe, Yasuhiro; ...

2016-04-26

Recently, catalytic peptides were introduced that mimicked protease activities and showed promising selectivity of products even in organic solvents where protease cannot perform well. However, their catalytic efficiency was extremely low compared to natural enzyme counterparts presumably due to the lack of stable tertiary fold. We hypothesized that assembling these peptides along with simple hydrophobic pockets, mimicking enzyme active sites, could enhance the catalytic activity. Here we fused the sequence of catalytic peptide CP4, capable of protease and esterase-like activities, into a short amyloidogenic peptide fragment of Aβ. When the fused CP4-Aβ construct assembled into antiparallel β- sheets and amyloidmore » fibrils, a 4.0-fold increase in the hydrolysis rate of p-nitrophenyl acetate (p-NPA) compared to neat CP4 peptide was observed. Furthermore, the enhanced catalytic activity of CP4-Aβ assembly could be explained both by pre-organization of a catalytically competent Ser-His-acid triad and hydrophobic stabilization of a bound substrate between the triad and p-NPA, indicating that a design strategy for self-assembled peptides is important to accomplish the desired functionality.« less

The Multi Domain Caldicellulosiruptor bescii CelA Cellulase Excels at the Hydrolysis of Crystalline Cellulose

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brunecky, Roman; Donohoe, Bryon S.; Yarbrough, John M.

The crystalline nature of cellulose microfibrils is one of the key factors influencing biomass recalcitrance which is a key technical and economic barrier to overcome to make cellulosic biofuels a commercial reality. To date, all known fungal enzymes tested have great difficulty degrading highly crystalline cellulosic substrates. We have demonstrated that the CelA cellulase from Caldicellulosiruptor bescii degrades highly crystalline cellulose as well as low crystallinity substrates making it the only known cellulase to function well on highly crystalline cellulose. Unlike the secretomes of cellulolytic fungi, which typically comprise multiple, single catalytic domain enzymes for biomass degradation, some bacterial systemsmore » employ an alternative strategy that utilizes multi-catalytic domain cellulases. Additionally, CelA is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Furthermore we have determined that the factors negatively affecting digestion of lignocellulosic materials by C. bescii enzyme cocktails containing CelA appear to be significantly different from the performance barriers affecting fungal cellulases. Furthermore, we explore the activity and degradation mechanism of CelA on a variety of pretreated substrates to better understand how the different bulk components of biomass, such as xylan and lignin, impact its performance.« less

The Multi Domain Caldicellulosiruptor bescii CelA Cellulase Excels at the Hydrolysis of Crystalline Cellulose

DOE PAGES

Brunecky, Roman; Donohoe, Bryon S.; Yarbrough, John M.; ...

2017-08-29

The crystalline nature of cellulose microfibrils is one of the key factors influencing biomass recalcitrance which is a key technical and economic barrier to overcome to make cellulosic biofuels a commercial reality. To date, all known fungal enzymes tested have great difficulty degrading highly crystalline cellulosic substrates. We have demonstrated that the CelA cellulase from Caldicellulosiruptor bescii degrades highly crystalline cellulose as well as low crystallinity substrates making it the only known cellulase to function well on highly crystalline cellulose. Unlike the secretomes of cellulolytic fungi, which typically comprise multiple, single catalytic domain enzymes for biomass degradation, some bacterial systemsmore » employ an alternative strategy that utilizes multi-catalytic domain cellulases. Additionally, CelA is extremely thermostable and highly active at elevated temperatures, unlike commercial fungal cellulases. Furthermore we have determined that the factors negatively affecting digestion of lignocellulosic materials by C. bescii enzyme cocktails containing CelA appear to be significantly different from the performance barriers affecting fungal cellulases. Furthermore, we explore the activity and degradation mechanism of CelA on a variety of pretreated substrates to better understand how the different bulk components of biomass, such as xylan and lignin, impact its performance.« less

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

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

PubMed

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

2016-07-05

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.

HeLa Cells Containing a Truncated Form of DNA Polymerase Beta are More Sensitized to Alkylating Agents than to Agents Inducing Oxidative Stress.

PubMed

Khanra, Kalyani; Chakraborty, Anindita; Bhattacharyya, Nandan

2015-01-01

The present study was aimed at determining the effects of alkylating and oxidative stress inducing agents on a newly identified variant of DNA polymerase beta (polβ Δ208-304) specific for ovarian cancer. Pol β Δ208-304 has a deletion of exons 11-13 which lie in the catalytic part of enzyme. We compared the effect of these chemicals on HeLa cells and HeLa cells stably transfected with this variant cloned into in pcDNAI/neo vector by MTT, colony forming and apoptosis assays. Polβ Δ208-304 cells exhibited greater sensitivity to an alkylating agent and less sensitivity towards H2O2 and UV when compared with HeLa cells alone. It has been shown that cell death in Pol β Δ208-304 transfected HeLa cells is mediated by the caspase 9 cascade. Exon 11 has nucleotidyl selection activity, while exons 12 and 13 have dNTP selection activity. Hence deletion of this part may affect polymerizing activity although single strand binding and double strand binding activity may remain same. The lack of this part may adversely affect catalytic activity of DNA polymerase beta so that the variant may act as a dominant negative mutant. This would represent clinical significance if translated into a clinical setting because resistance to radiation or chemotherapy during the relapse of the disease could be potentially overcome by this approach.

Critical Role of Interdomain Interactions in the Conformational Change and Catalytic Mechanism of Endoplasmic Reticulum Aminopeptidase 1.

PubMed

Stamogiannos, Athanasios; Maben, Zachary; Papakyriakou, Athanasios; Mpakali, Anastasia; Kokkala, Paraskevi; Georgiadis, Dimitris; Stern, Lawrence J; Stratikos, Efstratios

2017-03-14

Endoplasmic reticulum aminopeptidase 1 (ERAP1) is an intracellular enzyme that is important for the generation of antigenic epitopes and major histocompatibility class I-restricted adaptive immune responses. ERAP1 processes a vast variety of different peptides but still shows length and sequence selectivity, although the mechanism behind these properties is poorly understood. X-ray crystallographic analysis has revealed that ERAP1 can assume at least two distinct conformations in which C-terminal domain IV is either proximal or distal to active site domain II. To improve our understanding of the role of this conformational change in the catalytic mechanism of ERAP1, we used site-directed mutagenesis to perturb key salt bridges between domains II and IV. Enzymatic analysis revealed that these mutations, although located away from the catalytic site, greatly reduce the catalytic efficiency and change the allosteric kinetic behavior. The variants were more efficiently activated by small peptides and bound a competitive inhibitor with weaker affinity and faster dissociation kinetics. Molecular dynamics analysis suggested that the mutations affect the conformational distribution of ERAP1, reducing the population of closed states. Small-angle X-ray scattering indicated that both the wild type and the ERAP1 variants are predominantly in an open conformational state in solution. Overall, our findings suggest that electrostatic interactions between domains II and IV in ERAP1 are crucial for driving a conformational change that regulates the structural integrity of the catalytic site. The extent of domain opening in ERAP1 probably underlies its specialization for antigenic peptide precursors and should be taken into account in inhibitor development efforts.

Formation of alcohol conversion catalysts

DOEpatents

Wachs, Israel E.; Cai, Yeping

2001-01-01

The method of the present invention involves a composition containing an intimate mixture of (a) metal oxide support particles and (b) a catalytically active metal oxide from Groups VA, VIA, or VIIA, its method of manufacture, and its method of use for converting alcohols to aldehydes. During the conversion process, catalytically active metal oxide from the discrete catalytic metal oxide particles migrates to the oxide support particles and forms a monolayer of catalytically active metal oxide on the oxide support particle to form a catalyst composition having a higher specific activity than the admixed particle composition.

IFCC primary reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C. Part 9: reference procedure for the measurement of catalytic concentration of alkaline phosphatase International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) Scientific Division, Committee on Reference Systems of Enzymes (C-RSE) (1)).

PubMed

Schumann, Gerhard; Klauke, Rainer; Canalias, Francesca; Bossert-Reuther, Steffen; Franck, Paul F H; Gella, F-Javier; Jørgensen, Poul J; Kang, Dongchon; Lessinger, Jean-Marc; Panteghini, Mauro; Ceriotti, Ferruccio

2011-09-01

Abstract This paper is the ninth in a series dealing with reference procedures for the measurement of catalytic activity concentrations of enzymes at 37 °C and the certification of reference preparations. Other parts deal with: Part 1. The concept of reference procedures for the measurement of catalytic activity concentrations of enzymes; Part 2. Reference procedure for the measurement of catalytic concentration of creatine kinase; Part 3. Reference procedure for the measurement of catalytic concentration of lactate dehydrogenase; Part 4. Reference procedure for the measurement of catalytic concentration of alanine aminotransferase; Part 5. Reference procedure for the measurement of catalytic concentration of aspartate aminotransferase; Part 6. Reference procedure for the measurement of catalytic concentration of γ-glutamyltransferase; Part 7. Certification of four reference materials for the determination of enzymatic activity of γ-glutamyltransferase, lactate dehydrogenase, alanine aminotransferase and creatine kinase at 37 °C; Part 8. Reference procedure for the measurement of catalytic concentration of α-amylase. The procedure described here is derived from the previously described 30 °C IFCC reference method. Differences are tabulated and commented on in Appendix 1.

Bio-oil from fast pyrolysis of lignin: Effects of process and upgrading parameters.

PubMed

Fan, Liangliang; Zhang, Yaning; Liu, Shiyu; Zhou, Nan; Chen, Paul; Cheng, Yanling; Addy, Min; Lu, Qian; Omar, Muhammad Mubashar; Liu, Yuhuan; Wang, Yunpu; Dai, Leilei; Anderson, Erik; Peng, Peng; Lei, Hanwu; Ruan, Roger

2017-10-01

Effects of process parameters on the yield and chemical profile of bio-oil from fast pyrolysis of lignin and the processes for lignin-derived bio-oil upgrading were reviewed. Various process parameters including pyrolysis temperature, reactor types, lignin characteristics, residence time, and feeding rate were discussed and the optimal parameter conditions for improved bio-oil yield and quality were concluded. In terms of lignin-derived bio-oil upgrading, three routes including pretreatment of lignin, catalytic upgrading, and co-pyrolysis of hydrogen-rich materials have been investigated. Zeolite cracking and hydrodeoxygenation (HDO) treatment are two main methods for catalytic upgrading of lignin-derived bio-oil. Factors affecting zeolite activity and the main zeolite catalytic mechanisms for lignin conversion were analyzed. Noble metal-based catalysts and metal sulfide catalysts are normally used as the HDO catalysts and the conversion mechanisms associated with a series of reactions have been proposed. Copyright © 2017 Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roland, Bartholomew P.; Amrich, Christopher G.; Kammerer, Charles J.

Triosephosphate isomerase (TPI) is a glycolytic enzyme which homodimerizes for full catalytic activity. Mutations of the TPI gene elicit a disease known as TPI Deficiency, a glycolytic enzymopathy noted for its unique severity of neurological symptoms. Evidence suggests that TPI Deficiency pathogenesis may be due to conformational changes of the protein, likely affecting dimerization and protein stability. In this report, we genetically and physically characterize a human disease-associated TPI mutation caused by an I170V substitution. Human TPI I170V elicits behavioral abnormalities in Drosophila. An examination of hTPI I170V enzyme kinetics revealed this substitution reduced catalytic turnover, while assessments of thermalmore » stability demonstrated an increase in enzyme stability. Furthermore, the crystal structure of the homodimeric I170V mutant reveals changes in the geometry of critical residues within the catalytic pocket. In the end, collectively these data reveal new observations of the structural and kinetic determinants of TPI deficiency pathology, providing new insights into disease pathogenesis.« less

Role of regulatory subunits and protein kinase inhibitor (PKI) in determining nuclear localization and activity of the catalytic subunit of protein kinase A.

PubMed

Wiley, J C; Wailes, L A; Idzerda, R L; McKnight, G S

1999-03-05

Regulation of protein kinase A by subcellular localization may be critical to target catalytic subunits to specific substrates. We employed epitope-tagged catalytic subunit to correlate subcellular localization and gene-inducing activity in the presence of regulatory subunit or protein kinase inhibitor (PKI). Transiently expressed catalytic subunit distributed throughout the cell and induced gene expression. Co-expression of regulatory subunit or PKI blocked gene induction and prevented nuclear accumulation. A mutant PKI lacking the nuclear export signal blocked gene induction but not nuclear accumulation, demonstrating that nuclear export is not essential to inhibit gene induction. When the catalytic subunit was targeted to the nucleus with a nuclear localization signal, it was not sequestered in the cytoplasm by regulatory subunit, although its activity was completely inhibited. PKI redistributed the nuclear catalytic subunit to the cytoplasm and blocked gene induction, demonstrating that the nuclear export signal of PKI can override a strong nuclear localization signal. With increasing PKI, the export process appeared to saturate, resulting in the return of catalytic subunit to the nucleus. These results demonstrate that both the regulatory subunit and PKI are able to completely inhibit the gene-inducing activity of the catalytic subunit even when the catalytic subunit is forced to concentrate in the nuclear compartment.

Immobilization of pectinase on silica-based supports: Impacts of particle size and spacer arm on the activity.

PubMed

Alagöz, Dilek; Tükel, S Seyhan; Yildirim, Deniz

2016-06-01

The pectinase was separately immobilized onto Florisil and nano silica supports through both glutaraldehyde and 3-glyoxypropyltrietoxysilane spacer arms. The effects of spacer arm, particle size of support and ionic liquids on the activities of pectinase preparations were investigated. The immobilization of pectinase onto Florisil and nano silica through 3-glyoxypropyltrietoxysilane spacer arm completely led to inactivation of enzyme; however, 10 and 75% pectinase activity were retained when it was immobilized through glutaraldehyde spacer arm onto Florisil and nano silica, respectively. The pectinase immobilized onto nano silica through glutaraldehyde spacer arm showed 6.3-fold higher catalytic efficiency than that of the pectinase immobilized onto Florisil through same spacer arm. A 2.3-fold increase in thermal stability of pectinase was provided upon immobilization onto nano silica at 35°C. The effects of IL/buffer mixture and volume ratio of IL/buffer mixture on the catalytic activities of free and immobilized pectinase preparations were also tested. All the pectinase preparations showed highest activity in 10% (v/v) 1-butyl-3-methylimidazolium hexafluorophosphate containing medium and their activities significantly affected from the concentration of 1-butyl-3-methylimidazolium hexafluorophosphate. Copyright © 2016 Elsevier B.V. All rights reserved.

Heterogeneous Molecular Catalysis of Electrochemical Reactions: Volcano Plots and Catalytic Tafel Plots.

PubMed

Costentin, Cyrille; Savéant, Jean-Michel

2017-06-14

We analyze here, in the framework of heterogeneous molecular catalysis, the reasons for the occurrence or nonoccurrence of volcanoes upon plotting the kinetics of the catalytic reaction versus the stabilization free energy of the primary intermediate of the catalytic process. As in the case of homogeneous molecular catalysis or catalysis by surface-active metallic sites, a strong motivation of such studies relates to modern energy challenges, particularly those involving small molecules, such as water, hydrogen, oxygen, proton, and carbon dioxide. This motivation is particularly pertinent for what concerns heterogeneous molecular catalysis, since it is commonly preferred to homogeneous molecular catalysis by the same molecules if only for chemical separation purposes and electrolytic cell architecture. As with the two other catalysis modes, the main drawback of the volcano plot approach is the basic assumption that the kinetic responses depend on a single descriptor, viz., the stabilization free energy of the primary intermediate. More comprehensive approaches, investigating the responses to the maximal number of experimental factors, and conveniently expressed as catalytic Tafel plots, should clearly be preferred. This is more so in the case of heterogeneous molecular catalysis in that additional transport factors in the supporting film may additionally affect the current-potential responses. This is attested by the noteworthy presence of maxima in catalytic Tafel plots as well as their dependence upon the cyclic voltammetric scan rate.

Functional characterization of enzymes catalyzing ceramide phosphoethanolamine biosynthesis in mice.

PubMed

Bickert, Andreas; Ginkel, Christina; Kol, Matthijs; vom Dorp, Katharina; Jastrow, Holger; Degen, Joachim; Jacobs, René L; Vance, Dennis E; Winterhager, Elke; Jiang, Xian-Cheng; Dörmann, Peter; Somerharju, Pentti; Holthuis, Joost C M; Willecke, Klaus

2015-04-01

Besides bulk amounts of SM, mammalian cells produce small quantities of the SM analog ceramide phosphoethanolamine (CPE). Little is known about the biological role of CPE or enzymes responsible for CPE production. Heterologous expression studies revealed that SM synthase (SMS)2 is a bifunctional enzyme producing both SM and CPE, whereas SMS-related protein (SMSr) serves as monofunctional CPE synthase. Acute disruption of SMSr catalytic activity in cultured cells causes a rise in endoplasmic reticulum (ER) ceramides, fragmentation of ER exit sites, and induction of mitochondrial apoptosis. To address the relevance of CPE biosynthesis in vivo, we analyzed the tissue-specific distribution of CPE in mice and generated mouse lines lacking SMSr and SMS2 catalytic activity. We found that CPE levels were >300-fold lower than SM in all tissues examined. Unexpectedly, combined inactivation of SMSr and SMS2 significantly reduced, but did not eliminate, tissue-specific CPE pools and had no obvious impact on mouse development or fertility. While SMSr is widely expressed and serves as the principal CPE synthase in the brain, blocking its catalytic activity did not affect ceramide levels or secretory pathway integrity in the brain or any other tissue. Our data provide a first inventory of CPE species and CPE-biosynthetic enzymes in mammals. Copyright © 2015 by the American Society for Biochemistry and Molecular Biology, Inc.

PXR-Mediated Upregulation of CYP3A Expression by Herb Compound Praeruptorin C from Peucedanum praeruptorum Dunn

PubMed Central

Huang, Ling; Wu, Qian; Li, Yu-Hua; Wang, Yi-Tao; Bi, Hui-Chang

2013-01-01

We recently reported that Praeruptorin C effectively transactivated the mRNA, protein expression, and catalytic activity of CYP3A4 via the CAR-mediated pathway, but whether and how PC could affect the expression and catalytic activity of CYP3A4 via PXR pathway remains unknown. Therefore, in this study, the effect of PC on the CYP3A gene expression was investigated in mice primary hepatocytes after knockdown of PXR by transient transfection of PXR siRNA, and the gene expression, protein expression, and catalytic activity of CYP3A4 in the LS174T cells with PXR overexpression were determined by real-time PCR, western blot analysis, and LC-MS/MS-based CYP3A4 substrate assay, respectively. We found that the level of CYP3a11 gene expression in mouse primary hepatocytes was significantly increased by praeruptorin C, but such an induction was suppressed after knockdown of pregnane X receptor by its siRNA. In PXR-overexpressed LS174T cells, PC significantly enhanced CYP3A4 mRNA, protein expression, and functional activity through PXR-mediated pathway; conversely, no such increase was found in the untransfected cells. These findings suggest that PC can significantly upregulate CYP3A level via the PXR-mediated pathway, and this should be taken into consideration to predict any potential herb-drug interactions between PC, Qianhu, and the other coadministered drugs. PMID:24379885

Analysis of the active site mechanism of Tyrosyl-DNA phosphodiesterase I: a member of the phospholipase D superfamily

PubMed Central

Gajewski, Stefan; Comeaux, Evan Q.; Jafari, Nauzanene; Bharatham, Nagakumar; Bashford, Donald; White, Stephen W.; van Waardenburg, Robert C.A.M.

2011-01-01

Tyrosyl DNA phosphodiesterase I (Tdp1) is a member of the phospholipase D superfamily and hydrolyzes 3′phospho-DNA adducts via two conserved catalytic histidines, one acting as the lead nucleophile and the second as a general acid/base. Substitution of the second histidine specifically to arginine contributes to the neurodegenerative disease SCAN1. We investigated the catalytic role of this histidine in the yeast protein (His432) using a combination of X-ray crystallography, biochemistry, yeast genetics and theoretical chemistry. The structures of wild type Tdp1 and His432Arg both show a phosphorylated form of the nucleophilic histidine that is not observed in the structure of His432Asn. The phosphohistidine is stabilized in the His432Arg structure by the guanidinium group that also restricts access of a nucleophilic water molecule to the Tdp1-DNA intermediate. Biochemical analyses confirm that His432Arg forms an observable and unique Tdp1-DNA adduct during catalysis. Substitution of His432 by Lys does not affect catalytic activity or yeast phenotype, but substitution with Asn, Gln, Leu, Ala, Ser and Thr all result in severely compromised enzymes and Top1-camptothecin dependent lethality. Surprisingly, His432Asn did not show a stable covalent Tdp1-DNA intermediate which suggests another catalytic defect. Theoretical calculations revealed that the defect resides in the nucleophilic histidine and that the pKa of this histidine is crucially dependent upon the second histidine and the incoming phosphate of the substrate. This represents a unique example of substrate-activated catalysis that applies to the entire phospholipase D superfamily. PMID:22155078

Analysis of the Active-Site Mechanism of Tyrosyl-DNA Phosphodiesterase I: A Member of the Phospholipase D Superfamily

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gajewski, Stefan; Comeaux, Evan Q.; Jafari, Nauzanene

2012-03-15

Tyrosyl-DNA phosphodiesterase I (Tdp1) is a member of the phospholipase D superfamily that hydrolyzes 3'-phospho-DNA adducts via two conserved catalytic histidines - one acting as the lead nucleophile and the second acting as a general acid/base. Substitution of the second histidine specifically to arginine contributes to the neurodegenerative disease spinocerebellar ataxia with axonal neuropathy (SCAN1). We investigated the catalytic role of this histidine in the yeast protein (His432) using a combination of X-ray crystallography, biochemistry, yeast genetics, and theoretical chemistry. The structures of wild-type Tdp1 and His432Arg both show a phosphorylated form of the nucleophilic histidine that is not observedmore » in the structure of His432Asn. The phosphohistidine is stabilized in the His432Arg structure by the guanidinium group that also restricts the access of nucleophilic water molecule to the Tdp1-DNA intermediate. Biochemical analyses confirm that His432Arg forms an observable and unique Tdp1-DNA adduct during catalysis. Substitution of His432 by Lys does not affect catalytic activity or yeast phenotype, but substitutions with Asn, Gln, Leu, Ala, Ser, and Thr all result in severely compromised enzymes and DNA topoisomerase I-camptothecin dependent lethality. Surprisingly, His432Asn did not show a stable covalent Tdp1-DNA intermediate that suggests another catalytic defect. Theoretical calculations revealed that the defect resides in the nucleophilic histidine and that the pK{sub a} of this histidine is crucially dependent on the second histidine and on the incoming phosphate of the substrate. This represents a unique example of substrate-activated catalysis that applies to the entire phospholipase D superfamily.« less

Heterogeneous Ag-TiO2-SiO2 composite materials as novel catalytic systems for selective epoxidation of cyclohexene by H2O2

PubMed Central

Wang, Xin; Xue, Jianyue; Wang, Xinyun; Liu, Xiaoheng

2017-01-01

TiO2-SiO2 composites were synthesized using cetyl trimethyl ammonium bromide (CTAB) as the structure directing template. Self-assembly hexadecyltrimethyl- ammonium bromide TiO2-SiO2/(CTAB) were soaked into silver nitrate (AgNO3) aqueous solution. The Ag-TiO2-SiO2(Ag-TS) composite were prepared via a precipitation of AgBr in soaking process and its decomposition at calcination stage. Structural characterization of the materials was carried out by various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-desorption and ultraviolet visible spectroscopy (UV-Vis). Characterization results revealed that Ag particles were incorporated into hierarchical TiO2-SiO2 without significantly affecting the structures of the supports. Further heating-treatment at 723 K was more favorable for enhancing the stability of the Ag-TS composite. The cyclohexene oxide was the major product in the epoxidation using H2O2 as the oxidant over the Ag-TS catalysts. Besides, the optimum catalytic activity and stability of Ag-TS catalysts were obtained under operational conditions of calcined at 723 K for 2 h, reaction time of 120 min, reaction temperature of 353 K, catalyst amount of 80 mg, aqueous H2O2 (30 wt.%) as oxidant and chloroform as solvent. High catalytic activity with conversion rate up to 99.2% of cyclohexene oxide could be obtainable in water-bathing. The catalyst was found to be stable and could be reused three times without significant loss of catalytic activity under the optimized reaction conditions. PMID:28493879

All the catalytic active sites of MoS 2 for hydrogen evolution

DOE PAGES

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

2016-11-29

MoS 2 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 MoS 2, 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 tomore » 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 MoS 2 is higher than that in low crystalline quality MoS 2, which may be related with the proximity of different local crystalline structures to the vacancies.« less

Enhanced catalyst activity by decorating of Au on Ag@Cu2O nanoshell

NASA Astrophysics Data System (ADS)

Chen, Lei; Liu, Maomao; Zhao, Yue; Kou, Qiangwei; Wang, Yaxin; Liu, Yang; Zhang, Yongjun; Yang, Jinghai; Jung, Young Mee

2018-03-01

We successfully synthesized Au-decorated Ag@Cu2O heterostructures via a simple galvanic replacement method. As the Au precursor concentration increased, the density of the Au nanoparticles (NPs) on the Ag@Cu2O surface increased, which changed the catalytic activity of the Ag@Cu2O-Au structure. The combination of Au, Ag, and Cu2O exhibited excellent catalytic properties, which can further effect on the catalyst activity of the Ag@Cu2O-Au structure. In addition, the proposed Ag@Cu2O-Au nanocomposite was used to transform the organic, toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative via a catalytic reduction to optimize the material performance. The proposed Au-decorated Ag@Cu2O exhibited excellent catalytic activity, and the catalytic reduction time greatly decreased (5 min). Thus, three novel properties of Ag@Cu2O-Au, i.e., charge redistribution and transfer, adsorption, and catalytic reduction of organic pollutants, were ascertained for water remediation. The proposed catalytic properties have potential applications for photocatalysis and localized surface plasmon resonance (LSPR)- and peroxidase-like catalysis.

Select human cancer mutants of NRMT1 alter its catalytic activity and decrease N-terminal trimethylation.

PubMed

Shields, Kaitlyn M; Tooley, John G; Petkowski, Janusz J; Wilkey, Daniel W; Garbett, Nichola C; Merchant, Michael L; Cheng, Alan; Schaner Tooley, Christine E

2017-08-01

A subset of B-cell lymphoma patients have dominant mutations in the histone H3 lysine 27 (H3K27) methyltransferase EZH2, which change it from a monomethylase to a trimethylase. These mutations occur in aromatic resides surrounding the active site and increase growth and alter transcription. We study the N-terminal trimethylase NRMT1 and the N-terminal monomethylase NRMT2. They are 50% identical, but differ in key aromatic residues in their active site. Given how these residues affect EZH2 activity, we tested whether they are responsible for the distinct catalytic activities of NRMT1/2. Additionally, NRMT1 acts as a tumor suppressor in breast cancer cells. Its loss promotes oncogenic phenotypes but sensitizes cells to DNA damage. Mutations of NRMT1 naturally occur in human cancers, and we tested a select group for altered activity. While directed mutation of the aromatic residues had minimal catalytic effect, NRMT1 mutants N209I (endometrial cancer) and P211S (lung cancer) displayed decreased trimethylase and increased monomethylase/dimethylase activity. Both mutations are located in the peptide-binding channel and indicate a second structural region impacting enzyme specificity. The NRMT1 mutants demonstrated a slower rate of trimethylation and a requirement for higher substrate concentration. Expression of the mutants in wild type NRMT backgrounds showed no change in N-terminal methylation levels or growth rates, demonstrating they are not acting as dominant negatives. Expression of the mutants in cells lacking endogenous NRMT1 resulted in minimal accumulation of N-terminal trimethylation, indicating homozygosity could help drive oncogenesis or serve as a marker for sensitivity to DNA damaging chemotherapeutics or γ-irradiation. © 2017 The Protein Society.

Remote Exosites of the Catalytic Domain of Matrix Metalloproteinase-12 Enhance Elastin Degradation┼

PubMed Central

Fulcher, Yan G.; Van Doren, Steven R.

2011-01-01

How does matrix metalloproteinase-12 (MMP-12 or metalloelastase) degrade elastin with high specific activity? NMR suggested soluble elastin to cover surfaces of MMP-12 far from its active site. Two of these surfaces have been found, by mutagenesis guided by the BINDSIght approach, to affect degradation and affinity for elastin substrates but not a small peptide substrate. Main exosite 1 has been extended out to Asp124 that binds calcium. Novel exosite 2 comprises residues from the II–III loop and β-strand I near the back of the catalytic domain. The high exposure of these distal exosites may make them accessible to elastin made more flexible by partial hydrolysis. Importantly, combination of a lesion at each of exosites 1 and 2 and active site decreased catalytic competence towards soluble elastin by 13- to 18-fold to the level of MMP-3, homologue and poor elastase. Double mutant cycle analysis of conservative mutations of Met156 (exosite 2) and either Asp124 (exosite 1) or Ile180 (active site) had additive effects. Compared to polar substitutions observed in other MMPs, Met156 enhanced affinity and Ile180 kcat for soluble elastin. Both residues detracted from the higher folding stability with polar mutations. This resembles the trend in enzymes of an inverse relationship between folding stability and activity. Restoring Asp124 from combination mutants enhanced kcat for soluble elastin. In elastin degradation, exosites 1 and 2 contributed independently of each other and Ile180 at the active site, but with partial coupling to Ala182 near the active site. The concept of weak, separated interactions coalescing somewhat independently can be extended to this proteolytic digestion of a protein from fibrils. PMID:21967233

Modulation of individual steps in group I intron catalysis by a peripheral metal ion.

PubMed

Forconi, Marcello; Piccirilli, Joseph A; Herschlag, Daniel

2007-10-01

Enzymes are complex macromolecules that catalyze chemical reactions at their active sites. Important information about catalytic interactions is commonly gathered by perturbation or mutation of active site residues that directly contact substrates. However, active sites are engaged in intricate networks of interactions within the overall structure of the macromolecule, and there is a growing body of evidence about the importance of peripheral interactions in the precise structural organization of the active site. Here, we use functional studies, in conjunction with published structural information, to determine the effect of perturbation of a peripheral metal ion binding site on catalysis in a well-characterized catalytic RNA, the Tetrahymena thermophila group I ribozyme. We perturbed the metal ion binding site by site-specifically introducing a phosphorothioate substitution in the ribozyme's backbone, replacing the native ligands (the pro-R (P) oxygen atoms at positions 307 and 308) with sulfur atoms. Our data reveal that these perturbations affect several reaction steps, including the chemical step, despite the absence of direct contacts of this metal ion with the atoms involved in the chemical transformation. As structural probing with hydroxyl radicals did not reveal significant change in the three-dimensional structure upon phosphorothioate substitution, the effects are likely transmitted through local, rather subtle conformational rearrangements. Addition of Cd(2+), a thiophilic metal ion, rescues some reaction steps but has deleterious effects on other steps. These results suggest that native interactions in the active site may have been aligned by the naturally occurring peripheral residues and interactions to optimize the overall catalytic cycle.

TiO2-nanowire/MWCNT composite with enhanced performance and durability for polymer electrolyte fuel cells

NASA Astrophysics Data System (ADS)

Selvaganesh, S. Vinod; Dhanasekaran, P.; Bhat, Santoshkumar D.

2017-12-01

Durability is a major issue and has been the growing focus of research for the commercialization of polymer electrolyte fuel cells (PEFCs). Corrosion of carbon support is a key parameter as it triggers the Pt catalyst degradation and affects cell performance, which in turn affects the longevity of the cells. Herein, we describe a hybrid composite support of TiO2-nanowires and Multiwalled carbon nanotubes (MWCNTs) that offers resistance to corrosion under stressful operating conditions. Titania nanowireswhich have been shown to be more efficient and catalytically active than spherically shaped TiO2. TiO2-MWCNT composites are prepared through a hydrothermal method, followed by Pt deposition using a polyol method. Crystal structure, morphology, and oxidation state are examined through various characterization techniques. Electrochemical performance of TiO2-nanowire/MWCNT composite-supported Pt at various ratios of TiO2/MWCNT is assessed in PEFCs. Pt on support with optimum composition of TiO2-nanowires to MWCNTs exhibits fuel cell performance superior to Pt onMWCNTs. Accelerated stress testing (AST) between 1 and 1.5 V reveals that the designed catalyst on nanocomposite support possesses superior electrochemical activity and shows only 16% loss in catalytic activity in relation to 35% for Pt/MWCNTs even after 6000 potential cycles. Subsequently, the samples were characterized after AST to correlate the loss in fuel cell performance

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

PubMed

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

2016-01-28

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

Hydrogenation of CO 2 on ZnO/Cu(100) and ZnO/Cu(111) Catalysts: Role of Copper Structure and Metal–Oxide Interface in Methanol Synthesis

DOE PAGES

Palomino, Robert M.; Ramirez, Pedro J.; Liu, Zongyuan; ...

2017-08-21

The results of kinetic tests and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) show the important role played by a ZnO–copper interface in the generation of CO and the synthesis of methanol from CO 2 hydrogenation. The deposition of nanoparticles of ZnO on Cu(100) and Cu(111), θ oxi < 0.3 monolayer, produces highly active catalysts. The catalytic activity of these systems increases in the sequence: Cu(111) < Cu(100) < ZnO/Cu(111) < ZnO/Cu(100). The structure of the copper substrate influences the catalytic performance of a ZnO–copper interface. Furthermore, size and metal–oxide interactions affect the chemical and catalytic properties of the oxide making themore » supported nanoparticles different from bulk ZnO. The formation of a ZnO–copper interface favors the binding and conversion of CO 2 into a formate intermediate that is stable on the catalyst surface up to temperatures above 500 K. Alloys of Zn with Cu(111) and Cu(100) were not stable at the elevated temperatures (500–600 K) used for the CO 2 hydrogenation reaction. However, reaction with CO 2 oxidized the zinc, enhancing its stability over the copper substrates.« less

Hydrogenation of CO 2 on ZnO/Cu(100) and ZnO/Cu(111) Catalysts: Role of Copper Structure and Metal–Oxide Interface in Methanol Synthesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Palomino, Robert M.; Ramirez, Pedro J.; Liu, Zongyuan

The results of kinetic tests and ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) show the important role played by a ZnO–copper interface in the generation of CO and the synthesis of methanol from CO 2 hydrogenation. The deposition of nanoparticles of ZnO on Cu(100) and Cu(111), θ oxi < 0.3 monolayer, produces highly active catalysts. The catalytic activity of these systems increases in the sequence: Cu(111) < Cu(100) < ZnO/Cu(111) < ZnO/Cu(100). The structure of the copper substrate influences the catalytic performance of a ZnO–copper interface. Furthermore, size and metal–oxide interactions affect the chemical and catalytic properties of the oxide making themore » supported nanoparticles different from bulk ZnO. The formation of a ZnO–copper interface favors the binding and conversion of CO 2 into a formate intermediate that is stable on the catalyst surface up to temperatures above 500 K. Alloys of Zn with Cu(111) and Cu(100) were not stable at the elevated temperatures (500–600 K) used for the CO 2 hydrogenation reaction. However, reaction with CO 2 oxidized the zinc, enhancing its stability over the copper substrates.« less

The surface plasmon-induced hot carrier effect on the catalytic activity of CO oxidation on a Cu2O/hexoctahedral Au inverse catalyst.

PubMed

Lee, Si Woo; Hong, Jong Wook; Lee, Hyunhwa; Wi, Dae Han; Kim, Sun Mi; Han, Sang Woo; Park, Jeong Young

2018-06-14

The intrinsic correlation between an enhancement of catalytic activity and the flow of hot electrons generated at metal-oxide interfaces suggests an intriguing way to control catalytic reactions and is a significant subject in heterogeneous catalysis. Here, we show surface plasmon-induced catalytic enhancement by the peculiar nanocatalyst design of hexoctahedral (HOH) Au nanocrystals (NCs) with Cu2O clusters. We found that this inverse catalyst comprising a reactive oxide for the catalytic portion and a metal as the source of electrons by localized surface plasmon resonance (localized SPR) exhibits a change in catalytic activity by direct hot electron transfer or plasmon-induced resonance energy transfer (PIRET) when exposed to light. We prepared two types of inverse catalysts, Cu2O at the vertex sites of HOH Au NCs (Cu2O/Au vertex site) and a HOH Au NC-Cu2O core-shell structure (HOH Au@Cu2O), to test the structural effect on surface plasmons. Under broadband light illumination, the Cu2O/Au vertex site catalyst showed 30-90% higher catalytic activity and the HOH Au@Cu2O catalyst showed 10-30% higher catalytic activity than when in the dark. Embedding thin SiO2 layers between the HOH Au NCs and the Cu2O verified that the dominant mechanism for the catalytic enhancement is direct hot electron transfer from the HOH Au to the Cu2O. Finite-difference time domain calculations show that a much stronger electric field was formed on the vertex sites after growing the Cu2O on the HOH Au NCs. These results imply that the catalytic activity is enhanced when hot electrons, created from photon absorption on the HOH Au metal and amplified by the presence of surface plasmons, are transferred to the reactive Cu2O.

Charge neutralization in the active site of the catalytic trimer of aspartate transcarbamoylase promotes diverse structural changes.

PubMed

Endrizzi, James A; Beernink, Peter T

2017-11-01

A classical model for allosteric regulation of enzyme activity posits an equilibrium between inactive and active conformations. An alternative view is that allosteric activation is achieved by increasing the potential for conformational changes that are essential for catalysis. In the present study, substitution of a basic residue in the active site of the catalytic (C) trimer of aspartate transcarbamoylase with a non-polar residue results in large interdomain hinge changes in the three chains of the trimer. One conformation is more open than the chains in both the wild-type C trimer and the catalytic chains in the holoenzyme, the second is closed similar to the bisubstrate-analog bound conformation and the third hinge angle is intermediate to the other two. The active-site 240s loop conformation is very different between the most open and closed chains, and is disordered in the third chain, as in the holoenzyme. We hypothesize that binding of anionic substrates may promote similar structural changes. Further, the ability of the three catalytic chains in the trimer to access the open and closed active-site conformations simultaneously suggests a cyclic catalytic mechanism, in which at least one of the chains is in an open conformation suitable for substrate binding whereas another chain is closed for catalytic turnover. Based on the many conformations observed for the chains in the isolated catalytic trimer to date, we propose that allosteric activation of the holoenzyme occurs by release of quaternary constraint into an ensemble of active-site conformations. © 2017 The Protein Society.

Preparation of Cu@Cu₂O Nanocatalysts by Reduction of HKUST-1 for Oxidation Reaction of Catechol.

PubMed

Jang, Seongwan; Yoon, Chohye; Lee, Jae Myung; Park, Sungkyun; Park, Kang Hyun

2016-11-02

HKUST-1, a copper-based metal organic framework (MOF), has been investigated as a catalyst in various reactions. However, the HKUST-1 shows low catalytic activity in the oxidation of catechol. Therefore, we synthesized Fe₃O₄@HKUST-1 by layer-by layer assembly strategy and Cu@Cu₂O by reduction of HKUST-1 for enhancement of catalytic activity. Cu@Cu₂O nanoparticles exhibited highly effective catalytic activity in oxidation of 3,5-di- tert -butylcatechol. Through this method, MOF can maintain the original core-shell structure and be used in various other reactions with enhanced catalytic activity.

Influence of hot carriers on catalytic reaction; Pt nanoparticles on GaN substrates under light irradiation.

PubMed

Kim, Sun Mi; Park, Dahee; Yuk, Youngji; Kim, Sang Hoon; Park, Jeong Young

2013-01-01

We report the hot carrier-driven catalytic activity of two-dimensional arrays of Pt nanoparticles on GaN substrate under light irradiation. In order to elucidate the effect of a hot carrier in a catalytic chemical reaction, the CO oxidation reaction was carried out on Pt nanoparticles on p- and n-type GaN under light irradiation. Metal catalysts composed of Pt nanoparticles were prepared using two different preparation methods: the one-pot polyol reduction and are plasma deposition methods. Under light irradiation, the catalytic activity of the Pt nanoparticles supported on GaN exhibited a distinct change depending on the doping type. The catalytic activity of the Pt nanoparticles on the n-doped GaN wafer decreased by 8-28% under light irradiation, compared to no irradiation (i.e., in the dark), while the Pt nanoparticles on the p-doped GaN wafer increased by 11-33% under light irradiation, compared to no irradiation. The catalytic activity increased on the smaller Pt nanoparticles, compared to the larger nanoparticles, presumably due to the mean free path of hot carriers. Based on these results, we conclude that the flow of hot carriers generated at the Pt-GaN interface during light irradiation is responsible for the change in catalytic activity on the Pt nanoparticles.

The protein cofactor allows the sequence of an RNase P ribozyme to diversify by maintaining the catalytically active structure of the enzyme.

PubMed Central

Kim, J J; Kilani, A F; Zhan, X; Altman, S; Liu, F

1997-01-01

To study the effect proteins have on the catalysis and evolution of RNA enzymes, we simulated evolution of RNase P catalytic M1 RNA in vitro, in the presence and absence of its C5 protein cofactor. In the presence of C5, functional M1 sequence variants (not catalytically active in the absence of C5) were selected in addition to those identical to M1. C5 maintains the catalytically active structure of the variants and allows for an enhanced spectrum of M1 molecules to function in the context of a ribonucleoprotein (RNP) complex. The generation of an RNP enzyme, requiring both RNA and protein components, from a catalytically active RNA molecule has implications for how modern RNP complexes evolved from ancestral RNAs. PMID:9174096

Solid strong base K-Pt/NaY zeolite nano-catalytic system for completed elimination of formaldehyde at room temperature

NASA Astrophysics Data System (ADS)

Song, Shaoqing; Wu, Xi; Lu, Changhai; Wen, Meicheng; Le, Zhanggao; Jiang, Shujuan

2018-06-01

Solid strong base nano-catalytic system of K-modification NaY zeolite supported 0.08% Pt (K-Pt/NaY) were constructed for eliminating HCHO at room temperature. In the catalytic process, activation energy over K-Pt/NaY nano-catalytic system was greatly decreased along with the enhanced reaction rate. Characterization and catalytic tests revealed the surface electron structure of K-Pt/NaY was improved, as reflected by the enhanced HCHO adsorption capability, high sbnd OH concentration, and low-temperature reducibility. Therefore, the optimal K-Pt/NaY showed high catalytic efficiency and strong H2O tolerance for HCHO elimination by directly promoting the reaction between active sbnd OH and formate species. These results may suggest a new way for probing the advanced solid strong base nano-catalytic system for the catalytic elimination of indoor HCHO.

Study of Pt-Rh/CeO2-ZrO2-MxOy (M = Y, La)/Al2O3 three-way catalysts

NASA Astrophysics Data System (ADS)

Jiaxiu, Guo; Zhonghua, Shi; Dongdong, Wu; Huaqiang, Yin; Maochu, Gong; Yaoqiang, Chen

2013-05-01

CeO2-ZrO2-MxOy (M = Y; La) mixed oxides, prepared by co-precipitation method and characterized by Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Raman spectra (RM) and oxygen pulse reaction, were comparatively investigated to elucidate the combinational effects of Y and/or La oxide promoters on the catalytic activity and anti-aging performance of monolithic cordierite honeycomb catalysts with low Pt and Rh content. The catalytic activities, water-gas shift (WGS) and steam reforming reaction (SR) were studied under a simulated gas mixture. The catalysts were also characterized by H2-temperature-programmed reduction (H2-TPR) and O2-temperature-programmed desorption (O2-TPD). The results showed that the prepared CeO2-ZrO2-MxOy oxides have a face-centered cubic fluorite structure and are nanosize. La3+ ions can significantly improve thermal stability and efficiently retard CeO2-ZrO2 crystal sintering and growth. Doped CeO2-ZrO2 with Y3+ and La3+ has 105 and 60 m2/g surface area and 460 and 390 μmol/g OSC before and after aging. The T50 of fresh Pt-Rh/CZYL/LA is 170 °C for CO, 222 °C for C3H8 and 189 °C for NO, and shift to 205, 262 and 228 °C after hydrothermal aging, which are better than those of Pt-Rh/CZY/LA or Pt-Rh/CZL/LA. WGS and SR are relate to the OSC of oxygen storage materials and absorbed oxygen species on the catalyst surface and affect the three-way catalytic activities of catalysts. The reductive property of noble metals and the dissociatively adsorbed O2 on the surface of catalysts are closely related to the catalytic activities.

A Conformational Change of the γ Subunit Indirectly Regulates the Activity of Cyanobacterial F1-ATPase*

PubMed Central

Sunamura, Ei-Ichiro; Konno, Hiroki; Imashimizu, Mari; Mochimaru, Mari; Hisabori, Toru

2012-01-01

The central shaft of the catalytic core of ATP synthase, the γ subunit consists of a coiled-coil structure of N- and C-terminal α-helices, and a globular domain. The γ subunit of cyanobacterial and chloroplast ATP synthase has a unique 30–40-amino acid insertion within the globular domain. We recently prepared the insertion-removed α3β3γ complex of cyanobacterial ATP synthase (Sunamura, E., Konno, H., Imashimizu-Kobayashi, M., and Hisabori, T. (2010) Plant Cell Physiol. 51, 855–865). Although the insertion is thought to be located in the periphery of the complex and far from catalytic sites, the mutant complex shows a remarkable increase in ATP hydrolysis activity due to a reduced tendency to lapse into ADP inhibition. We postulated that removal of the insertion affects the activity via a conformational change of two central α-helices in γ. To examine this hypothesis, we prepared a mutant complex that can lock the relative position of two central α-helices to each other by way of a disulfide bond formation. The mutant obtained showed a significant change in ATP hydrolysis activity caused by this restriction. The highly active locked complex was insensitive to N-dimethyldodecylamine-N-oxide, suggesting that the complex is resistant to ADP inhibition. In addition, the lock affected ϵ inhibition. In contrast, the change in activity caused by removal of the γ insertion was independent from the conformational restriction of the central axis component. These results imply that the global conformational change of the γ subunit indirectly regulates complex activity by changing both ADP inhibition and ϵ inhibition. PMID:23012354

Interfacial Activation of Candida antarctica Lipase B: Combined Evidence from Experiment and Simulation.

PubMed

Zisis, Themistoklis; Freddolino, Peter L; Turunen, Petri; van Teeseling, Muriel C F; Rowan, Alan E; Blank, Kerstin G

2015-09-29

Lipase immobilization is frequently used for altering the catalytic properties of these industrially used enzymes. Many lipases bind strongly to hydrophobic surfaces where they undergo interfacial activation. Candida antarctica lipase B (CalB), one of the most commonly used biocatalysts, is frequently discussed as an atypical lipase lacking interfacial activation. Here we show that CalB displays an enhanced catalytic rate for large, bulky substrates when adsorbed to a hydrophobic interface composed of densely packed alkyl chains. We attribute this increased activity of more than 7-fold to a conformational change that yields a more open active site. This hypothesis is supported by molecular dynamics simulations that show a high mobility for a small "lid" (helix α5) close to the active site. Molecular docking calculations confirm that a highly open conformation of this helix is required for binding large, bulky substrates and that this conformation is favored in a hydrophobic environment. Taken together, our combined approach provides clear evidence for the interfacial activation of CalB on highly hydrophobic surfaces. In contrast to other lipases, however, the conformational change only affects large, bulky substrates, leading to the conclusion that CalB acts like an esterase for small substrates and as a lipase for substrates with large alcohol substituents.

Mussel-Inspired Polydopamine Functionalized Plasmonic Nanocomposites for Single-Particle Catalysis.

PubMed

Wang, Jun-Gang; Hua, Xin; Li, Meng; Long, Yi-Tao

2017-01-25

Polydopamine functionalized plasmonic nanocomposites with well-distributed catalytically active small gold nanoislands around large gold core were fabricated without using any chemical reductant or surfactant. The optical properties, surface molecular structures, and ensemble catalytic activity of the gold nanocomposites were investigated by time-of-flight secondary ion mass spectrometry and UV-vis spectroscopy, respectively. Moreover, the considerable catalytic activity of the nanocomposites toward 4-nitrophenol reduction was real time monitored by dark-field spectroscopy techniques at the single-nanoparticle level avoiding averaging effects in bulk systems. According to the obtained plasmonic signals from individual nanocomposites, the electron charging and discharging rates for these nanocomposites during the catalytic process were calculated. Our results offer new insights into the design and synthesis of plasmonic nanocomposites for future catalytic applications as well as a further mechanistic understanding of the electron transfer during the catalytic process at the single-nanoparticle level.

Structural and Functional Analyses of the Severe Acute Respiratory Syndrome Coronavirus Endoribonuclease Nsp15

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhardwaj, Kanchan; Palaninathan, Satheesh; Alcantara, Joanna Maria Ortiz

2008-03-31

The severe acute respiratory syndrome (SARS) coronavirus encodes several RNA-processing enzymes that are unusual for RNA viruses, including Nsp15 (nonstructural protein 15), a hexameric endoribonuclease that preferentially cleaves 3' of uridines. We solved the structure of a catalytically inactive mutant version of Nsp15, which was crystallized as a hexamer. The structure contains unreported flexibility in the active site of each subunit. Substitutions in the active site residues serine 293 and proline 343 allowed Nsp15 to cleave at cytidylate, whereas mutation of leucine 345 rendered Nsp15 able to cleave at purines as well as pyrimidines. Mutations that targeted the residues involvedmore » in subunit interactions generally resulted in the formation of catalytically inactive monomers. The RNA-binding residues were mapped by a method linking reversible cross-linking, RNA affinity purification, and peptide fingerprinting. Alanine substitution of several residues in the RNA-contacting portion of Nsp15 did not affect hexamer formation but decreased the affinity of RNA binding and reduced endonuclease activity. This suggests a model for Nsp15 hexamer interaction with RNA.« less

Role of non-metallic atoms in enhancing the catalytic activity of nickel-based compounds for hydrogen evolution reaction† †Electronic supplementary information (ESI) available: Experimental details, structure and morphology characterization, electrochemical characterizations, supplementary figures and data. See DOI: 10.1039/c7sc04851c

PubMed Central

Zheng, Xingqun; Peng, Lishan; Yang, Na; Yang, Yanjun; Li, Jing; Wang, Jianchuan

2018-01-01

The transition-metal compounds (MX) have gained wide attention as hydrogen evolution reaction (HER) electrocatalysts; however, the interaction between the non-metallic atom (X) and the metal atom (M) in MX, and the role of X in the enhanced catalytic activity of MX, are still ambiguous. In this work, we constructed a simple model [X/Ni(100)] to decipher the contribution of X towards enhancing the catalytic activity of NiX, which allows us to accurately predict the trend in HER catalytic activity of NiX based on the easily accessible physico-chemical characteristics of X. Theoretical calculations showed that the electronegativity (χX) and the principle quantum number (nX) of X are two important descriptors for evaluating and predicting the HER catalytic activity of NiX catalysts effectively. X atoms in the VIA group can enhance the HER activity of X/Ni(100) more significantly than those in the second period due to the large χX or nX. At a relatively low X coverage, the S/Ni(100) possesses the best HER activity among all of the discussed X/Ni(100) models, and the optimum surface S : Ni atomic ratio is about 22–33%. Further experiments demonstrated that the Ni–Ni3S2 catalyst with a surface S : Ni atomic ratio of 28.9% exhibits the best catalytic activity and lowest charge transfer resistance. The trend in catalytic activity of NiX with differing X offers a new possible strategy to exploit MX materials and design new active catalysts rationally. PMID:29675227

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

PubMed

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

2013-02-01

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

Computational QM/MM Study of the Reaction Mechanism of Human Glutathione S-Transferase A3-3

NASA Astrophysics Data System (ADS)

Calvaresi, Matteo; Stenta, Marco; Altoè, Piero; Bottoni, Andrea; Garavelli, Marco; Spinelli, Domenico

2007-12-01

Human Glutathione S-Transferase A3-3(hGSTA3-3) is the most efficient human steroid double-bond isomerase enzyme. It catalyzes the double bond isomerization of Δ5-androstene-3,17-dione (Δ5-AD) and Δ5-pregnene-3,20-dione (Δ5-PD). The isomerization products are the precursors of the steroid hormones testosterone and progesterone. We have carried out a QM/MM study to elucidate some interesting aspects of the enzyme catalytic mechanism. In particular, we have analyzed either a concerted or a stepwise reaction path. Moreover, we have attempted to rationalize the electrostatic effects on the catalytic activity of the residues surrounding the active site. Specifically, we have performed a "finger print" analysis to determine the electrostatic contribution of each aminoacid residue to the global electrostatic term, thus ranking the effect of the various aminoacids in the course of the reaction. In this way, we have highlighted the most important terms affecting the stabilization-destabilization of the enzyme.

Synthesis of ZnO/Zn nano photocatalyst using modified polysaccharides for photodegradation of dyes.

PubMed

Lin, Shi-Tsung; Thirumavalavan, Munusamy; Jiang, Ting-Yan; Lee, Jiunn-Fwu

2014-05-25

A complete set of experiments in two aspects of studies combining the various factors affecting both the preparation and photocatalytic activity of ZnO/Zn nanocomposite obtained using corn starch and cellulose (native and modified) as chelating agents for the photodegradation of methylene blue, and congo red was carried out and discussed. The resulting ZnO/Zn nanoparticles obtained using modified polysaccharides exhibited super catalytic capability. The ZnO/Zn nanoparticles possessed favored surface area (11.8443-15.7100m(2)/g) and pore size (12.3473-13.7453nm). The photocatalytic degradation of nano ZnO/Zn was directly proportional to the surface area of nano ZnO/Zn. Regardless of the dye pollutants, nano ZnO/Zn obtained using modified corn starch showed enhanced catalytic activity than that of cellulose and methylene blue had comparatively faster degradation rate. Our findings shed light on the optimization of both preparation conditions of photocatalysts and their photocatalytic experimental conditions. Copyright © 2014 Elsevier Ltd. All rights reserved.

Effect of Silica Particle Size on Texture, Structure, and Catalytic Performance of Cu/SiO2 Catalysts for Glycerol Hydrogenolysis

NASA Astrophysics Data System (ADS)

Qi, Ye Tong; Zhe, Chen Hong; Ning, Xiang

2018-03-01

The influences of carrier particle sizes of Cu/SiO2 catalysts for hydrogenolysis of glycerol were studied use mono-dispersed silica as models. Catalysts were prepared by precipitation method with the average size of the mono-dispersed silica supports varying of 10, 20, and 90 nm. Characterization of the catalysts show that the physical properties such as pore volume and BET surface area of the catalysts were largely affected by the carrier particle size of silica. However, the copper dispersion of the three samples were similar. XPS patterns show a difference in the chemical states of copper species, small carrier particle size induced formation of copper phyllosilicate, which benefits on the stability of copper species in reaction. The overall activity in the reaction of glycerol hydrogenolysis shows a correlation with the carrier particle size. The small carrier particles prevent the copper species from aggregation thus such catalysts exhibit good catalytic activity and stability.

High-density defects on PdAg nanowire networks as catalytic hot spots for efficient dehydrogenation of formic acid and reduction of nitrate.

PubMed

Liu, Hu; Yu, Yongsheng; Yang, Weiwei; Lei, Wenjuan; Gao, Manyi; Guo, Shaojun

2017-07-13

Controlling the surface defects of nanocrystals is a new way of tuning/boosting their catalytic properties. Herein, we report networked PdAg nanowires (NWs) with high-density defects as catalytic hot spots for efficient catalytic dehydrogenation of formic acid (FA) and catalytic reduction of nitrates. The networked PdAg NWs exhibit composition-dependent catalytic activity for the dehydrogenation reaction of FA without any additive, with Pd 5 Ag 5 NWs exhibiting the highest activity. They also show good durability, reflected by the retention of their initial activity during the dehydrogenation reaction of FA even after five cycles. Their initial TOF is 419 h -1 at 60 °C in water solution, much higher than those of the most Pd-based catalysts with a support. Moreover, they can efficiently reduce nitrates to alleviate nitrate pollution in water (conversion yield >99%). This strategy opens up a new green synthetic technique to design support-free heterogeneous catalysts with high-density defects as catalytic hot spots for efficient dehydrogenation catalysis of FA to meet the requirement of fuel cell applications and catalytic reduction of nitrates in water polluted with nitrates.

Preparation, Characterization, and Catalytic Activity of MoCo/USY Catalyst on Hydrodeoxygenation Reaction of Anisole

NASA Astrophysics Data System (ADS)

Nugrahaningtyas, K. D.; Suharbiansah, R. S. R.; Rahmawati, F.

2018-03-01

This research aims to prepare, characterize, and study the catalytic activity of Molybdenum (Mo) and Cobalt (Co) metal with supporting material Ultra Stable Y-Zeolite (USY), to produce catalysts with activity in hydrotreatment reaction and in order to eliminate impurities compounds that containing unwanted groups heteroatoms. The bimetallic catalysts MoCo/USY were prepared by wet impregnation method with weight variation of Co metal 0%, 2%, 4%, 6%, 8%, and Mo metal 8% (w/w), respectively. Activation method of the catalyst included calcination, oxidation, reduction and the crystallinity was characterized using X-ray diffraction (XRD), the acidity of the catalyst was analyzed using Fourier Transform Infrared Spectroscopy (FT-IR) and gravimetry method, minerals present in the catalyst was analyzed using X-Ray Fluorescence (XRF), and surface of the catalyst was analyzed using Surface Area Analyzer (SAA). Catalytic activity test (benzene yield product) of MoCo/USY on hydrodeoxigenation reaction of anisole aimed to determine the effect of Mo-Co/USY for catalytic activity in the reaction hydrodeoxigenation (HDO) anisole. Based on characterization and test of catalytic activity, it is known that catalytic of MoCo/USY 2% (catalyst B) shows best activities with acidity of 10.209 mmol/g, specific area of catalyst of 426.295 m2/g, pore average of 14.135 Å, total pore volume 0.318 cc/g, and total yield of HDO products 6.06%.

Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Manhua; Wang, Xiang; Yeom, Younghoon

A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase id dispersed.

Gas phase heterogeneous catalytic oxidation of alkanes to aliphatic ketones and/or other oxygenates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Manhua; Wang, Xiang; Yeom, Younghoon

A catalyst, its method of preparation and its use for producing aliphatic ketones by subjecting alkanes C.sub.3 to C.sub.9 to a gas phase catalytic oxidation in the presence of air or oxygen, and, optionally, steam and/or one or more diluting gases. The catalyst comprises a catalytically active mixed metal oxide phase and a suitable support material onto and/or into which the active catalytic phase is dispersed.

Catalytic activity of certain antibodies as a potential tool for drug synthesis and for directed prodrug therapies.

PubMed

Wójcik, T; Kieć-Kononowicz, K

2008-01-01

Catalytic activity of certain antibodies was proposed by Linus Pauling for the very first time more than six decades ago. Since then few examples of catalytic antibodies (abzymes) were found in human organism. From late 80's many synthetic abzymes were obtained after immunization by Transition State Analogs (TSA). Another approach is based on functional mimicry of antibody to an active site of an enzyme. Detection of an abzymatic activity requires special immunoassays. This unique strategy can be employed for new methods of drug synthesis, as well as for in vivo therapies. Catalytic antibodies seem to be a promising tool for therapeutic purposes, because of their specifity and stereoselectivity.

Enhanced catalytic activity without the use of an external light source using microwave-synthesized CuO nanopetals

PubMed Central

Bajaj, Sonal; Nayak, Arpan Kumar; Pradhan, Debabrata; Tekade, Pradip

2017-01-01

We report enhanced catalytic activity of CuO nanopetals synthesized by microwave-assisted wet chemical synthesis. The catalytic reaction of CuO nanopetals and H2O2 was studied with the application of external light source and also under dark conditions for the degradation of the hazardous dye methylene blue. The CuO nanopetals showed significant catalytic activity for the fast degradation of methylene blue and rhodamine B (RhB) under dark conditions, without the application of an external light source. This increased catalytic activity was attributed to the co-operative role of H2O2 and the large specific surface area (≈40 m2·g−1) of the nanopetals. We propose a detail mechanism for this fast degradation. A separate study of the effect of different H2O2 concentrations for the degradation of methylene blue under dark conditions is also illustrated. PMID:28685117

Photonic Activation of Plasminogen Induced by Low Dose UVB

PubMed Central

Correia, Manuel; Snabe, Torben; Thiagarajan, Viruthachalam; Petersen, Steffen Bjørn; Campos, Sara R. R.; Baptista, António M.; Neves-Petersen, Maria Teresa

2015-01-01

Activation of plasminogen to its active form plasmin is essential for several key mechanisms, including the dissolution of blood clots. Activation occurs naturally via enzymatic proteolysis. We report that activation can be achieved with 280 nm light. A 2.6 fold increase in proteolytic activity was observed after 10 min illumination of human plasminogen. Irradiance levels used are in the same order of magnitude of the UVB solar irradiance. Activation is correlated with light induced disruption of disulphide bridges upon UVB excitation of the aromatic residues and with the formation of photochemical products, e.g. dityrosine and N-formylkynurenine. Most of the protein fold is maintained after 10 min illumination since no major changes are observed in the near-UV CD spectrum. Far-UV CD shows loss of secondary structure after illumination (33.4% signal loss at 206 nm). Thermal unfolding CD studies show that plasminogen retains a native like cooperative transition at ~70 ºC after UV-illumination. We propose that UVB activation of plasminogen occurs upon photo-cleavage of a functional allosteric disulphide bond, Cys737-Cys765, located in the catalytic domain and in van der Waals contact with Trp761 (4.3 Å). Such proximity makes its disruption very likely, which may occur upon electron transfer from excited Trp761. Reduction of Cys737-Cys765 will result in likely conformational changes in the catalytic site. Molecular dynamics simulations reveal that reduction of Cys737-Cys765 in plasminogen leads to an increase of the fluctuations of loop 760–765, the S1-entrance frame located close to the active site. These fluctuations affect the range of solvent exposure of the catalytic triad, particularly of Asp646 and Ser74, which acquire an exposure profile similar to the values in plasmin. The presented photonic mechanism of plasminogen activation has the potential to be used in clinical applications, possibly together with other enzymatic treatments for the elimination of blood clots. PMID:25635856

Preparation of PdCu Alloy Nanocatalysts for Nitrate Hydrogenation and Carbon Monoxide Oxidation

DOE PAGES

Cai, Fan; Yang, Lefu; Shan, Shiyao; ...

2016-06-30

Alloying Pd with Cu is important for catalytic reactions such as denitrification reaction and CO oxidation reaction, but understanding of the catalyst preparation and its correlation with the catalyst’s activity and selectivity remains elusive. Herein, we report the results of investigations of the preparation of PdCu alloy nanocatalysts using different methods and the catalytic properties of the catalysts in catalytic denitrification reaction and CO oxidation reaction. PdCu alloy nanocatalysts were prepared by conventional dry impregnation method and ligand-capping based wet chemical synthesis method, and subsequent thermochemical activation as well. The alloying characteristics depend on the bimetallic composition. PdCu/Al 2O 3more » with a Pd/Cu ratio of 50:50 was shown to exhibit an optimized hydrogenation activity for the catalytic denitrification reaction. The catalytic activity of the PdCu catalysts was shown to be highly dependent on the support, as evidenced by the observation of an enhanced catalytic activity for CO oxidation reaction using TiO 2 and CeO 2 supports with high oxygen storage capacity. Lastly, we discussed the implications of the results to the refinement of the preparation of the alloy nanocatalysts.« less

Fructose-1,6-bisphosphate aldolase (class II) is the primary site of nickel toxicity in Escherichia coli.

PubMed

Macomber, Lee; Elsey, Scott P; Hausinger, Robert P

2011-12-01

Nickel is toxic to all forms of life, but the mechanisms of cell damage are unknown. Indeed, environmentally relevant nickel levels (8 µM) inhibit wild-type Escherichia coli growth on glucose minimal medium. The same concentration of nickel also inhibits growth on fructose, but not succinate, lactate or glycerol; these results suggest that fructose-1,6-bisphosphate aldolase (FbaA) is a target of nickel toxicity. Cells stressed by 8 µM Ni(II) for 20 min lost 75% of their FbaA activity, demonstrating that FbaA is inactivated during nickel stress. Furthermore, overexpression of fbaA restored growth of an rcnA mutant in glucose minimal medium supplemented with 4 µM Ni(II), thus confirming that FbaA is a primary target of nickel toxicity. This class II aldolase has an active site zinc and a non-catalytic zinc nearby. Purified FbaA lost 80 % of its activity within 2 min when challenged with 8 µM Ni(II). Nickel-challenged FbaA lost 0.8 zinc and gained 0.8 nickel per inactivated monomer. FbaA mutants (D144A and E174A) affecting the non-catalytic zinc were resistant to nickel inhibition. These results define the primary site of nickel toxicity in E. coli as the class II aldolase FbaA through binding to the non-catalytic zinc site. © 2011 Blackwell Publishing Ltd.

Poliovirus Replication Requires the N-terminus but not the Catalytic Sec7 Domain of ArfGEF GBF1

PubMed Central

Belov, George A.; Kovtunovych, Gennadiy; Jackson, Catherine L.; Ehrenfeld, Ellie

2010-01-01

Viruses are intracellular parasites whose reproduction relies on factors provided by the host. The cellular protein GBF1 is critical for poliovirus replication. Here we show that the contribution of GBF1 to virus replication is different from its known activities in uninfected cells. Normally GBF1 activates the Arf GTPases necessary for formation of COPI transport vesicles. GBF1 function is modulated by p115 and Rab1b. However, in polio-infected cells, p115 is degraded and neither p115 nor Rab1b knock-down affects virus replication. Poliovirus infection is very sensitive to BFA, an inhibitor of Arf activation by GBF1. BFA targets the catalytic Sec7 domain of GBF1. Nevertheless the BFA block of polio replication is rescued by expression of only the N-terminal region of GBF1 lacking the Sec7 domain. Replication of BFA-resistant poliovirus in the presence of BFA is uncoupled from Arf activation but is dependent on GBF1. Thus the function(s) of this protein essential for viral replication can be separated from those required for cellular metabolism. PMID:20497182

Electronic states of carbon alloy catalysts and nitrogen substituent effects on catalytic activity

NASA Astrophysics Data System (ADS)

Hata, Tomoyuki; Ushiyama, Hiroshi; Yamashita, Koichi

2013-03-01

In recent years, Carbon Alloy Catalysts (CACs) are attracting attention as a candidate for non-platinum-based cathode catalysts in fuel cells. Oxygen reduction reactions at the cathode are divided into two elementary processes, electron transfer and oxygen adsorption. The electron transfer reaction is the rate-determining, and by comparison of energy levels, catalytic activity can be evaluated quantitatively. On the other hand, to begin with, adsorption mechanism is obscure. The purpose of this study is to understand the effect of nitrogen substitution and oxygen adsorption mechanism, by first-principle electronic structure calculations for nitrogen substituted models. To reproduce the elementary processes of oxygen adsorption, we assumed that the initial structures are formed based on the Pauling model, a CACs model and nitrogen substituted CACs models in which various points are replaced with nitrogen. When we try to focus only on the DOS peaks of oxygen, in some substituted model that has high adsorption activity, a characteristic partial occupancy state was found. We conclude that this state will affect the adsorption activity, and discuss on why partially occupied states appear with simplification by using an orbital correlation diagram.

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.

Probing the catalytic functions of Bub1 kinase using the small molecule inhibitors BAY-320 and BAY-524

PubMed Central

Baron, Anna P; von Schubert, Conrad; Cubizolles, Fabien; Siemeister, Gerhard; Hitchcock, Marion; Mengel, Anne; Schröder, Jens; Fernández-Montalván, Amaury; von Nussbaum, Franz; Mumberg, Dominik; Nigg, Erich A

2016-01-01

The kinase Bub1 functions in the spindle assembly checkpoint (SAC) and in chromosome congression, but the role of its catalytic activity remains controversial. Here, we use two novel Bub1 inhibitors, BAY-320 and BAY-524, to demonstrate potent Bub1 kinase inhibition both in vitro and in intact cells. Then, we compared the cellular phenotypes of Bub1 kinase inhibition in HeLa and RPE1 cells with those of protein depletion, indicative of catalytic or scaffolding functions, respectively. Bub1 inhibition affected chromosome association of Shugoshin and the chromosomal passenger complex (CPC), without abolishing global Aurora B function. Consequently, inhibition of Bub1 kinase impaired chromosome arm resolution but exerted only minor effects on mitotic progression or SAC function. Importantly, BAY-320 and BAY-524 treatment sensitized cells to low doses of Paclitaxel, impairing both chromosome segregation and cell proliferation. These findings are relevant to our understanding of Bub1 kinase function and the prospects of targeting Bub1 for therapeutic applications. DOI: http://dx.doi.org/10.7554/eLife.12187.001 PMID:26885717

Thermal Catalytic Oxidation of Airborne Contaminants by a Reactor Using Ultra-Short Channel Length, Monolithic Catalyst Substrates

NASA Technical Reports Server (NTRS)

Perry, J. L.; Tomes, K. M.; Tatara, J. D.

2005-01-01

Contaminated air, whether in a crewed spacecraft cabin or terrestrial work and living spaces, is a pervasive problem affecting human health, performance, and well being. The need for highly effective, economical air quality processes spans a wide range of terrestrial and space flight applications. Typically, air quality control processes rely on absorption-based processes. Most industrial packed-bed adsorption processes use activated carbon. Once saturated, the carbon is either dumped or regenerated. In either case, the dumped carbon and concentrated waste streams constitute a hazardous waste that must be handled safely while minimizing environmental impact. Thermal catalytic oxidation processes designed to address waste handling issues are moving to the forefront of cleaner air quality control and process gas decontamination processes. Careful consideration in designing the catalyst substrate and reactor can lead to more complete contaminant destruction and poisoning resistance. Maintenance improvements leading to reduced waste handling and process downtime can also be realized. Performance of a prototype thermal catalytic reaction based on ultra-short waste channel, monolith catalyst substrate design, under a variety of process flow and contaminant loading conditions, is discussed.

Metal-Induced Stabilization and Activation of Plasmid Replication Initiator RepB

PubMed Central

Ruiz-Masó, José A.; Bordanaba-Ruiseco, Lorena; Sanz, Marta; Menéndez, Margarita; del Solar, Gloria

2016-01-01

Initiation of plasmid rolling circle replication (RCR) is catalyzed by a plasmid-encoded Rep protein that performs a Tyr- and metal-dependent site-specific cleavage of one DNA strand within the double-strand origin (dso) of replication. The crystal structure of RepB, the initiator protein of the streptococcal plasmid pMV158, constitutes the first example of a Rep protein structure from RCR plasmids. It forms a toroidal homohexameric ring where each RepB protomer consists of two domains: the C-terminal domain involved in oligomerization and the N-terminal domain containing the DNA-binding and endonuclease activities. Binding of Mn2+ to the active site is essential for the catalytic activity of RepB. In this work, we have studied the effects of metal binding on the structure and thermostability of full-length hexameric RepB and each of its separate domains by using different biophysical approaches. The analysis of the temperature-induced changes in RepB shows that the first thermal transition, which occurs at a range of temperatures physiologically relevant for the pMV158 pneumococcal host, represents an irreversible conformational change that affects the secondary and tertiary structure of the protein, which becomes prone to self-associate. This transition, which is also shown to result in loss of DNA binding capacity and catalytic activity of RepB, is confined to its N-terminal domain. Mn2+ protects the protein from undergoing this detrimental conformational change and the observed protection correlates well with the high-affinity binding of the cation to the active site, as substituting one of the metal-ligands at this site impairs both the protein affinity for Mn2+and the Mn2+-driven thermostabilization effect. The level of catalytic activity of the protein, especially in the case of full-length RepB, cannot be explained based only on the high-affinity binding of Mn2+ at the active site and suggests the existence of additional, lower-affinity metal binding site(s), missing in the separate catalytic domain, that must also be saturated for maximal activity. The molecular bases of the thermostabilizing effect of Mn2+ on the N-terminal domain of the protein as well as the potential location of additional metal binding sites in the entire RepB are discussed. PMID:27709114

Direct measurement of the protein response to an electrostatic perturbation that mimics the catalytic cycle in ketosteroid isomerase.

PubMed

Jha, Santosh Kumar; Ji, Minbiao; Gaffney, Kelly J; Boxer, Steven G

2011-10-04

Understanding how electric fields and their fluctuations in the active site of enzymes affect efficient catalysis represents a critical objective of biochemical research. We have directly measured the dynamics of the electric field in the active site of a highly proficient enzyme, Δ(5)-3-ketosteroid isomerase (KSI), in response to a sudden electrostatic perturbation that simulates the charge displacement that occurs along the KSI catalytic reaction coordinate. Photoexcitation of a fluorescent analog (coumarin 183) of the reaction intermediate mimics the change in charge distribution that occurs between the reactant and intermediate state in the steroid substrate of KSI. We measured the electrostatic response and angular dynamics of four probe dipoles in the enzyme active site by monitoring the time-resolved changes in the vibrational absorbance (IR) spectrum of a spectator thiocyanate moiety (a quantitative sensor of changes in electric field) placed at four different locations in and around the active site, using polarization-dependent transient vibrational Stark spectroscopy. The four different dipoles in the active site remain immobile and do not align to the changes in the substrate electric field. These results indicate that the active site of KSI is preorganized with respect to functionally relevant changes in electric fields.

Direct measurement of the protein response to an electrostatic perturbation that mimics the catalytic cycle in ketosteroid isomerase

PubMed Central

Jha, Santosh Kumar; Ji, Minbiao; Gaffney, Kelly J.; Boxer, Steven G.

2011-01-01

Understanding how electric fields and their fluctuations in the active site of enzymes affect efficient catalysis represents a critical objective of biochemical research. We have directly measured the dynamics of the electric field in the active site of a highly proficient enzyme, Δ5-3-ketosteroid isomerase (KSI), in response to a sudden electrostatic perturbation that simulates the charge displacement that occurs along the KSI catalytic reaction coordinate. Photoexcitation of a fluorescent analog (coumarin 183) of the reaction intermediate mimics the change in charge distribution that occurs between the reactant and intermediate state in the steroid substrate of KSI. We measured the electrostatic response and angular dynamics of four probe dipoles in the enzyme active site by monitoring the time-resolved changes in the vibrational absorbance (IR) spectrum of a spectator thiocyanate moiety (a quantitative sensor of changes in electric field) placed at four different locations in and around the active site, using polarization-dependent transient vibrational Stark spectroscopy. The four different dipoles in the active site remain immobile and do not align to the changes in the substrate electric field. These results indicate that the active site of KSI is preorganized with respect to functionally relevant changes in electric fields. PMID:21949360

Simultaneous probing of bulk liquid phase and catalytic gas-liquid-solid interface under working conditions using attenuated total reflection infrared spectroscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meemken, Fabian; Müller, Philipp; Hungerbühler, Konrad

Design and performance of a reactor set-up for attenuated total reflection infrared (ATR-IR) spectroscopy suitable for simultaneous reaction monitoring of bulk liquid and catalytic solid-liquid-gas interfaces under working conditions are presented. As advancement of in situ spectroscopy an operando methodology for gas-liquid-solid reaction monitoring was developed that simultaneously combines catalytic activity and molecular level detection at the catalytically active site of the same sample. Semi-batch reactor conditions are achieved with the analytical set-up by implementing the ATR-IR flow-through cell in a recycle reactor system and integrating a specifically designed gas feeding system coupled with a bubble trap. By the usemore » of only one spectrometer the design of the new ATR-IR reactor cell allows for simultaneous detection of the bulk liquid and the catalytic interface during the working reaction. Holding two internal reflection elements (IRE) the sample compartments of the horizontally movable cell are consecutively flushed with reaction solution and pneumatically actuated, rapid switching of the cell (<1 s) enables to quasi simultaneously follow the heterogeneously catalysed reaction at the catalytic interface on a catalyst-coated IRE and in the bulk liquid on a blank IRE. For a complex heterogeneous reaction, the asymmetric hydrogenation of 2,2,2-trifluoroacetophenone on chirally modified Pt catalyst the elucidation of catalytic activity/enantioselectivity coupled with simultaneous monitoring of the catalytic solid-liquid-gas interface is shown. Both catalytic activity and enantioselectivity are strongly dependent on the experimental conditions. The opportunity to gain improved understanding by coupling measurements of catalytic performance and spectroscopic detection is presented. In addition, the applicability of modulation excitation spectroscopy and phase-sensitive detection are demonstrated.« less

Magnetic cobaltic nanoparticle-anchored carbon nanocomposite derived from cobalt-dipicolinic acid coordination polymer: An enhanced catalyst for environmental oxidative and reductive reactions.

PubMed

Wu, Chang-Hsun; Lin, Jyun-Ting; Lin, Kun-Yi Andrew

2018-05-01

Direct carbonization of cobalt complexes represents as a convenient approach to prepare magnetic carbon/cobalt nanocomposites (MCCNs) as heterogeneous environmental catalysts. However, most of MCCNs derived from consist of sheet-like carbon matrices with very sparse cobaltic nanoparticles (NPs), making them exhibit relatively low catalytic activities, porosity and magnetism. In this study, dipicolinic acid (DPA) is selected to prepare a 3-dimensional cobalt coordination polymer (CoDPA). MCCN derived from CoDPA can consist of a porous carbon matrix embedded with highly-dense Co 0 and Co 3 O 4 NPs. This magnetic Co 0 /Co 3 O 4 NP-anchored carbon composite (MCNC) appears as a promising heterogeneous catalyst for oxidative and reductive environmental catalytic reactions. As peroxymonosulfate (PMS) activation is selected as a model catalytic oxidative reaction, MCNC exhibits a much higher catalytic activity than Co 3 O 4 , a benchmark catalyst for PMS activation. The reductive catalytic activity of MCNC is demonstrated through 4-nitrophenol (4-NP) reduction in the presence of NaBH 4 . MCNC could rapidly react with NaBH 4 to generate H 2 for hydrogenation of 4-NP to 4-aminophenol (4-AP). In comparison with other precious metallic catalysts, MCNC also shows a relatively high catalytic activity. These results indicate that MCNC is a conveniently prepared and highly effective and stable carbon-supported cobaltic heterogeneous catalyst for versatile environmental catalytic applications. Copyright © 2018 Elsevier Inc. All rights reserved.

Investigating the effects of alkali metal Na addition on catalytic activity of HZSM-5 for methyl mercaptan elimination

NASA Astrophysics Data System (ADS)

Yu, Jie; He, Dedong; Chen, Dingkai; Liu, Jiangping; Lu, Jichang; Liu, Feng; Liu, Pan; Zhao, Yutong; Xu, Zhizhi; Luo, Yongming

2017-10-01

Na-modified HZSM-5 catalysts with different Na loading amounts were prepared by incipient-wetness impregnation method and their catalytic activities for methyl mercaptan catalytic elimination were analyzed. XRD, N2 adsorption-desorption, NH3-TPD, CO2-TPD and FT-IR measurements were carried out to investigate the effects of modification of alkali metal Na on the physicochemical properties of the HZSM-5 zeolite catalyst. Research results illustrated that the introduction of alkali metal Na can improve catalytic activity for CH3SH catalytic elimination. CH3SH can be almost completely converted over 3%-Na/HZSM-5 at 450 °C compared to pure HZSM-5 at 600 °C based on our experimental results and the results from previous research. The improved catalytic activity could be attributed to the regulated acid-base properties of the HZSM-5 catalysts by doping with alkali metal Na. High alkali concentration treatment, however, may destroy the framework structure of the catalyst sample, thus causing the poor stability performance of the obtained catalyst.

Constitutive production of catalytic antibodies to a Staphylococcus aureus virulence factor and effect of infection.

PubMed

Brown, Eric L; Nishiyama, Yasuhiro; Dunkle, Jesse W; Aggarwal, Shreya; Planque, Stephanie; Watanabe, Kenji; Csencsits-Smith, Keri; Bowden, M Gabriela; Kaplan, Sheldon L; Paul, Sudhir

2012-03-23

Antibodies that recognize microbial B lymphocyte superantigenic epitopes are produced constitutively with no requirement for adaptive immune maturation. We report cleavage of the Staphylococcus aureus virulence factor extracellular fibrinogen-binding protein (Efb) by catalytic antibodies produced with no exposure to the bacterium and reduction of the catalytic antibody activity following infection. IgG catalytic antibodies that specifically hydrolyzed Efb via a nucleophilic catalytic mechanism were found in the blood of healthy humans and aseptic mice free of S. aureus infection. IgG hydrolyzed peptide bonds on the C-terminal side of basic amino acids, including a bond located within the C3b-binding domain of Efb. Efb digested with the IgG lost its ability to bind C3b and inhibit complement-dependent antibody-mediated red blood cell lysis. In addition to catalysis, the IgG expressed saturable Efb binding activity. IgG from S. aureus-infected mice displayed reduced Efb cleaving activity and increased Efb binding activity compared with uninfected controls, suggesting differing effects of the infection on the antibody subsets responsible for the two activities. IgG from children hospitalized for S. aureus infection also displayed reduced Efb cleavage compared with healthy children. These data suggest a potential defense function for constitutively produced catalytic antibodies to a putative superantigenic site of Efb, but an adaptive catalytic response appears to be proscribed.

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.

Structural Basis for the Catalytic Activity of Human Serine/Threonine Protein Phosphatase type 5 (PP5)

NASA Technical Reports Server (NTRS)

Swingle, Mark R.; Ciszak, Ewa M.; Honkanen, Richard E.

2004-01-01

Serine/threonine protein phosphatase-5 (PP5) is a member of the PPP-gene family of protein phosphatases that is widely expressed in mammalian tissues and is highly conserved among eukaryotes. PP5 associates with several proteins that affect signal transduction networks, including the glucocorticoid receptor (GR)-heat shock protein-90 (Hsp90)-heterocomplex, the CDC16 and CDC27 subunits of the anaphase-promoting complex, elF2alpha kinase, the A subunit of PP2A, the G12-alpha / G13-alpha subunits of heterotrimeric G proteins and DNA-PK. The catalytic domain of PP5 (PP5c) shares 35-45% sequence identity with the catalytic domains of other PPP-phosphatases, including protein phosphatase-1 (PP1), -2A (PP2A), -2B / calcineurin (PP2B), -4 (PP4), -6 (PP6), and -7 (PP7). Like PP1, PP2A and PP4, PP5 is also sensitive to inhibition by okadaic acid, microcystin, cantharidin, tautomycin, and calyculin A. Here we report the crystal structure of the PP5 catalytic domain (PP5c) at a resolution of 1.6 angstroms. From this structure we propose a mechanism for PP5-mediated hydrolysis of phosphoprotein substrates, which requires the precise positioning of two metal ions within a conserved Asp(sup 271)-M(sub 1):M(sub 2)-W(sup 1)-His(sup 304)-Asp(sup 274) catalytic motif. The structure of PP5c provides a possible structural basis for explaining the exceptional catalytic proficiency of protein phosphatases, which are among the most powerful known catalysts. Resolution of the entire C-terminus revealed a novel subdomain, and the structure of the PP5c should also aid development of type-specific inhibitors.

Investigation of hybrid plasma-catalytic removal of acetone over CuO/γ-Al2O3 catalysts using response surface method.

PubMed

Zhu, Xinbo; Tu, Xin; Mei, Danhua; Zheng, Chenghang; Zhou, Jinsong; Gao, Xiang; Luo, Zhongyang; Ni, Mingjiang; Cen, Kefa

2016-07-01

In this work, plasma-catalytic removal of low concentrations of acetone over CuO/γ-Al2O3 catalysts was carried out in a cylindrical dielectric barrier discharge (DBD) reactor. The combination of plasma and the CuO/γ-Al2O3 catalysts significantly enhanced the removal efficiency of acetone compared to the plasma process using the pure γ-Al2O3 support, with the 5.0 wt% CuO/γ-Al2O3 catalyst exhibiting the best acetone removal efficiency of 67.9%. Catalyst characterization was carried out to understand the effect the catalyst properties had on the activity of the CuO/γ-Al2O3 catalysts in the plasma-catalytic reaction. The results indicated that the formation of surface oxygen species on the surface of the catalysts was crucial for the oxidation of acetone in the plasma-catalytic reaction. The effects that various operating parameters (discharge power, flow rate and initial concentration of acetone) and the interactions between these parameters had on the performance of the plasma-catalytic removal of acetone over the 5.0 wt% CuO/γ-Al2O3 catalyst were investigated using central composite design (CCD). The significance of the independent variables and their interactions were evaluated by means of the Analysis of Variance (ANOVA). The results showed that the gas flow rate was the most significant factor affecting the removal efficiency of acetone, whilst the initial concentration of acetone played the most important role in determining the energy efficiency of the plasma-catalytic process. Copyright © 2016 Elsevier Ltd. All rights reserved.

The DNA Maturation Domain of gpA, the DNA Packaging Motor Protein of Bacteriophage Lambda, Contains an ATPase Site Associated with Endonuclease Activity

PubMed Central

Ortega, Marcos E.; Gaussier, Helene; Catalano, Carlos E.

2007-01-01

Summary Terminase enzymes are common to double-stranded DNA (dsDNA) viruses and are responsible for packaging viral DNA into the confines of an empty capsid shell. In bacteriophage lambda the catalytic terminase subunit is gpA, which is responsible for maturation of the genome end prior to packaging and subsequent translocation of the matured DNA into the capsid. DNA packaging requires an ATPase catalytic site situated in the N-terminus of the protein. A second ATPase catalytic site associated with the DNA maturation activities of the protein has been proposed; however, direct demonstration of this putative second site is lacking. Here we describe biochemical studies that define protease-resistant peptides of gpA and expression of these putative domains in E. coli. Biochemical characterization of gpA-ΔN179, a construct in which the N-terminal 179 residues of gpA have been deleted, indicates that this protein encompasses the DNA maturation domain of gpA. The construct is folded, soluble and possesses an ATP-dependent nuclease activity. Moreover, the construct binds and hydrolyzes ATP despite the fact that the DNA packaging ATPase site in the N-terminus of gpA has been deleted. Mutation of lysine 497, which alters the conserved lysine in a predicted Walker A “P-loop” sequence, does not affect ATP binding but severely impairs ATP hydrolysis. Further, this mutation abrogates the ATP-dependent nuclease activity of the protein. These studies provide direct evidence for the elusive nucleotide-binding site in gpA that is directly associated with the DNA maturation activity of the protein. The implications of these results with respect to the two roles of the terminase holoenzyme – DNA maturation and DNA packaging – are discussed. PMID:17870092

Pressure- and heat-induced inactivation of butyrylcholinesterase: evidence for multiple intermediates and the remnant inactivation process.

PubMed Central

Weingand-Ziade, A; Ribes, F; Renault, F; Masson, P

2001-01-01

The inactivation process of native (N) human butyrylcholinesterase (BuChE) by pressure and/or heat was found to be multi-step. It led to irreversible formation of an active intermediate (I) state and a denatured state. This series-inactivation process was described by expanding the Lumry-Eyring [Lumry, R. and Eyring, H. (1954) J. Phys. Chem. 58, 110-120] model. The intermediate state (I) was found to have a K(m) identical with that of the native state and a turnover rate (k(cat)) twofold higher than that of the native state with butyrylthiocholine as the substrate. The increased catalytic efficiency (k(cat)/K(m)) of I can be explained by a conformational change in the active-site gorge and/or restructuring of the water-molecule network in the active-site pocket, making the catalytic steps faster. However, a pressure/heat-induced covalent modification of native BuChE, affecting the catalytic machinery, cannot be ruled out. The inactivation process of BuChE induced by the combined action of pressure and heat was found to continue after interruption of pressure/temperature treatment. This secondary inactivation process was termed 'remnant inactivation'. We hypothesized that N and I were in equilibrium with populated metastable N' and I' states. The N' and I' states can either return to the active forms, N and I, or develop into inactive forms, N(')(in) and I(')(in). Both active N' and I' intermediate states displayed different rates of remnant inactivation depending on the pressure and temperature pretreatments and on the storage temperature. A first-order deactivation model describing the kinetics of the remnant inactivation of BuChE is proposed. PMID:11368776

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bae, Brian; Nayak, Dhananjaya; Ray, Ananya

RNA polymerase inhibitors like the CBR class that target the enzyme’s complex catalytic center are attractive leads for new antimicrobials. The catalysis by RNA polymerase involves multiple rearrangements of bridge helix, trigger loop, and active-center side chains that isomerize the triphosphate of bound NTP and two Mg 2+ ions from a preinsertion state to a reactive configuration. CBR inhibitors target a crevice between the N-terminal portion of the bridge helix and a surrounding cap region within which the bridge helix is thought to rearrange during the nucleotide addition cycle. Here, we report crystal structures of CBR inhibitor/Escherichia coli RNA polymerasemore » complexes as well as biochemical tests that establish two distinct effects of the inhibitors on the RNA polymerase catalytic site. One effect involves inhibition of trigger-loop folding via the F loop in the cap, which affects both nucleotide addition and hydrolysis of 3'-terminal dinucleotides in certain backtracked complexes. The second effect is trigger-loop independent, affects only nucleotide addition and pyrophosphorolysis, and may involve inhibition of bridge-helix movements that facilitate reactive triphosphate alignment.« less

HIgh Temperature Photocatalysis over Semiconductors

NASA Astrophysics Data System (ADS)

Westrich, Thomas A.

Due in large part to in prevalence of solar energy, increasing demand of energy production (from all sources), and the uncertain future of petroleum energy feedstocks, solar energy harvesting and other photochemical systems will play a major role in the developing energy market. This dissertation focuses on a novel photochemical reaction process: high temperature photocatalysis (i.e., photocatalysis conducted above ambient temperatures, T ≥ 100°C). The overarching hypothesis of this process is that photo-generated charge carriers are able to constructively participate in thermo-catalytic chemical reactions, thereby increasing catalytic rates at one temperature, or maintaining catalytic rates at lower temperatures. The photocatalytic oxidation of carbon deposits in an operational hydrocarbon reformer is one envisioned application of high temperature photocatalysis. Carbon build-up during hydrocarbon reforming results in catalyst deactivation, in the worst cases, this was shown to happen in a period of minutes with a liquid hydrocarbon. In the presence of steam, oxygen, and above-ambient temperatures, carbonaceous deposits were photocatalytically oxidized over very long periods (t ≥ 24 hours). This initial experiment exemplified the necessity of a fundamental assessment of high temperature photocatalytic activity. Fundamental understanding of the mechanisms that affect photocatalytic activity as a function of temperatures was achieved using an ethylene photocatalytic oxidation probe reaction. Maximum ethylene photocatalytic oxidation rates were observed between 100 °C and 200 °C; the maximum photocatalytic rates were approximately a factor of 2 larger than photocatalytic rates at ambient temperatures. The loss of photocatalytic activity at temperatures above 200 °C is due to a non-radiative multi-phonon recombination mechanism. Further, it was shown that the fundamental rate of recombination (as a function of temperature) can be effectively modeled as a temperature-dependent quantum efficiency term, and is directly driven by bulk photocatalyst crystal parameters: maximum phonon energy and the number of phonons allowed per unit cell. This analysis extends to multiple photocatalysts and can explain experimental observations of photocatalytic oxidation rates with varied reactant concentrations. Lastly, this dissertation applies this knowledge to a thermo-catalytic reaction (CO-oxidation) using a Au/TiO 2 catalyst. The combined photo/thereto-catalytic reaction showed a 10-25% increase in CO conversion during a temperature programmed reaction experiment.

Selenium/Tellurium-Containing Hyperbranched Polymers: Effect of Molecular Weight and Degree of Branching on Glutathione Peroxidase-Like Activity.

PubMed

Thomas, Joice; Dong, Zeyuan; Dehaen, Wim; Smet, Mario

2012-12-21

A series of novel hyperbranched polyselenides and polytellurides with multiple catalytic sites at the branching units has been synthesized via the polycondensation of A2 + B3 monomers. The GPx-like activities of these polymer mimics were assessed and it was found that the polytellurides showed higher GPx-like activities than the corresponding polyselenides. Interestingly, the polymers with higher molecular weights and degree of branching (DB) showed higher GPx-like activities than the analogous lower molecular weight polymer. The enhancement in the catalytical activity of the hyperbranched polymers with increasing molecular weight affirmed the importance of the incorporation of multiple catalytic groups in the macromolecule which increases the local concentration of catalytic sites. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Perovskite-type catalytic materials for environmental applications.

PubMed

Labhasetwar, Nitin; Saravanan, Govindachetty; Kumar Megarajan, Suresh; Manwar, Nilesh; Khobragade, Rohini; Doggali, Pradeep; Grasset, Fabien

2015-06-01

Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N 2 O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications.

Perovskite-type catalytic materials for environmental applications

PubMed Central

Labhasetwar, Nitin; Saravanan, Govindachetty; Kumar Megarajan, Suresh; Manwar, Nilesh; Khobragade, Rohini; Doggali, Pradeep; Grasset, Fabien

2015-01-01

Perovskites are mixed-metal oxides that are attracting much scientific and application interest owing to their low price, adaptability, and thermal stability, which often depend on bulk and surface characteristics. These materials have been extensively explored for their catalytic, electrical, magnetic, and optical properties. They are promising candidates for the photocatalytic splitting of water and have also been extensively studied for environmental catalysis applications. Oxygen and cation non-stoichiometry can be tailored in a large number of perovskite compositions to achieve the desired catalytic activity, including multifunctional catalytic properties. Despite the extensive uses, the commercial success for this class of perovskite-based catalytic materials has not been achieved for vehicle exhaust emission control or for many other environmental applications. With recent advances in synthesis techniques, including the preparation of supported perovskites, and increasing understanding of promoted substitute perovskite-type materials, there is a growing interest in applied studies of perovskite-type catalytic materials. We have studied a number of perovskites based on Co, Mn, Ru, and Fe and their substituted compositions for their catalytic activity in terms of diesel soot oxidation, three-way catalysis, N2O decomposition, low-temperature CO oxidation, oxidation of volatile organic compounds, etc. The enhanced catalytic activity of these materials is attributed mainly to their altered redox properties, the promotional effect of co-ions, and the increased exposure of catalytically active transition metals in certain preparations. The recent lowering of sulfur content in fuel and concerns over the cost and availability of precious metals are responsible for renewed interest in perovskite-type catalysts for environmental applications. PMID:27877813

Molecular Basis of Gain-of-Function LEOPARD Syndrome-Associated SHP2 Mutations

PubMed Central

2015-01-01

The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 2 (SHP2) is a critical signal transducer downstream of growth factors that promotes the activation of the RAS-ERK1/2 cascade. In its basal state, SHP2 exists in an autoinhibited closed conformation because of an intramolecular interaction between its N-SH2 and protein tyrosine phosphatase (PTP) domains. Binding to pTyr ligands present on growth factor receptors and adaptor proteins with its N-SH2 domain localizes SHP2 to its substrates and frees the active site from allosteric inhibition. Germline mutations in SHP2 are known to cause both Noonan syndrome (NS) and LEOPARD syndrome (LS), two clinically similar autosomal dominant developmental disorders. NS-associated SHP2 mutants display elevated phosphatase activity, while LS-associated SHP2 mutants exhibit reduced catalytic activity. A conundrum in how clinically similar diseases result from mutations to SHP2 that have opposite effects on this enzyme’s catalytic functionality exists. Here we report a comprehensive investigation of the kinetic, structural, dynamic, and biochemical signaling properties of the wild type as well as all reported LS-associated SHP2 mutants. The results reveal that LS-causing mutations not only affect SHP2 phosphatase activity but also induce a weakening of the intramolecular interaction between the N-SH2 and PTP domains, leading to mutants that are more readily activated by competing pTyr ligands. Our data also indicate that the residual phosphatase activity associated with the LS SHP2 mutant is required for enhanced ERK1/2 activation. Consequently, catalytically impaired SHP2 mutants could display gain-of-function properties because of their ability to localize to the vicinity of substrates for longer periods of time, thereby affording the opportunity for prolonged substrate turnover and sustained RAS-ERK1/2 activation. PMID:24935154

Charge Transfer and Catalysis at the Metal Support Interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, Lawrence Robert

Kinetic, electronic, and spectroscopic characterization of model Pt–support systems are used to demonstrate the relationship between charge transfer and catalytic activity and selectivity. The results show that charge flow controls the activity and selectivity of supported metal catalysts. This dissertation builds on extensive existing knowledge of metal–support interactions in heterogeneous catalysis. The results show the prominent role of charge transfer at catalytic interfaces to determine catalytic activity and selectivity. Further, this research demonstrates the possibility of selectively driving catalytic chemistry by controlling charge flow and presents solid-state devices and doped supports as novel methods for obtaining electronic control over catalyticmore » reaction kinetics.« less

Structural analysis of nickel doped cerium oxide catalysts for fuel reforming in solid oxide fuel cells

NASA Astrophysics Data System (ADS)

Cavendish, Rio

As world energy demands increase, research into more efficient energy production methods has become imperative. Heterogeneous catalysis and nanoscience are used to promote chemical transformations important for energy production. These concepts are important in solid oxide fuel cells (SOFCs) which have attracted attention because of their potential to provide an efficient and environmentally favorable power generation system. The SOFC is also fuel-flexible with the ability to run directly on many fuels other than hydrogen. Internal fuel reforming directly in the anode of the SOFC would greatly reduce the cost and complexity of the device. Methane is the simplest hydrocarbon and a main component in natural gas, making it useful when testing catalysts on the laboratory scale. Nickel (Ni) and gadolinium (Gd) doped ceria (CeO 2) catalysts for potential use in the SOFC anode were synthesized with a spray drying method and tested for catalytic performance using partial oxidation of methane and steam reforming. The relationships between catalytic performance and structure were then investigated using X-ray diffraction, transmission electron microscopy, and environmental transmission electron microscopy. The possibility of solid solutions, segregated phases, and surface layers of Ni were explored. Results for a 10 at.% Ni in CeO2 catalyst reveal a poor catalytic behavior while a 20 at.% Ni in CeO2 catalyst is shown to have superior activity. The inclusion of both 10 at.% Gd and 10 at.% Ni in CeO2 enhances the catalytic performance. Analysis of the presence of Ni in all 3 samples reveals Ni heterogeneity and little evidence for extensive solid solution doping. Ni is found in small domains throughout CeO2 particles. In the 20 at.% Ni sample a segregated, catalytically active NiO phase is observed. Overall, it is found that significant interaction between Ni and CeO2 occurs that could affect the synthesis and functionality of the SOFC anode.

Polypeptides having xylanase activity and polynucleotides encoding same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spodsberg, Nikolaj; Shaghasi, Tarana

The present invention relates to polypeptides having xylanase activity, catalytic domains, and carbohydrate binding domains, and polynucleotides encoding the polypeptides, catalytic domains, and carbohydrate binding domains. The present invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains, and carbohydrate binding domains.

Polypeptides having endoglucanase activity and polynucleotides encoding same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Spodsberg, Nikolaj; Shagasi, Tarana

The present invention relates to isolated polypeptides having endoglucanase activity, catalytic domains, cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains or cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains or cellulose binding domains.

Polypeptides having endoglucanase activity and polynucleotides encoding same

DOEpatents

Spodsberg, Nikolaj; Shagasi, Tarana

2015-06-30

The present invention relates to isolated polypeptides having endoglucanase activity, catalytic domains, cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains or cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains or cellulose binding domains.

Polypeptides having cellobiohydrolase activity and polynucleotides encoding same

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stringer, Mary Ann; McBrayer, Brett

2016-11-29

The present invention relates to isolated polypeptides having cellobiohydrolase activity, catalytic domains, and cellulose binding domains and polynucleotides encoding the polypeptides, catalytic domains, and cellulose binding domains. The invention also relates to nucleic acid constructs, vectors, and host cells comprising the polynucleotides as well as methods of producing and using the polypeptides, catalytic domains, or cellulose binding domains.

Enhancing Human Spermine Synthase Activity by Engineered Mutations

PubMed Central

Zhang, Zhe; Zheng, Yueli; Petukh, Margo; Pegg, Anthony; Ikeguchi, Yoshihiko; Alexov, Emil

2013-01-01

Spermine synthase (SMS) is an enzyme which function is to convert spermidine into spermine. It was shown that gene defects resulting in amino acid changes of the wild type SMS cause Snyder-Robinson syndrome, which is a mild-to-moderate mental disability associated with osteoporosis, facial asymmetry, thin habitus, hypotonia, and a nonspecific movement disorder. These disease-causing missense mutations were demonstrated, both in silico and in vitro, to affect the wild type function of SMS by either destabilizing the SMS dimer/monomer or directly affecting the hydrogen bond network of the active site of SMS. In contrast to these studies, here we report an artificial engineering of a more efficient SMS variant by transferring sequence information from another organism. It is confirmed experimentally that the variant, bearing four amino acid substitutions, is catalytically more active than the wild type. The increased functionality is attributed to enhanced monomer stability, lowering the pKa of proton donor catalytic residue, optimized spatial distribution of the electrostatic potential around the SMS with respect to substrates, and increase of the frequency of mechanical vibration of the clefts presumed to be the gates toward the active sites. The study demonstrates that wild type SMS is not particularly evolutionarily optimized with respect to the reaction spermidine → spermine. Having in mind that currently there are no variations (non-synonymous single nucleotide polymorphism, nsSNP) detected in healthy individuals, it can be speculated that the human SMS function is precisely tuned toward its wild type and any deviation is unwanted and disease-causing. PMID:23468611

Catalytic dehydrogenation of alcohol over solid-state molybdenum sulfide clusters with an octahedral metal framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamiguchi, Satoshi, E-mail: kamigu@riken.jp; Organometallic Chemistry Laboratory, RIKEN, 2-1 Hirosawa, Wako City, Saitama 351-0198; Okumura, Kazu

Graphical abstract: - Highlights: • Solid-state molybdenum sulfide clusters catalyzed the dehydrogenation of alcohol. • The dehydrogenation proceeded without the addition of any oxidants. • The catalytic activity developed when the cluster was activated at 300–500 °C in H{sub 2}. • The Lewis-acidic molybdenum atom and basic sulfur ligand were catalytically active. • The clusters function as bifunctional acid–base catalysts. - Abstract: Solid-state molybdenum sulfide clusters with an octahedral metal framework, the superconducting Chevrel phases, are applied to catalysis. A copper salt of a nonstoichiometric sulfur-deficient cluster, Cu{sub x}Mo{sub 6}S{sub 8–δ} (x = 2.94 and δ ≈ 0.3), is storedmore » in air for more than 90 days. When the oxygenated cluster is thermally activated in a hydrogen stream above 300 °C, catalytic activity for the dehydrogenation of primary alcohols to aldehydes and secondary alcohols to ketones develops. The addition of pyridine or benzoic acid decreases the dehydrogenation activity, indicating that both a Lewis-acidic coordinatively unsaturated molybdenum atom and a basic sulfur ligand synergistically act as the catalytic active sites.« less

Immobilization of chloroperoxidase on mesoporous materials for the oxidation of 4,6-dimethyldibenzothiophene, a recalcitrant organic sulfur compound present in petroleum fractions.

PubMed

Terrés, Eduardo; Montiel, Mayra; Le Borgne, Sylvie; Torres, Eduardo

2008-01-01

The catalytic potential of chloroperoxidase (CPO) immobilized on mesoporous materials was evaluated for the oxidation of 4,6-dimethyldibenzothiophene in water/acetonitrile mixtures. Two different types of materials were used for the immobilization: a metal containing Al-MCM-41 material with a pore size of 26 A and SBA-16 materials with three different pore sizes: 40, 90 and 117 A. The SBA-16 40 A did not retain any CPO. The nature and the pore size of the material affected the catalytic activity of the enzyme as well as its stability. Compared to the free enzyme, the thermal stability of CPO at 45 degrees C was two and three times higher than when immobilized on Al-MCM-41 and SBA-16 90 A, respectively.

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2013 CFR

2013-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device... regenerator under paragraph (b) of this section which commences construction, reconstruction, or modification...

40 CFR 60.100 - Applicability, designation of affected facility, and reconstruction.

Code of Federal Regulations, 2014 CFR

2014-07-01

... petroleum refineries: fluid catalytic cracking unit catalyst regenerators, fuel gas combustion devices, and... petroleum refinery. (b) Any fluid catalytic cracking unit catalyst regenerator or fuel gas combustion device... regenerator under paragraph (b) of this section which commences construction, reconstruction, or modification...

Improvement of activity and stability of chloroperoxidase by chemical modification

PubMed Central

Liu, Jian-Zhong; Wang, Min

2007-01-01

Background Enzymes show relative instability in solvents or at elevated temperature and lower activity in organic solvent than in water. These limit the industrial applications of enzymes. Results In order to improve the activity and stability of chloroperoxidase, chloroperoxidase was modified by citraconic anhydride, maleic anhydride or phthalic anhydride. The catalytic activities, thermostabilities and organic solvent tolerances of native and modified enzymes were compared. In aqueous buffer, modified chloroperoxidases showed similar Km values and greater catalytic efficiencies kcat/Km for both sulfoxidation and oxidation of phenol compared to native chloroperoxidase. Of these modified chloroperoxidases, citraconic anhydride-modified chloroperoxidase showed the greatest catalytic efficiency in aqueous buffer. These modifications of chloroperoxidase increased their catalytic efficiencies for sulfoxidation by 12%~26% and catalytic efficiencies for phenol oxidation by 7%~53% in aqueous buffer. However, in organic solvent (DMF), modified chloroperoxidases had lower Km values and higher catalytic efficiencies kcat/Km than native chloroperoxidase. These modifications also improved their thermostabilities by 1~2-fold and solvent tolerances of DMF. CD studies show that these modifications did not change the secondary structure of chloroperoxidase. Fluorescence spectra proved that these modifications changed the environment of tryptophan. Conclusion Chemical modification of epsilon-amino groups of lysine residues of chloroperoxidase using citraconic anhydride, maleic anhydride or phthalic anhydride is a simple and powerful method to enhance catalytic properties of enzyme. The improvements of the activity and stability of chloroperoxidase are related to side chain reorientations of aromatics upon both modifications. PMID:17511866

Dimerization Interface of 3-Hydroxyacyl-CoA Dehydrogenase Tunes the Formation of Its Catalytic Intermediate

PubMed Central

Jin, Ying-Hua; Fan, Jun; Sun, Fei

2014-01-01

3-hydroxyacyl-CoA dehydrogenase (HAD, EC 1.1.1.35) is a homodimeric enzyme localized in the mitochondrial matrix, which catalyzes the third step in fatty acid β-oxidation. The crystal structures of human HAD and subsequent complexes with cofactor/substrate enabled better understanding of HAD catalytic mechanism. However, numerous human diseases were found related to mutations at HAD dimerization interface that is away from the catalytic pocket. The role of HAD dimerization in its catalytic activity needs to be elucidated. Here, we solved the crystal structure of Caenorhabditis elegans HAD (cHAD) that is highly conserved to human HAD. Even though the cHAD mutants (R204A, Y209A and R204A/Y209A) with attenuated interactions on the dimerization interface still maintain a dimerization form, their enzymatic activities significantly decrease compared to that of the wild type. Such reduced activities are in consistency with the reduced ratios of the catalytic intermediate formation. Further molecular dynamics simulations results reveal that the alteration of the dimerization interface will increase the fluctuation of a distal region (a.a. 60–80) that plays an important role in the substrate binding. The increased fluctuation decreases the stability of the catalytic intermediate formation, and therefore the enzymatic activity is attenuated. Our study reveals the molecular mechanism about the essential role of the HAD dimerization interface in its catalytic activity via allosteric effects. PMID:24763278

Catalytic ozonation of pentachlorophenol in aqueous solutions using granular activated carbon

NASA Astrophysics Data System (ADS)

Asgari, Ghorban; Samiee, Fateme; Ahmadian, Mohammad; Poormohammadi, Ali; solimanzadeh, Bahman

2017-03-01

The efficiency of granular activated carbon (GAC) was investigated in this study as a catalyst for the elimination of pentachlorophenol (PCP) from contaminated streams in a laboratory-scale semi-batch reactor. The influence of important parameters including solution pH (2-10), radical scavenger (tert-butanol, 0.04 mol/L), catalyst dosage (0.416-8.33 g/L), initial PCP concentration (100-1000 mg/L) and ozone flow rate (2.3-12 mg/min) was examined on the efficiency of the catalytic ozonation process (COP) in degradation and mineralization of PCP in aqueous solution. The experimental results showed that catalytic ozonation with GAC was most effective at pH of 8 with ozone flow rate of 12 mg/min and a GAC dosage of 2 g. Compared to the sole ozonation process (SOP), the removal levels of PCP and COP were, 98, and 79 %, respectively. The degradation rate of kinetics was also investigated. The results showed that using a GAC catalyst in the ozonation of PCP produced an 8.33-fold increase in rate kinetic compared to the SOP under optimum conditions. Tert-butanol alcohol (TBA) was used as a radical scavenger. The results demonstrated that COP was affected less by TBA than by SOP. These findings suggested that GAC acts as a suitable catalyst in COP to remove refractory pollutants from aqueous solution.

A PTPN11 allele encoding a catalytically impaired SHP2 protein in a patient with a Noonan syndrome phenotype.

PubMed

Edwards, Jonathan J; Martinelli, Simone; Pannone, Luca; Lo, Ivan Fai-Man; Shi, Lisong; Edelmann, Lisa; Tartaglia, Marco; Luk, Ho-Ming; Gelb, Bruce D

2014-09-01

The RASopathies are a relatively common group of phenotypically similar and genetically related autosomal dominant genetic syndromes caused by missense mutations affecting genes participating in the RAS/mitogen-activated protein kinase (MAPK) pathway that include Noonan syndrome (NS) and Noonan syndrome with multiple lentigines (NSML, formerly LEOPARD syndrome). NS and NSML can be difficult to differentiate during infancy, but the presence of multiple lentigines, café au lait spots, and specific cardiac defects facilitate the diagnosis. Furthermore, individual PTPN11 missense mutations are highly specific to each syndrome and engender opposite biochemical alterations on the function of SHP-2, the protein product of that gene. Here, we report on a 5-year-old male with two de novo PTPN11 mutations in cis, c.1471C>T (p.Pro491Ser), and c.1492C>T (p.Arg498Trp), which are associated with NS and NSML, respectively. This boy's phenotype is intermediate between NS and NSML with facial dysmorphism, short stature, mild global developmental delay, pulmonic stenosis, and deafness but absence of café au lait spots or lentigines. The double-mutant SHP-2 was found to be catalytically impaired. This raises the question of whether clinical differences between NS and NSML can be ascribed solely to the relative SHP-2 catalytic activity. © 2014 Wiley Periodicals, Inc.

Ni0 encapsulated in N-doped carbon nanotubes for catalytic reduction of highly toxic hexavalent chromium

NASA Astrophysics Data System (ADS)

Yao, Yunjin; Zhang, Jie; Chen, Hao; Yu, Maojing; Gao, Mengxue; Hu, Yi; Wang, Shaobin

2018-05-01

N-doped carbon nanotubes encapsulating Ni0 nanoparticles (Ni@N-C) were fabricated via thermal reduction of dicyandiamide and NiCl2·6H2O, and used to remove CrVI in polluted water. The resultant products present an excellent catalytic activity for CrVI reduction using formic acid under relatively mild conditions. The CrVI reduction efficiency of Ni@N-C was significantly affected by the preparation conditions including the mass of nickel salt and synthesis temperatures. The impacts of several reaction parameters, such as initial concentrations of CrVI and formic acid, solution pH and temperatures, as well as inorganic anions in solution on CrVI reduction efficiency were also evaluated in view of scalable industrial applications. Owing to the synergistic effects amongst tubes-coated Ni0, doped nitrogen, oxygen containing groups, and the configuration of carbon nanotubes, Ni@N-C catalysts exhibit excellent catalytic activity and recyclable capability for CrVI reduction. Carbon shell can efficiently protect inner Ni0 core and N species from corrosion and subsequent leaching, while Ni0 endows the Ni@N-C catalysts with ferromagnetism, so that the composites can be easily separated via a permanent magnet. This study opens up an avenue for design of N-doped carbon nanotubes encapsulating Ni0 nanoparticles with high CrVI removal efficiency and magnetic recyclability as low-cost catalysts for industrial applications.

Determining the Catalytic Activity of Transition Metal-Doped TiO2 Nanoparticles Using Surface Spectroscopic Analysis

NASA Astrophysics Data System (ADS)

Yang, Sena; Lee, Hangil

2017-11-01

The modified TiO2 nanoparticles (NPs) to enhance their catalytic activities by doping them with the five transition metals (Cr, Mn, Fe, Co, and Ni) have been investigated using various surface analysis techniques such as scanning electron microscopy (SEM), Raman spectroscopy, scanning transmission X-ray microscopy (STXM), and high-resolution photoemission spectroscopy (HRPES). To compare catalytic activities of these transition metal-doped TiO2 nanoparticles (TM-TiO2) with those of TiO2 NPs, we monitored their performances in the catalytic oxidation of 2-aminothiophenol (2-ATP) by using HRPES and on the oxidation of 2-ATP in aqueous solution by taking electrochemistry (EC) measurements. As a result, we clearly investigate that the increased defect structures induced by the doped transition metal are closely correlated with the enhancement of catalytic activities of TiO2 NPs and confirm that Fe- and Co-doped TiO2 NPs can act as efficient catalysts.

Heterogeneous catalytic ozonation of biologically pretreated Lurgi coal gasification wastewater using sewage sludge based activated carbon supported manganese and ferric oxides as catalysts.

PubMed

Zhuang, Haifeng; Han, Hongjun; Hou, Baolin; Jia, Shengyong; Zhao, Qian

2014-08-01

Sewage sludge of biological wastewater treatment plant was converted into sewage sludge based activated carbon (SBAC) with ZnCl₂ as activation agent, which supported manganese and ferric oxides as catalysts (including SBAC) to improve the performance of ozonation of real biologically pretreated Lurgi coal gasification wastewater. The results indicated catalytic ozonation with the prepared catalysts significantly enhanced performance of pollutants removal and the treated wastewater was more biodegradable and less toxic than that in ozonation alone. On the basis of positive effect of higher pH and significant inhibition of radical scavengers in catalytic ozonation, it was deduced that the enhancement of catalytic activity was responsible for generating hydroxyl radicals and the possible reaction pathway was proposed. Moreover, the prepared catalysts showed superior stability and most of toxic and refractory compounds were eliminated at successive catalytic ozonation runs. Thus, the process with economical, efficient and sustainable advantages was beneficial to engineering application. Copyright © 2014 Elsevier Ltd. All rights reserved.

Deprotonation states of the two active site water molecules regulate the binding of protein phosphatase 5 with its substrate: A molecular dynamics study.

PubMed

Wang, Lingyun; Yan, Feng

2017-10-01

Protein phosphatase 5 (PP5), mainly localized in human brain, can dephosphorylate tau protein whose high level of phosphorylation is related to Alzheimer's disease. Similar to other protein phosphatases, PP5 has a conserved motif in the catalytic domain that contains two binding sites for manganese (Mn 2+ ) ions. Structural data indicate that two active site water molecules, one bridging the two Mn 2+ ions and the other terminally coordinated with one of the Mn 2+ ions (Mn1), are involved in catalysis. Recently, a density functional theory study revealed that the two water molecules can be both deprotonated to keep a neutral active site for catalysis. The theoretical study gives us an insight into the catalytic mechanism of PP5, but the knowledge of how the deprotonation states of the two water molecules affect the binding of PP5 with its substrate is still lacking. To approach this problem, molecular dynamics simulations were performed to model the four possible deprotonation states. Through structural, dynamical and energetic analyses, the results demonstrate that the deprotonation states of the two water molecules affect the structure of the active site including the distance between the two Mn 2+ ions and their coordination, impact the interaction energy of residues R275, R400 and H304 which directly interact with the substrate phosphoserine, and mediate the dynamics of helix αJ which is involved in regulation of the enzyme's activity. Furthermore, the deprotonation state that is preferable for PP5 binding of its substrate has been identified. These findings could provide new design strategy for PP5 inhibitor. © 2017 The Protein Society.

Retro-binding thrombin active site inhibitors: identification of an orally active inhibitor of thrombin catalytic activity.

PubMed

Iwanowicz, Edwin J; Kimball, S David; Lin, James; Lau, Wan; Han, W-C; Wang, Tammy C; Roberts, Daniel G M; Schumacher, W A; Ogletree, Martin L; Seiler, Steven M

2002-11-04

A series of retro-binding inhibitors of human alpha-thrombin was prepared to elucidate structure-activity relationships (SAR) and optimize in vivo performance. Compounds 9 and 11, orally active inhibitors of thrombin catalytic activity, were identified to be efficacious in a thrombin-induced lethality model in mice.

A three-nucleotide helix I is sufficient for full activity of a hammerhead ribozyme: advantages of an asymmetric design.

PubMed Central

Tabler, M; Homann, M; Tzortzakaki, S; Sczakiel, G

1994-01-01

Trans-cleaving hammerhead ribozymes with long target-specific antisense sequences flanking the catalytic domain share some features with conventional antisense RNA and are therefore termed 'catalytic antisense RNAs'. Sequences 5' to the catalytic domain form helix I and sequences 3' to it form helix III when complexed with the target RNA. A catalytic antisense RNA of more than 400 nucleotides, and specific for the human immunodeficiency virus type 1 (HIV-1), was systematically truncated within the arm that constituted originally a helix I of 128 base pairs. The resulting ribozymes formed helices I of 13, 8, 5, 3, 2, 1 and 0 nucleotides, respectively, and a helix III of about 280 nucleotides. When their in vitro cleavage activity was compared with the original catalytic antisense RNA, it was found that a helix I of as little as three nucleotides was sufficient for full endonucleolytic activity. The catalytically active constructs inhibited HIV-1 replication about four-fold more effectively than the inactive ones when tested in human cells. A conventional hammerhead ribozyme having helices of just 8 nucleotides on either side failed to cleave the target RNA in vitro when tested under the conditions for catalytic antisense RNA. Cleavage activity could only be detected after heat-treatment of the ribozyme substrate mixture which indicates that hammerhead ribozymes with short arms do not associate as efficiently to the target RNA as catalytic antisense RNA. The requirement of just a three-nucleotide helix I allows simple PCR-based generation strategies for asymmetric hammerhead ribozymes. Advantages of an asymmetric design will be discussed. Images PMID:7937118

Structural and Dynamic Insights into the Mechanism of Allosteric Signal Transmission in ERK2-Mediated MKP3 Activation.

PubMed

Lu, Chang; Liu, Xin; Zhang, Chen-Song; Gong, Haipeng; Wu, Jia-Wei; Wang, Zhi-Xin

2017-11-21

The mitogen-activated protein kinases (MAPKs) are key components of cellular signal transduction pathways, which are down-regulated by the MAPK phosphatases (MKPs). Catalytic activity of the MKPs is controlled both by their ability to recognize selective MAPKs and by allosteric activation upon binding to MAPK substrates. Here, we use a combination of experimental and computational techniques to elucidate the molecular mechanism for the ERK2-induced MKP3 activation. Mutational and kinetic study shows that the 334 FNFM 337 motif in the MKP3 catalytic domain is essential for MKP3-mediated ERK2 inactivation and is responsible for ERK2-mediated MKP3 activation. The long-term molecular dynamics (MD) simulations further reveal a complete dynamic process in which the catalytic domain of MKP3 gradually changes to a conformation that resembles an active MKP catalytic domain over the time scale of the simulation, providing a direct time-dependent observation of allosteric signal transmission in ERK2-induced MKP3 activation.

Understanding Anionic "Ligandless" Palladium Species in the Mizoroki-Heck Reaction.

PubMed

Schroeter, Felix; Strassner, Thomas

2018-05-07

The anionic complex [NBu 4 ][Pd(DMSO)Cl 3 ], as a "ligandless" system, was shown to be an active catalyst in the Mizoroki-Heck coupling of aryl chlorides in the absence of strongly σ-donating ligands. To investigate the experimentally observed influence of halides and the amount of water on the catalytic activity, we employed a combination of experiments and theoretical calculations. The presence of water was shown to be critical for the formation of the active palladium(0) species by oxidation of in situ generated tributylamine. Oxidative addition to an anionic palladium(0) species was found to be the rate-determining step of the catalytic cycle. For the ensuing steps, both neutral and anionic pathways were considered. It was shown that, in the absence of strongly σ-donating neutral ligands, chloride ions stabilize the catalytic intermediates. Therefore, an anionic pathway is preferred, which explains the need for tetrabutylammonium chloride as an additive. The study of the influence of bromide ions on the catalytic activity revealed that the strongly exergonic displacement of the neutral substrates by bromide ions lowers the catalytic activity.

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

Reversible amorphization and the catalytically active state of crystalline Co3O4 during oxygen evolution.

PubMed

Bergmann, Arno; Martinez-Moreno, Elias; Teschner, Detre; Chernev, Petko; Gliech, Manuel; de Araújo, Jorge Ferreira; Reier, Tobias; Dau, Holger; Strasser, Peter

2015-10-12

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 Co(3+/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.

Catalytic Oxidation of Chlorobenzene over MnxCe1-xO2/HZSM-5 Catalysts: A Study with Practical Implications.

PubMed

Weng, Xiaole; Sun, Pengfei; Long, Yu; Meng, Qingjie; Wu, Zhongbiao

2017-07-18

Industrial-use catalysts usually encounter severe deactivation after long-term operation for catalytic oxidation of chlorinate volatile organic compounds (CVOCs), which becomes a "bottleneck" for large-scale application of catalytic combustion technology. In this work, typical acidic solid-supported catalysts of Mn x Ce 1-x O 2 /HZSM-5 were investigated for the catalytic oxidation of chlorobenzene (CB). The activation energy (E a ), Brønsted and Lewis acidities, CB adsorption and activation behaviors, long-term stabilities, and surficial accumulation compounds (after aging) were studied using a range of analytical techniques, including XPS, H 2 -TPR, pyridine-IR, DRIFT, and O 2 -TP-Ms. Experimental results revealed that the Brønsted/Lewis (B/L) ratio of Mn x Ce 1-x O 2 /HZSM-5 catalysts could be adjusted by ion exchange of H• (in HZSM-5) with Mn n+ (where the exchange with Ce 4+ did not distinctly affect the acidity); the long-term aged catalysts could accumulate ca. 14 organic compounds at surface, including highly toxic tetrachloromethane, trichloroethylene, tetrachloroethylene, o-dichlorobenzene, etc.; high humid operational environment could ensure a stable performance for Mn x Ce 1-x O 2 /HZSM-5 catalysts; this was due to the effective removal of Cl• and coke accumulations by H 2 O washing, and the distinct increase of Lewis acidity by the interaction of H 2 O with HZSM-5. This work gives an in-depth view into the CB oxidation over acidic solid-supported catalysts and could provide practical guidelines for the rational design of reliable catalysts for industrial applications.

Catalytic Properties of Botulinum Neurotoxins Subtypes A3 and A4

PubMed Central

Henkel, James S.; Jacobson, Mark; Tepp, William; Pier, Christina; Johnson, Eric A.; Barbieri, Joseph T.

2009-01-01

Botulinum toxins (BoNT) are zinc proteases (serotypes A-G) which cause flaccid paralysis through the cleavage of SNARE proteins within motor neurons. BoNT/A was originally organized into two subtypes: BoNT/A1 and BoNT/A2, which are ~ 95 % homologous and possess similar catalytic activities. Subsequently, two additional subtypes were identified; BoNT/A3 (Loch Maree), and BoNT/A4 (657Ba), which have 81 and 88% homology with BoNT/A1, respectively. Alignment studies predicted that BoNT/A3 and BoNT/A4 were sufficiently different to BoNT/A1 to affect SNAP25 binding and cleavage. Recombinant Light Chain (LC) of BoNT/A3 (LC/A3) and BoNT/A4 (LC/A4) were subjected to biochemical analysis. LC/A3 cleaved SNAP25 at 50% the rate of LC/A1, but cleaved SNAPtide® at a faster rate than LC/A1, while LC/A4 cleaved SNAP25 and SNAPtide® at slower rates than LC/A1. LC/A3 and LC/A4 had similar Kms for SNAP25 relative to LC/A1, while the kcat for LC/A4 was 10- fold slower than LC/A1, suggesting a defect in substrate cleavage. Neither LC/A3 nor LC/A4 possessed autocatalytic activity, a property of LC/A1 and LC/A2. Thus, the four subtypes of BoNT/A bind SNAP25 with similar affinity but have different catalytic capacities for SNAP25 cleavage, SNAPtide® cleavage, and autocatalysis. The catalytic properties identified among the subtypes of LC/A may influence strategies for the development of small molecule- or peptide- inhibitors as therapies against botulism. PMID:19256469

DOE Office of Scientific and Technical Information (OSTI.GOV)

Morra, Simone; Maurelli, Sara; Chiesa, Mario

A conserved cysteine located in the signature motif of the catalytic center (H-cluster) of [FeFe]-hydrogenases functions in proton transfer. This residue corresponds to C298 in Clostridium acetobutylicum CaHydA. Despite the chemical and structural difference, the mutant C298D retains fast catalytic activity, while replacement with any other amino acid caused significant activity loss. Given the proximity of C298 to the H-cluster, the effect of the C298D mutation on the catalytic center was studied by continuous wave (CW) and pulse electron paramagnetic resonance (EPR) and by Fourier transform infrared (FTIR) spectroscopies. Comparison of the C298D mutant with the wild type CaHydA bymore » CW and pulse EPR showed that the electronic structure of the center is not altered. FTIR spectroscopy confirmed that absorption peak values observed in the mutant are virtually identical to those observed in the wild type, indicating that the H-cluster is not generally affected by the mutation. Significant differences were observed only in the inhibited state Hox-CO: the vibrational modes assigned to the COexo and Fed-CO in this state are shifted to lower values in C298D, suggesting different interaction of these ligands with the protein moiety when C298 is changed to D298. More relevant to the catalytic cycle, the redox equilibrium between the Hox and Hred states is modified by the mutation, causing a prevalence of the oxidized state. This work highlights how the interactions between the protein environment and the H-cluster, a dynamic closely interconnected system, can be engineered and studied in the perspective of designing bio-inspired catalysts and mimics.« less

[New iron-porphyrin/vanadium-substituted polyoxometalate catalyst: synthesis, characterization and catalytic activity].

PubMed

Dong, Xiao-li; Zhang, Zhen-cheng; An, Qing-da; Zhang, Shao-yin; Wang, Shao-jun

2007-12-01

A new kind of iron-porphyrin/vanadium-substituted polyoxometalate coordination compound was synthesized by the ion exchange reaction of FeTTMAPPI and H5PMo10V2o40 in solution. The new catalyst was characterized by IR spectrometry and UV-Vis spectrometry. As an excellent catalyst, its effects on benzene hydroxylation and catalytic capabilities were studied with H2O2 solution as the oxidant. The results indicated that the products contained the conjugated structure of porphyrin and the cage structure of polyoxometalate, the V atom in polyoxometalate is the main centre of catalytic activity, meanwhile the presence of iron-porphyrin could increase its catalytic activity greatly.

A catalytic chiral gel microfluidic reactor assembled via dynamic covalent chemistry† †Electronic supplementary information (ESI) available: Experimental details, additional characterization and catalytic data. See DOI: 10.1039/c5sc00314h Click here for additional data file.

PubMed Central

Liu, Haoliang; Feng, Juan; Chen, Liuping

2015-01-01

A novel dynamic covalent gel strategy is reported to immobilize an asymmetric catalyst within the channels of a microfluidic flow reactor. A layer of a catalytically active Mn–salen dynamic covalent imine gel matrix was coated onto a functionalized capillary. Mn–salen active moiety was incorporated into dynamic covalent imine gel matrix via the reaction of a chiral Mn–salen dialdehyde unit with a tetraamine linker. The catalytic activity of the capillary reactor has been demonstrated in enantioselective kinetic resolution of secondary alcohols. PMID:28706652

A remote palm domain residue of RB69 DNA polymerase is critical for enzyme activity and influences the conformation of the active site.

PubMed

Jacewicz, Agata; Trzemecka, Anna; Guja, Kip E; Plochocka, Danuta; Yakubovskaya, Elena; Bebenek, Anna; Garcia-Diaz, Miguel

2013-01-01

Non-conserved amino acids that are far removed from the active site can sometimes have an unexpected effect on enzyme catalysis. We have investigated the effects of alanine replacement of residues distant from the active site of the replicative RB69 DNA polymerase, and identified a substitution in a weakly conserved palm residue (D714A), that renders the enzyme incapable of sustaining phage replication in vivo. D714, located several angstroms away from the active site, does not contact the DNA or the incoming dNTP, and our apoenzyme and ternary crystal structures of the Pol(D714A) mutant demonstrate that D714A does not affect the overall structure of the protein. The structures reveal a conformational change of several amino acid side chains, which cascade out from the site of the substitution towards the catalytic center, substantially perturbing the geometry of the active site. Consistent with these structural observations, the mutant has a significantly reduced k pol for correct incorporation. We propose that the observed structural changes underlie the severe polymerization defect and thus D714 is a remote, non-catalytic residue that is nevertheless critical for maintaining an optimal active site conformation. This represents a striking example of an action-at-a-distance interaction.

Kinetic study of hydroxytyrosol oxidation and its related compounds by Red Globe grape polyphenol oxidase.

PubMed

García-García, María Inmaculada; Hernández-García, Samanta; Sánchez-Ferrer, Álvaro; García-Carmona, Francisco

2013-06-26

Red Globe grape polyphenol oxidase, partially purified using phase partitioning with Triton-X114, was used to study the oxidation of hydroxytytosol (HT) and its related compounds tyrosol (TS), tyrosol acetate (TSA), and hydroxytyrosol acetate (HTA). The enzyme showed activity toward both monophenols (monophenolase activity) and o-diphenols (diphenolase activity) with a pH optimum (pH 6.5) that was independent of the phenol used. However, the optimal temperature for diphenolase activity was substrate-dependent, with a broad optimum of 25-65 °C for HT, compared with the maximum obtained for HTA (40 °C). Monophenolase activity showed the typical lag period, which was modulated by pH, substrate and enzyme concentrations, and the presence of catalytic amounts of o-diphenols. When the catalytic power (Vmax/K(M)) was determined for both activities, higher values were observed for o-diphenols than for monophenols: 9-fold higher for the HT/TS pair and 4-fold higher for HTA/TSA pair. Surprisingly, this ratio was equally higher for TSA (2.2-fold) compared with that of TS, whereas no such effect was observed for o-diphenols. This higher efficiency of TSA could be related to its greater hydrophobicity. Acetyl modification of these phenols not only changes the kinetic parameters of the enzyme but also affects their antioxidant activity (ORAC-FL assays), which is lower in HTA than in HT.

Catalytic wet peroxide oxidation of benzoic acid over Fe/AC catalysts: Effect of nitrogen and sulfur co-doped activated carbon.

PubMed

Qin, Hangdao; Xiao, Rong; Chen, Jing

2018-06-01

The parent activated carbon (ACP) was modified with urea and thiourea to obtain N-doped activated carbon (ACN) and N, S co-doped activated carbon (ACNS), respectively. Iron supported on activated carbon (Fe/ACP, Fe/ACN and Fe/ACNS) were prepared and worked as catalyst for catalytic wet peroxide oxidation of benzoic acid (BA). The catalysts were characterized by N 2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM), and their performance was evaluated in terms of benzoic acid and TOC removal. The results indicated the doped N and S improved the adsorption capacity as well as catalytic activity of activated carbon. Besides, the catalytic activity toward benzoic acid degradation was found to be enhanced by Fe/ACNS compared to that of Fe/ACP and Fe/ACN. The enhanced catalytic performance was attributed to the presence of the nitrogen and sulfur atoms may serve to improve the relative amount of Fe 2+ on iron oxide surface and also help prevent leaching of Fe. It was also observed that the stability or reutilization of Fe/ACNS catalyst was fairly good. Copyright © 2018 Elsevier B.V. All rights reserved.

Metal-organic frameworks: versatile heterogeneous catalysts for efficient catalytic organic transformations.

PubMed

Chughtai, Adeel H; Ahmad, Nazir; Younus, Hussein A; Laypkov, A; Verpoort, Francis

2015-10-07

Novel catalytic materials are highly demanded to perform a variety of catalytic organic reactions. MOFs combine the benefits of heterogeneous catalysis like easy post reaction separation, catalyst reusability, high stability and homogeneous catalysis such as high efficiency, selectivity, controllability and mild reaction conditions. The possible organization of active centers like metallic nodes, organic linkers, and their chemical synthetic functionalization on the nanoscale shows potential to build up MOFs particularly modified for catalytic challenges. In this review, we have summarized the recent research progress in heterogeneous catalysis by MOFs and their catalytic behavior in various organic reactions, highlighting the key features of MOFs as catalysts based on the active sites in the framework. Examples of their post functionalization, inclusion of active guest species and metal nanoparticles have been discussed. Finally, the use of MOFs as catalysts for asymmetric heterogeneous catalysis and stability of MOFs has been presented as separate sections.

A recyclable Au(I) catalyst for selective homocoupling of arylboronic acids: significant enhancement of nano-surface binding for stability and catalytic activity.

PubMed

Zhang, Xin; Zhao, Haitao; Wang, Jianhui

2010-08-01

Au nanoparticles stabilized by polystyrene-co-polymethacrylic acid microspheres (PS-co-PMAA) were prepared and characterized via X-ray diffraction (XRD), and transmission electron microscope (TEM). The Au nanoparticles supported on the microspheres showed highly selective catalytic activity for homo-coupling reactions of arylboronic acids in a system of aryl-halides and arylboronic acids. X-ray photoelectron spectroscopy (XPS) spectra of the catalyst shows large amounts of Au(I) complexes band to the surface of the Au nanoparticles, which contributes to the selective homocoupling of the arylboronic acids. More importantly, this supported Au complex is a highly recyclable catalyst. The supported Au catalyst can be recycled and reused at least 6 times for a phenylboronic acid reactant, whereas the parent complex shows very low catalytic activity for this compound. The high catalytic activity of this material is attributed to: (1) the high surface to volume ratio which leads to more active sites being exposed to reactants; (2) the strong surface binding of the Au nanoparticle to the Au(I) complexes, which enhances both the stability and the catalytic activity of these complexes.

STRUCTURAL AND FUNCTIONAL CONSEQUENCES OF CIRCULAR PERMUTATION ON THE ACTIVE SITE OF OLD YELLOW ENZYME.

PubMed

Daugherty, Ashley B; Horton, John R; Cheng, Xiaodong; Lutz, Stefan

2015-02-06

Circular permutation of the NADPH-dependent oxidoreductase Old Yellow Enzyme from Saccharomyces pastorianus (OYE1) can significantly enhance the enzyme's catalytic performance. Termini relocation into four regions of the protein (sectors I-IV) near the active site has proven effective in altering enzyme function. To better understand the structural consequences and rationalize the observed functional gains in these OYE1 variants, we selected representatives from sectors I-III for further characterization by biophysical methods and X-ray crystallography. These investigations not only show trends in enzyme stability and quaternary structure as a function of termini location, but also provide a possible explanation for the catalytic gains in our top-performing OYE variant (new N-terminus at residue 303; sector III). Crystallographic analysis indicates that termini relocation into sector III affects the loop β6 region (amino acid positions: 290-310) of OYE1 which forms a lid over the active site. Peptide backbone cleavage greatly enhances local flexibility, effectively converting the loop into a tether and consequently increasing the environmental exposure of the active site. Interestingly, such active site remodeling does not negatively impact the enzyme's activity and stereoselectivity, nor does it perturb the conformation of other key active site residues with the exception of Y375. These observations were confirmed in truncation experiments, deleting all residues of the loop β6 region in our OYE variant. Intrigued by the finding that circular permutation leaves most of the key catalytic residues unchanged, we also tested OYE permutants for possible additive or synergistic effects of amino acid substitutions. Distinct functional changes in these OYE variants were detected upon mutations at W116, known in native OYE1 to cause inversion of diastereo-selectivity for ( S )-carvone reduction. Our findings demonstrate the contribution of loop β6 toward determining the stereoselectivity of OYE1, an important insight for future OYE engineering efforts.

Structural and Functional Consequences of Circular Permutation on the Active Site of Old Yellow Enzyme

DOE PAGES

Daugherty, Ashley B.; Horton, John R.; Cheng, Xiaodong; ...

2014-12-09

Circular permutation of the NADPH-dependent oxidoreductase Old Yellow Enzyme from Saccharomyces pastorianus (OYE1) can significantly enhance the enzyme’s catalytic performance. Termini relocation into four regions of the protein (sectors I–IV) near the active site has proven effective in altering enzyme function. To better understand the structural consequences and rationalize the observed functional gains in these OYE1 variants, we selected representatives from sectors I–III for further characterization by biophysical methods and X-ray crystallography. These investigations not only show trends in enzyme stability and quaternary structure as a function of termini location but also provide a possible explanation for the catalytic gainsmore » in our top-performing OYE variant (new N-terminus at residue 303; sector III). Crystallographic analysis indicates that termini relocation into sector III affects the loop β6 region (amino acid positions: 290–310) of OYE1, which forms a lid over the active site. Peptide backbone cleavage greatly enhances local flexibility, effectively converting the loop into a tether and consequently increasing the environmental exposure of the active site. Interestingly, such an active site remodeling does not negatively impact the enzyme’s activity and stereoselectivity; neither does it perturb the conformation of other key active site residues with the exception of Y375. These observations were confirmed in truncation experiments, deleting all residues of the loop β6 region in our OYE variant. Intrigued by the finding that circular permutation leaves most of the key catalytic residues unchanged, we also tested OYE permutants for possible additive or synergistic effects of amino acid substitutions. Distinct functional changes in these OYE variants were detected upon mutations at W116, known in native OYE1 to cause inversion of diastereoselectivity for (S)-carvone reduction. In conclusion, our findings demonstrate the contribution of loop β6 toward determining the stereoselectivity of OYE1, an important insight for future OYE engineering efforts.« less

Structural and biochemical characterization of glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum.

PubMed

Michikawa, Mari; Ichinose, Hitomi; Momma, Mitsuru; Biely, Peter; Jongkees, Seino; Yoshida, Makoto; Kotake, Toshihisa; Tsumuraya, Yoichi; Withers, Stephen G; Fujimoto, Zui; Kaneko, Satoshi

2012-04-20

We present the first structure of a glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum, both as a product complex with β-D-glucuronic acid (GlcA) and as its trapped covalent 2-fluoroglucuronyl intermediate. This enzyme consists of a catalytic (β/α)(8)-barrel domain and a β-domain with irregular Greek key motifs that is of unknown function. The enzyme showed β-glucuronidase activity and trace levels of β-glucosidase and β-xylosidase activities. In conjunction with mutagenesis studies, these structures identify the catalytic residues as Glu(173) (acid base) and Glu(287) (nucleophile), consistent with the retaining mechanism demonstrated by (1)H NMR analysis. Glu(45), Tyr(243), Tyr(292)-Gly(294), and Tyr(334) form the catalytic pocket and provide substrate discrimination. Consistent with this, the Y292A mutation, which affects the interaction between the main chains of Gln(293) and Gly(294) and the GlcA carboxyl group, resulted in significant loss of β-glucuronidase activity while retaining the side activities at wild-type levels. Likewise, although the β-glucuronidase activity of the Y334F mutant is ~200-fold lower (k(cat)/K(m)) than that of the wild-type enzyme, the β-glucosidase activity is actually 3 times higher and the β-xylosidase activity is only 2.5-fold lower than the equivalent parameters for wild type, consistent with a role for Tyr(334) in recognition of the C6 position of GlcA. The involvement of Glu(45) in discriminating against binding of the O-methyl group at the C4 position of GlcA is revealed in the fact that the E45D mutant hydrolyzes PNP-β-GlcA approximately 300-fold slower (k(cat)/K(m)) than does the wild-type enzyme, whereas 4-O-methyl-GlcA-containing oligosaccharides are hydrolyzed only 7-fold slower.

Structural and Biochemical Characterization of Glycoside Hydrolase Family 79 β-Glucuronidase from Acidobacterium capsulatum

PubMed Central

Michikawa, Mari; Ichinose, Hitomi; Momma, Mitsuru; Biely, Peter; Jongkees, Seino; Yoshida, Makoto; Kotake, Toshihisa; Tsumuraya, Yoichi; Withers, Stephen G.; Fujimoto, Zui; Kaneko, Satoshi

2012-01-01

We present the first structure of a glycoside hydrolase family 79 β-glucuronidase from Acidobacterium capsulatum, both as a product complex with β-d-glucuronic acid (GlcA) and as its trapped covalent 2-fluoroglucuronyl intermediate. This enzyme consists of a catalytic (β/α)8-barrel domain and a β-domain with irregular Greek key motifs that is of unknown function. The enzyme showed β-glucuronidase activity and trace levels of β-glucosidase and β-xylosidase activities. In conjunction with mutagenesis studies, these structures identify the catalytic residues as Glu173 (acid base) and Glu287 (nucleophile), consistent with the retaining mechanism demonstrated by 1H NMR analysis. Glu45, Tyr243, Tyr292–Gly294, and Tyr334 form the catalytic pocket and provide substrate discrimination. Consistent with this, the Y292A mutation, which affects the interaction between the main chains of Gln293 and Gly294 and the GlcA carboxyl group, resulted in significant loss of β-glucuronidase activity while retaining the side activities at wild-type levels. Likewise, although the β-glucuronidase activity of the Y334F mutant is ∼200-fold lower (kcat/Km) than that of the wild-type enzyme, the β-glucosidase activity is actually 3 times higher and the β-xylosidase activity is only 2.5-fold lower than the equivalent parameters for wild type, consistent with a role for Tyr334 in recognition of the C6 position of GlcA. The involvement of Glu45 in discriminating against binding of the O-methyl group at the C4 position of GlcA is revealed in the fact that the E45D mutant hydrolyzes PNP-β-GlcA approximately 300-fold slower (kcat/Km) than does the wild-type enzyme, whereas 4-O-methyl-GlcA-containing oligosaccharides are hydrolyzed only 7-fold slower. PMID:22367201

Efficient catalytic decomposition of formic acid for the selective generation of H2 and H/D exchange with a water-soluble rhodium complex in aqueous solution.

PubMed

Fukuzumi, Shunichi; Kobayashi, Takeshi; Suenobu, Tomoyoshi

2008-01-01

Formic acid (HCOOH) decomposes efficiently to afford H2 and CO2 selectively in the presence of a catalytic amount of a water-soluble rhodium aqua complex, [Rh(III)(Cp*)(bpy)(H2O)]2+ (Cp*=pentamethylcyclopentadienyl, bpy=2,2'-bipyridine) in aqueous solution at 298 K. No CO was produced in this catalytic decomposition of HCOOH. The decomposition rate reached a maximum value at pH 3.8. No deterioration of the catalyst was observed during the catalytic decomposition of HCOOH, and the catalytic activity remained the same for the repeated addition of HCOOH. The rhodium-hydride complex was detected as the catalytic active species that undergoes efficient H/D exchange with water. When the catalytic decomposition of HCOOH was performed in D2O, D2 was produced selectively. Such an efficient H/D exchange and the observation of a deuterium kinetic isotope effect in the catalytic decomposition of DCOOH in H2O provide valuable mechanistic insight into this efficient and selective decomposition process.

Investigations into the development of catalytic activity in anti-acetylcholinesterase idiotypic and anti-idiotypic antibodies.

PubMed

Johnson, Glynis; Moore, Samuel W

2009-01-01

We have previously described anti-acetylcholinesterase antibodies that display acetylcholinesterase-like catalytic activity. No evidence of contaminating enzymes was found, and the antibodies are kinetically and apparently structurally distinct from both acetylcholinesterase (AChE) and butyrylcholinesterase. We have also mimicked the antibody catalytic sites in anti-anti-idiotypic (Ab3) antibodies. Independently from us, similar acetylcholinesterase-like antibodies have been raised as anti-idiotypic (Ab2) antibodies against a non-catalytic anti-acetylcholinesterase antibody, AE-2. In this paper, we describe an epitope analysis, using synthetic peptides in ELISA and competition ELISA, and a peptide array, of five catalytic anti-acetylcholinesterase antibodies (Ab1s), three catalytic Ab3s, as well as antibody AE-2 and a non-catalytic Ab2. The catalytic Ab1s and Ab3s recognized three Pro- and Gly-containing sequences ((40)PPMGPRRFL, (78)PGFEGTE, and (258)PPGGTGGNDTELVAC) on the AChE surface. As these sequences do not adjoin in the AChE structure, recognition would appear to be due to cross-reaction. This was confirmed by the observation that the sequences superimpose structurally. The non-catalytic antibodies, AE-2 and the Ab2, recognized AChE's peripheral anionic site (PAS), in particular, the sequence (70)YQYVD, which contains two of the site's residues. The crystal structure of the AChE tetramer (Bourne et al., 1999) shows direct interaction and high complementarity between the (257)CPPGGTGGNDTELVAC sequence and the PAS. Antibodies recognizing the sequence and the PAS may, in turn, be complementary; this may account for the apparent paradox of catalytic development in both Ab1s and Ab2s. The PAS binds, but does not hydrolyze, substrate. The catalytic Ab1s, therefore, recognize a site that may function as a substrate analog, and this, together with the presence of an Arg-Glu salt bridge in the epitope, suggests mechanisms whereby catalytic activity may have developed. In conclusion, the development of AChE-like catalytic activity in anti-AChE Ab1s and Ab2s appears to be the result of a combination of structural complementarity to a substrate-binding site, charge complementarity to a salt bridge, and specific structural peculiarities of the AChE molecule. Copyright 2008 John Wiley & Sons, Ltd.

Enhanced catalytic activity through the tuning of micropore environment and supercritical CO2 processing: Al(porphyrin)-based porous organic polymers for the degradation of a nerve agent simulant.

PubMed

Totten, Ryan K; Kim, Ye-Seong; Weston, Mitchell H; Farha, Omar K; Hupp, Joseph T; Nguyen, SonBinh T

2013-08-14

An Al(porphyrin) functionalized with a large axial ligand was incorporated into a porous organic polymer (POP) using a cobalt-catalyzed acetylene trimerization strategy. Removal of the axial ligand afforded a microporous POP that is catalytically active in the methanolysis of a nerve agent simulant. Supercritical CO2 processing of the POP dramatically increased the pore size and volume, allowing for significantly higher catalytic activities.

Molecular Evolution of Human PON to Design Enhanced Catalytic Efficiency for Hydrolysis of Nerve Agents

DTIC Science & Technology

2011-12-01

8   C.   Catalytic activity of evolved variants with GA ................................................................. 11   D...several variants of rePON1 with enhanced activity towards a racemic mixture of CMP-Coumarin by screening ‘neutral drift’ libraries of rePON1 (e.g. 1G3, 2G9...22. The most active variant was 3B3, which had ~250-fold higher catalytic efficiency (kcat/Km 20x106 M-1min-1) compared to the wild-type-like

Alcohol conversion

DOEpatents

Wachs, Israel E.; Cai, Yeping

2002-01-01

Preparing an aldehyde from an alcohol by contacting the alcohol in the presence of oxygen with a catalyst prepared by contacting an intimate mixture containing metal oxide support particles and particles of a catalytically active metal oxide from Groups VA, VIA, or VIIA, with a gaseous stream containing an alcohol to cause metal oxide from the discrete catalytically active metal oxide particles to migrate to the metal oxide support particles and to form a monolayer of catalytically active metal oxide on said metal oxide support particles.

Extraction and Inhibition of Enzymatic Activity of Botulinum Neurotoxins/A1, /A2, and /A3 by a Panel of Monoclonal Anti-BoNT/A Antibodies

DTIC Science & Technology

2009-04-01

triplicate and results were averaged. MS Detection A master mix was created consisting of 9 parts matrix solution (alpha-cyano-4-hydroxy cinnamic acid ...thus, do not inhibit the catalytic activity. Another feature of BoNT/A is that it exhibits genetic and amino acid variance within the toxin type, or...less amino acid variance [23] and this variance has been reported to affect binding of the toxin to anti-BoNT/A mAbs [24]. For these reasons, it is

Plant Hexokinases are Multifaceted Proteins.

PubMed

Aguilera-Alvarado, G Paulina; Sánchez-Nieto, Sobeida

2017-07-01

Sugars are the main carbon and energy source in cells, but they can also act as signaling molecules that affect the whole plant life cycle. Certain tissues can produce sugars and supply them to others, and this plant tissue heterogeneity makes sugar signaling a highly complex process that requires elements capable of perceiving changes in sugar concentrations among different tissues, cell compartments and developmental stages. In plants, the regulatory effects of glucose (Glc) have been the most studied to date. The first Glc sensor identified in plants was hexokinase (HXK), which is currently recognized as a dual-function protein. In addition to its catalytic activity, this enzyme can also repress the expression of some photosynthetic genes in response to high internal Glc concentrations. Additionally, the catalytic activity of HXKs has a profound impact on cell metabolism and other sugar signaling pathways that depend on phosphorylated hexoses and intermediate glycolytic products. HXKs are the only proteins that are able to phosphorylate Glc in plants, since no evidence has been provided to date concerning the existence of a glucokinase. Moreover, the intracellular localization of HXKs seems to be crucial to their activity and sensor functions. Recently, two new and surprising functions have been described for HXKs. In this review, we discuss the versatility of HXKs in regard to their catalytic and glucose sensor activities, intracellular location, protein-protein and hormone interactions, as well as how these HXK characteristics influence plant growth and development, in an effort to understand this enzyme's role in improving plant productivity. © The Author 2017. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oup.com.

Intramolecular proton shuttle supports not only catalytic but also noncatalytic function of carbonic anhydrase II

PubMed Central

Becker, Holger M.; Klier, Michael; Schüler, Christina; McKenna, Robert; Deitmer, Joachim W.

2011-01-01

Carbonic anhydrases (CAs) catalyze the reversible hydration of CO2 to HCO3− and H+. The rate-limiting step in this reaction is the shuttle of protons between the catalytic center of the enzyme and the bulk solution. In carbonic anhydrase II (CAII), the fastest and most wide-spread isoform, this H+ shuttle is facilitated by the side chain of His64, whereas CA isoforms such as carbonic anhydrase III (CAIII), which lack such a shuttle, have only low catalytic activity in vitro. By using heterologous protein expression in Xenopus oocytes, we tested the role of this intramolecular H+ shuttle on CA activity in an intact cell. The data revealed that CAIII, shown in vitro to have ∼1,000-fold reduced activity as compared with CAII, displays significant catalytic activity in the intact cell. Furthermore, we tested the hypothesis that the H+ shuttle in CAII itself can facilitate transport activity of the monocarboxylate transporters 1 and 4 (MCT1/4) independent of catalytic activity. Our results show that His64 is essential for the enhancement of lactate transport via MCT1/4, because a mutation of this residue to alanine (CAII-H64A) abolishes the CAII-induced increase in MCT1/4 activity. However, injection of 4-methylimidazole, which acts as an exogenous H+ donor/acceptor, can restore the ability of CAII-H64A to enhance transport activity of MCT1/4. These findings support the hypothesis that the H+ shuttle in CAII not only facilitates CAII catalytic activity but also can enhance activity of acid-/base-transporting proteins such as MCT1/4 in a direct, noncatalytic manner, possibly by acting as an “H+-collecting antenna.” PMID:21282642

In situ Mössbauer investigation of iron oxide catalyst in water gas shift reaction - Impact of oxyreduction potential and temperature

NASA Astrophysics Data System (ADS)

Cherkezova-Zheleva, Z.; Mitov, I.

2010-03-01

The aim of the study is to obtain the exact state of iron oxide catalyst active phase in reaction conditions, as well as the correlation between the active phase and catalytic properties of iron-containing catalysts. In situ Mössbauer spectroscopy is the major investigation technique. It is established that the change of reaction conditions (temperature and gas reaction mixture) lead to redistribution of the relative weight of spectra components and influence mainly tetrahedrally and octahedrally coordinated cations in Fe3O4 phase. It was concluded, that the active sites of the catalyst in studied reaction are probably pairs of Fe3++Fe2+-(Fe2.5+) ions, i.e. the mixed valance iron ions. The obtained catalytic activity can be explained with combination of the natural thermo-activated and catalytically induced electron exchange and better synchronizing of oxidation and reduction steps of the catalytic reaction.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2014-05-27

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2014-10-28

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2015-04-14

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Methods of increasing secretion of polypeptides having biological activity

DOEpatents

Merino, Sandra

2013-10-01

The present invention relates to methods for producing a secreted polypeptide having biological activity, comprising: (a) transforming a fungal host cell with a fusion protein construct encoding a fusion protein, which comprises: (i) a first polynucleotide encoding a signal peptide; (ii) a second polynucleotide encoding at least a catalytic domain of an endoglucanase or a portion thereof; and (iii) a third polynucleotide encoding at least a catalytic domain of a polypeptide having biological activity; wherein the signal peptide and at least the catalytic domain of the endoglucanase increases secretion of the polypeptide having biological activity compared to the absence of at least the catalytic domain of the endoglucanase; (b) cultivating the transformed fungal host cell under conditions suitable for production of the fusion protein; and (c) recovering the fusion protein, a component thereof, or a combination thereof, having biological activity, from the cultivation medium.

Fluorescence and room temperature activity of Y₂O₃:(Eu³⁺,Au³⁺)/palygorskite nanocomposite.

PubMed

He, Xi; Yang, Huaming

2015-01-28

The fluorescence and room temperature activity of a palygorskite supported Y2O3:(Eu(3+),Au(3+)) nanocomposite were investigated to design a fluorescence-indicated catalyst. The effects of Au(3+) doping on the structure and surface properties of the host material were systematically characterized. The fluorescence intensity of Y2O3:Eu(3+) was affected by Au(3+) doping, which was related to the crystallinity of Y2O3. Excess Au(3+) ions were segregated to the host surface and reduced to metallic Au. The local symmetry of Eu(3+) was reduced by Au(3+) doping, which benefited the energy transfer between Eu(3+) and Au(3+). Energy absorbed by Eu(3+) was transferred from Au(3+) to metallic Au, where electrons were produced. These electrons were absorbed by O2 to change into O2(-), which acted as the oxidant for ortho-dichlorobenzene (o-DCB). The variation of fluorescence intensity during the catalytic reaction was observed. The room temperature catalytic activity of the nanocomposite under UV irradiation was revealed. The as-synthesized nanocomposite might have potential applications in environmental fields.

Effect of preparation procedures on catalytic activity and selectivity of copper-based mixed oxides in selective catalytic oxidation of ammonia into nitrogen and water vapour

NASA Astrophysics Data System (ADS)

Jabłońska, Magdalena; Nocuń, Marek; Gołąbek, Kinga; Palkovits, Regina

2017-11-01

The selective oxidation of ammonia into nitrogen and water vapour (NH3-SCO) was studied over Cu-Mg(Zn)-Al-(Zr) mixed metal oxides, obtained by coprecipitation and their subsequent calcination. The effect of acid-base properties of Cu-Mg-Al-Ox on catalytic activity was investigated by changing the Mg/Al molar ratio. Other Cu-containing oxides were prepared by rehydration of calcined Mg-Al hydrotalcite-like compounds or thermal decomposition of metal nitrate precursors. XRD, BET, NH3-TPD, H2-TPR, XPS, FTIR with adsorption of pyridine and CO as well as TEM techniques were used for catalysts characterization. The results of catalytic tests revealed a crucial role of easily reducible highly dispersed copper oxide species to obtain enhanced activity and N2 selectivity in NH3-SCO. The selective catalytic reduction of NO by NH3 (NH3-SCR) and in situ DRIFT of NH3 sorption indicated that NH3-SCO proceeds according to the internal selective catalytic reduction mechanism (i-SCR).

INVESTIGATION OF SELECTIVE CATALYTIC REDUCTION IMPACT ON MERCURY SPECIATION UNDER SIMULATED NOX EMISSION CONTROL CONDITIONS

EPA Science Inventory

Selective catalytic reduction (SCR) technology is being increasingly applied for controlling emissions of nitrogen oxides (NOx) from coal-fired boilers. Some recent field and pilot studies suggest that the operation of SCR could affect the chemical form of mercury in the coal com...

ZIF-67 incorporated with carbon derived from pomelo peels: A highly efficient bifunctional catalyst for oxygen reduction/evolution reactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hao; Yin, Feng-Xiang; Chen, Biao-Hua

Developing carbon catalyst materials using natural, abundant and renewable resources as precursors plays an increasingly important role in clean energy generation and environmental protection. In this work, N-doped pomelo-peel-derived carbon (NPC) materials were prepared using a widely available food waste-pomelo peels and melamine. The synthetic NPC exhibits well-defined porosities and a highly doped-N content (e.g. 6.38 at% for NPC-2), therefore affords excellent oxygen reduction reaction (ORR) catalytic activities in alkaline electrolytes. NPC was further integrated with ZIF-67 to form ZIF-67@NPC hybrids through solvothermal reactions. The hybrid catalysts show substantially enhanced ORR catalytic activities comparable to that of commercial 20 wamore » Pt/C. Furthermore, the catalysts also exhibit excellent oxygen evolution reaction (OER) catalytic activities. Among all prepared ZIF-67@NPC hybrids, the optimal composition with ZIF-67 to NPC ratio of 2:1 exhibits the best ORR and OER bifunctional catalytic performance and the smallest Delta E (E-OER@10 mA cm(-2)-E-ORR@-1 mA cm(-2)) value of 0.79 V. The catalyst also demonstrated desirable 4-electron transfer pathways and superior catalytic stabilities. The Co-N-4 in ZIF-67, electrochemical active surface area, and the strong interactions between ZIF-67 and NPC are attributed as the main contributors to the bifunctional catalytic activities. These factors act synergistically, resulting in substantially enhanced bifunctional catalytic activities and stabilities; consequently, this hybrid catalyst is among the best of the reported bifunctional electrocatalysts and is promising for use in metal-air batteries and fuel cells. (C) 2016 Elsevier B.V. All rights reserved.« less

Enzymatic and antisense effects of a specific anti-Ki-ras ribozyme in vitro and in cell culture.

PubMed Central

Giannini, C D; Roth, W K; Piiper, A; Zeuzem, S

1999-01-01

Due to their mode of action, ribozymes show antisense effects in addition to their specific cleavage activity. In the present study we investigated whether a hammerhead ribozyme is capable of cleaving mutated Ki-ras mRNA in a pancreatic carcinoma cell line and whether antisense effects contribute to the activity of the ribozyme. A 2[prime]-O-allyl modified hammerhead ribozyme was designed to cleave specifically the mutated form of the Ki- ras mRNA (GUU motif in codon 12). The activity was monitored by RT-PCR on Ki- ras RNA expression by determination of the relative amount of wild type to mutant Ki-ras mRNA, by 5-bromo-2[prime]-deoxy-uridine incorporation on cell proliferation and by colony formation in soft agar on malignancy in the human pancreatic adenocarcinoma cell line CFPAC-1, which is heterozygous for the Ki-ras mutation. A catalytically inactive ribozyme was used as control to differentiate between antisense and cleavage activity and a ribozyme with random guide sequences as negative control. The catalytically active anti-Ki-ras ribozyme was at least 2-fold more potent in decreasing cellular Ki-ras mRNA levels, inhibiting cell proliferation and colony formation in soft agar than the catalytically inactive ribozyme. The catalytically active anti-Ki-ras ribozyme, but not the catalytically inactive or random ribozyme, increased the ratio of wild type to mutated Ki-ras mRNA in CFPAC-1 cells. In conclusion, both cleavage activity and antisense effects contribute to the activity of the catalytically active anti-Ki-ras hammerhead ribozyme. Specific ribozymes might be useful in the treatment of pancreatic carcinomas containing an oncogenic GTT mutation in codon 12 of the Ki-ras gene. PMID:10373591

A Facile synthesis of superparamagnetic Fe3O4 nanofibers with superior peroxidase-like catalytic activity for sensitive colorimetric detection of L-cysteine

NASA Astrophysics Data System (ADS)

Chen, Sihui; Chi, Maoqiang; Zhu, Yun; Gao, Mu; Wang, Ce; Lu, Xiaofeng

2018-05-01

Superaramagnetic Fe3O4 nanomaterials are good candidates as enzyme mimics due to their excellent catalytic activity, high stability and facile synthesis. However, the morphology of Fe3O4 nanomaterials has much influence on their enzyme-like catalytic activity. In this work, we have developed a simple polymer-assisted thermochemical reduction approach to prepare Fe3O4 nanofibers for peroxidase-like catalytic applications. The as-prepared Fe3O4 nanofibers show a higher catalytic activity than commercial Fe3O4 nanoparticles. The steady-state kinetic assay result shows that the Michaelis-Menten constant value of the as-obtained Fe3O4 nanofibers is similar to that of horseradish peroxidase (HRP), indicating their superior affinity to the 3,3‧,5,5‧-tetramethylbenzidine (TMB) and H2O2 substrate. Based on the outstanding catalytic activity, a sensing platform for the detection of L-cysteine has been performed and the limit of detection is as low as 0.028 μM. In addition, an excellent selectivity toward L-cysteine over other types of amino acids, glucose and metal ions has been achieved as well. This work offers an original means for the fabrication of superparamagnetic Fe3O4 nanofibers and demonstrates their delightful potential applications in the fields of biosensing, environmental monitoring, and medical diagnostics.

Bimetallic Cu-Ni nanoparticles supported on activated carbon for catalytic oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Kimi, Melody; Jaidie, Mohd Muazmil Hadi; Pang, Suh Cem

2018-01-01

A series of bimetallic copper-nickel (CuNix, x = 0.1, 0.2, 0.5 and 1) nanoparticles supported on activated carbon (AC) were prepared by deposition-precipitation method for the oxidation of benzyl alcohol to benzaldehyde using hydrogen peroxide as oxidising agent. Analyses by means of X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) confirmed that Cu and Ni was successfully added on the surface of activated carbon. CuNi1/AC showed the best catalytic activity for the oxidation of benzyl alcohols to the corresponding aldehyde within a short reaction period at 80 °C. The catalytic performance is significantly enhanced by the addition of equal amount of Ni as compared to the monometallic counterpart. This result indicates the synergistic effect between Ni and Cu particles in the catalytic oxidation reaction.

Mechanistic Studies on the Copper-Catalyzed N-Arylation of Amides

PubMed Central

Strieter, Eric R.; Bhayana, Brijesh; Buchwald, Stephen L.

2009-01-01

The copper-catalyzed N-arylation of amides, i.e., the Goldberg reaction, is an efficient method for the construction of products relevant to both industry and academic settings. Herein, we present mechanistic details concerning the catalytic and stoichiometric N-arylation of amides. In the context of the catalytic reaction, our findings reveal the importance of chelating diamine ligands in controlling the concentration of the active catalytic species. The consistency between the catalytic and stoichiometric results suggest that the activation of aryl halides occurs through a 1,2-diamine-ligated copper(I) amidate complex. Kinetic studies on the stoichiometric N-arylation of aryl iodides using 1,2-diamine ligated Cu(I) amidates also provide insights into the mechanism of aryl halide activation. PMID:19072233

Abiotic stress and phytohormones affect enzymic activity of 1-O-(indole-3-acetyl)-β-d-glucose: myo-inositol indoleacetyl transferase from rice (Oryza sativa).

PubMed

Ciarkowska, Anna; Ostrowski, Maciej; Jakubowska, Anna

2016-10-20

Indole-3-acetic acid (IAA) conjugation is a part of mechanism regulating free auxin concentration. 1-O-(indole-3-acetyl)-β-d-glucose: myo-inositol indoleacetyl transferase (IAInos synthase) is an enzyme involved in IAA-ester conjugates biosynthesis. Biotic and abiotic stress conditions can modulate auxin conjugates formation in plants. In this study, we investigated effect of plant hormones (IAA, ABA, SA and 2,4-D) and abiotic stress (drought and salt stress: 150mM NaCl and 300mM NaCl) on expression level and catalytic activity of rice IAInos synthase. Enzymic activity assay indicated that all tested phytohormones affected activity of IAInos synthase, but only ABA had inhibiting effect, while IAA, SA and 2,4-D activated the enzyme. Drought and salt stress induced with lower NaCl concentration resulted in decreased activity of IAInos synthase, but 300mM NaCl had no effect on the enzyme. Despite observed differences in enzymic activities, no changes of expression level, tested by semiquantitative RT-PCR and Western blot, were detected. Based on our results it has been supposed that plant hormones and stress conditions affect IAInos synthase activity on posttranslational level. Copyright © 2016 Elsevier GmbH. All rights reserved.

Real-time investigation of human topoisomerase I reaction kinetics using an optical sensor: a fast method for drug screening and determination of active enzyme concentrations

NASA Astrophysics Data System (ADS)

Kristoffersen, Emil L.; Jørgensen, Line A.; Franch, Oskar; Etzerodt, Michael; Frøhlich, Rikke; Bjergbæk, Lotte; Stougaard, Magnus; Ho, Yi-Ping; Knudsen, Birgitta R.

2015-05-01

Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment.Human DNA topoisomerase I (hTopI) is a nuclear enzyme that catalyzes relaxation of super helical tension that arises in the genome during essential DNA metabolic processes. This is accomplished through a common reaction mechanism shared among the type IB topoisomerase enzymes, including eukaryotic and poxvirus topoisomerase I. The mechanism of hTopI is specifically targeted in cancer treatment using camptothecin derivatives. These drugs convert the hTopI activity into a cellular poison, and hence the cytotoxic effects of camptothecin derivatives correlate with the hTopI activity. Therefore, fast and reliable techniques for high throughput measurements of hTopI activity are of high clinical interest. Here we demonstrate potential applications of a fluorophore-quencher based DNA sensor designed for measurement of hTopI cleavage-ligation activities, which are the catalytic steps affected by camptothecin. The kinetic analysis of the hTopI reaction with the DNA sensor exhibits a characteristic burst profile. This is the result of a two-step ping-pong reaction mechanism, where a fast first reaction, the one creating the signal, is followed by a slower second reaction necessary for completion of the catalytic cycle. Hence, the burst profile holds information about two reactions in the enzymatic mechanism. Moreover, it allows the amount of active enzyme in the reaction to be determined. The presented results pave the way for future high throughput drug screening and the potential of measuring active hTopI concentrations in clinical samples for individualized treatment. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr01474c

Poliovirus replication requires the N-terminus but not the catalytic Sec7 domain of ArfGEF GBF1.

PubMed

Belov, George A; Kovtunovych, Gennadiy; Jackson, Catherine L; Ehrenfeld, Ellie

2010-10-01

Viruses are intracellular parasites whose reproduction relies on factors provided by the host. The cellular protein GBF1 is critical for poliovirus replication. Here we show that the contribution of GBF1 to virus replication is different from its known activities in uninfected cells. Normally GBF1 activates the ADP-ribosylation factor (Arf) GTPases necessary for formation of COPI transport vesicles. GBF1 function is modulated by p115 and Rab1b. However, in polio-infected cells, p115 is degraded and neither p115 nor Rab1b knock-down affects virus replication. Poliovirus infection is very sensitive to brefeldin A (BFA), an inhibitor of Arf activation by GBF1. BFA targets the catalytic Sec7 domain of GBF1. Nevertheless the BFA block of polio replication is rescued by expression of only the N-terminal region of GBF1 lacking the Sec7 domain. Replication of BFA-resistant poliovirus in the presence of BFA is uncoupled from Arf activation but is dependent on GBF1. Thus the function(s) of this protein essential for viral replication can be separated from those required for cellular metabolism. © Published 2010. This article is a US Government work and is in the public domain in the USA.

Unraveling the differences of the hydrolytic activity of Trypanosoma cruzi trans-sialidase and Trypanosoma rangeli sialidase: a quantum mechanics-molecular mechanics modeling study.

PubMed

Bueren-Calabuig, Juan A; Pierdominici-Sottile, Gustavo; Roitberg, Adrian E

2014-06-05

Chagas' disease, also known as American trypanosomiasis, is a lethal, chronic disease that currently affects more than 10 million people in Central and South America. The trans-sialidase from Trypanosoma cruzi (T. cruzi, TcTS) is a crucial enzyme for the survival of this parasite: sialic acids from the host are transferred to the cell surface glycoproteins of the trypanosome, thereby evading the host's immune system. On the other hand, the sialidase of T. rangeli (TrSA), which shares 70% sequence identity with TcTS, is a strict hydrolase and shows no trans-sialidase activity. Therefore, TcTS and TrSA represent an excellent framework to understand how different catalytic activities can be achieved with extremely similar structures. By means of combined quantum mechanics-molecular mechanics (QM/MM, SCC-DFTB/Amberff99SB) calculations and umbrella sampling simulations, we investigated the hydrolysis mechanisms of TcTS and TrSA and computed the free energy profiles of these reactions. The results, together with our previous computational investigations, are able to explain the catalytic mechanism of sialidases and describe how subtle differences in the active site make TrSA a strict hydrolase and TcTS a more efficient trans-sialidase.

Influence of various carbon nano-forms as supports for Pt catalyst on proton exchange membrane fuel cell performance

NASA Astrophysics Data System (ADS)

Bharti, Abha; Cheruvally, Gouri

2017-08-01

In this study, we discuss the influence of various carbon supports for Pt on proton exchange membrane (PEM) fuel cell performance. Here, Pt supported on various carbon nano-forms [Pt/carbon black (Pt/CB), Pt/single-walled carbon nanotubes (Pt/SWCNT), Pt/multi-walled carbon nanotubes (Pt/MWCNT) and Pt/graphene (Pt/G)] are synthesized by a facile, single step, microwave-assisted, modified chemical reduction route. Their physical, chemical and electrochemical characteristics pertaining to oxygen reduction reaction (ORR) catalytic activity and stability in PEM fuel cell are studied in detail by various techniques and compared. The study shows that the different carbon supports does not significantly affect the Pt particle size during synthesis, but leads to different amount of defective sites in the carbon framework which influence both the availability of active metal nano-catalysts and metal-support interaction. In-situ electrochemical investigations reveal that the different carbon supports influence both ORR catalytic activity and stability of the catalyst. This is further corroborated by the demonstration of varying polarization characteristics on PEM fuel cell performance by different carbon supported Pt catalysts. This study reveals MWCNT as the most suitable carbon support for Pt catalyst, exhibiting high activity and stability for ORR in PEM fuel cell.

The Small Glutathione Peroxidase Mimic 5P May Represent a New Strategy for the Treatment of Liver Cancer.

PubMed

Yin, Juxin; Wang, Bingmei; Zhu, Xuejun; Qu, Xiaonan; Huang, Yi; Lv, Shaowu; Mu, Ying; Luo, Guimin

2017-09-08

Glutathione peroxidase (GPx) is an antioxidant protein containing selenium. Owing to the limitations of native GPx, considerable efforts have been made to develop GPx mimics. Here, a short 5-mer peptides (5P) was synthesized and characterized using matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Enzyme coupled assays were used to evaluate GPx activity. The cell viability and apoptosis of H22 cells were tested, and mice bearing H22 cell-derived tumors were used to determine the effects of 5P on tumor inhibition. In comparison with other enzyme models, 5P provided a suitable substrate with proper catalytic site positions, resulting in enhanced catalytic activity. In our mouse model, 5P showed excellent inhibition of tumor growth and improved immunity. In summary, our findings demonstrated the design and synthesis of the small 5P molecule, which inhibited tumor growth and improved immunity. Notably, 5P could inhibit tumor growth without affecting normal growth. Based on these advantages, the novel mimic may have several clinical applications.

The catalytic activity for ginkgolic acid biodegradation, homology modeling and molecular dynamic simulation of salicylic acid decarboxylase.

PubMed

Hu, Yanying; Hua, Qingyuan; Sun, Guojuan; Shi, Kunpeng; Zhang, Huitu; Zhao, Kai; Jia, Shiru; Dai, Yujie; Wu, Qingli

2018-05-02

The toxic ginkgolic acids are the main safety concern for the application of Ginkgo biloba. In this study, the degradation ability of salicylic acid decarboxylase (SDC) for ginkgolic acids was examined using ginkgolic acid C15:1 as a substrate. The results indicated that the content of ginkgolic acid C15:1 in Ginkgo biloba seeds was significantly decreased after 5 h treatment with SDC at 40 °Cand pH 5.5. In order to explore the structure of SDC and the interaction between SDC and substrates, homology modeling, molecular docking and molecular dynamics were performed. The results showed that SDC might also have a catalytic active center containing a Zn 2+ . Compared with the template structure of 2,6-dihydroxybenzoate decarboxylase, the residues surrounding the binding pocket, His10, Phe23 and Phe290, were replaced by Ala10, Tyr27 and Tyr301 in the homology constructed structure of SDC, respectively. These differences may significantly affect the substrates adaptability of SDC for salicylic acid derivatives. Copyright © 2018 Elsevier Ltd. All rights reserved.

Reversible Regulation of Catalytic Activity of Gold Nanoparticles with DNA Nanomachines

NASA Astrophysics Data System (ADS)

Zhou, Peipei; Jia, Sisi; Pan, Dun; Wang, Lihua; Gao, Jimin; Lu, Jianxin; Shi, Jiye; Tang, Zisheng; Liu, Huajie

2015-09-01

Reversible catalysis regulation has gained much attention and traditional strategies utilized reversible ligand coordination for switching catalyst’s conformations. However, it remains challenging to regulate the catalytic activity of metal nanoparticle-based catalysts. Herein, we report a new DNA nanomachine-driven reversible nano-shield strategy for circumventing this problem. The basic idea is based on the fact that the conformational change of surface-attached DNA nanomachines will cause the variation of the exposed surface active area on metal nanoparticles. As a proof-of-concept study, we immobilized G-rich DNA strands on gold nanoparticles (AuNPs) which have glucose oxidase (GOx) like activity. Through the reversible conformational change of the G-rich DNA between a flexible single-stranded form and a compact G-quadruplex form, the catalytic activity of AuNPs has been regulated reversibly for several cycles. This strategy is reliable and robust, which demonstrated the possibility of reversibly adjusting catalytic activity with external surface coverage switching, rather than coordination interactions.

Probing active cocaine vaccination performance through catalytic and noncatalytic hapten design.

PubMed

Cai, Xiaoqing; Whitfield, Timothy; Hixon, Mark S; Grant, Yanabel; Koob, George F; Janda, Kim D

2013-05-09

Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complementary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH (keyhole limpet hemocyannin) was found to elicit persistent high-titer, cocaine-specific antibodies and blunt cocaine-induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges, the vaccine's protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse.

Probing Active Cocaine Vaccination Performance through Catalytic and Noncatalytic Hapten Design

PubMed Central

Cai, Xiaoqing; Whitfield, Timothy; Hixon, Mark S.; Grant, Yanabel; Koob, George F.; Janda, Kim D.

2013-01-01

Presently, there are no FDA-approved medications to treat cocaine addiction. Active vaccination has emerged as one approach to intervene through the rapid sequestering of the circulating drug, thus terminating both psychoactive effects and drug toxicity. Herein, we report our efforts examining two complimentary, but mechanistically distinct active vaccines, i.e., noncatalytic and catalytic, for cocaine treatment. A cocaine-like hapten GNE and a cocaine transition-state analogue GNT were used to generate the active vaccines, respectively. GNE-KLH was found to elicit persistent high-titer, cocaine-specific antibodies, and blunt cocaine induced locomotor behaviors. Catalytic antibodies induced by GNT-KLH were also shown to produce potent titers and suppress locomotor response in mice; however, upon repeated cocaine challenges the vaccine’s protecting effects waned. In depth kinetic analysis suggested that loss of catalytic activity was due to antibody modification by cocaine. The work provides new insights for the development of active vaccines for the treatment of cocaine abuse. PMID:23627877

A competent catalytic active site is necessary for substrate induced dimer assembly in triosephosphate isomerase.

PubMed

Jimenez-Sandoval, Pedro; Vique-Sanchez, Jose Luis; Hidalgo, Marisol López; Velazquez-Juarez, Gilberto; Diaz-Quezada, Corina; Arroyo-Navarro, Luis Fernando; Moran, Gabriela Montero; Fattori, Juliana; Jessica Diaz-Salazar, A; Rudiño-Pinera, Enrique; Sotelo-Mundo, Rogerio; Figueira, Ana Carolina Migliorini; Lara-Gonzalez, Samuel; Benítez-Cardoza, Claudia G; Brieba, Luis G

2017-11-01

The protozoan parasite Trichomonas vaginalis contains two nearly identical triosephosphate isomerases (TvTIMs) that dissociate into stable monomers and dimerize upon substrate binding. Herein, we compare the role of the "ball and socket" and loop 3 interactions in substrate assisted dimer assembly in both TvTIMs. We found that point mutants at the "ball" are only 39 and 29-fold less catalytically active than their corresponding wild-type counterparts, whereas Δloop 3 deletions are 1502 and 9400-fold less active. Point and deletion mutants dissociate into stable monomers. However, point mutants assemble as catalytic competent dimers upon binding of the transition state substrate analog PGH, whereas loop 3 deletions remain monomeric. A comparison between crystal structures of point and loop 3 deletion monomeric mutants illustrates that the catalytic residues in point mutants and wild-type TvTIMs are maintained in the same orientation, whereas the catalytic residues in deletion mutants show an increase in thermal mobility and present structural disorder that may hamper their catalytic role. The high enzymatic activity present in monomeric point mutants correlates with the formation of dimeric TvTIMs upon substrate binding. In contrast, the low activity and lack of dimer assembly in deletion mutants suggests a role of loop 3 in promoting the formation of the active site as well as dimer assembly. Our results suggest that in TvTIMs the active site is assembled during dimerization and that the integrity of loop 3 and ball and socket residues is crucial to stabilize the dimer. Copyright © 2017 Elsevier B.V. All rights reserved.

CuNi NPs supported on MIL-101 as highly active catalysts for the hydrolysis of ammonia borane

NASA Astrophysics Data System (ADS)

Gao, Doudou; Zhang, Yuhong; Zhou, Liqun; Yang, Kunzhou

2018-01-01

The catalysts containing Cu, Ni bi-metallic nanoparticles were successfully synthesized by in-situ reduction of Cu2+ and Ni2+ salts into the highly porous and hydrothermally stable metal-organic framework MIL-101 via a simple liquid impregnation method. When the total amount of loading metal is 3 × 10-4 mol, Cu2Ni1@MIL-101 catalyst shows higher catalytic activity comparing to CuxNiy@MIL-101 with different molar ratio of Cu and Ni (x, y = 0, 0.5, 1.5, 2, 2.5, 3). Cu2Ni1@MIL-101 catalyst has the highest catalytic activity comparing to mono-metallic Cu and Ni counterparts and pure bi-metallic CuNi nanoparticles in hydrolytic dehydrogeneration of ammonia borane (AB) at room temperature. Additionally, in the hydrolysis reaction, the Cu2Ni1@MIL- 101 catalyst possesses excellent catalytic performances, which exhibit highly catalytic activity with turn over frequency (TOF) value of 20.9 mol H2 min-1 Cu mol-1 and a very low activation energy value of 32.2 kJ mol-1. The excellent catalytic activity has been successfully achieved thanks to the strong bi-metallic synergistic effects, uniform distribution of nanoparticles and the bi-functional effects between CuNi nanoparticles and the host of MIL-101. Moreover, the catalyst also displays satisfied durable stability after five cycles for the hydrolytically releasing H2 from AB. The non-noble metal catalysts have broad prospects for commercial applications in the field of hydrogen-stored materials due to the low prices and excellent catalytic activity.

The Bridge Helix of RNA polymerase acts as a central nanomechanical switchboard for coordinating catalysis and substrate movement.

PubMed

Weinzierl, Robert O J

2011-01-01

The availability of in vitro assembly systems to produce recombinant archaeal RNA polymerases (RNAPs) offers one of the most powerful experimental tools for investigating the still relatively poorly understood molecular mechanisms underlying RNAP function. Over the last few years, we pioneered new robot-based high-throughput mutagenesis approaches to study structure/function relationships within various domains surrounding the catalytic center. The Bridge Helix domain, which appears in numerous X-ray structures as a 35-amino-acid-long alpha helix, coordinates the concerted movement of several other domains during catalysis through kinking of two discrete molecular hinges. Mutations affecting these kinking mechanisms have a direct effect on the specific catalytic activity of RNAP and can in some instances more than double it. Molecular dynamics simulations have established themselves as exceptionally useful for providing additional insights and detailed models to explain the underlying structural motions.

Diabetes reversal by inhibition of the low molecular weight tyrosine phosphatase

PubMed Central

Stanford, Stephanie M; Aleshin, Alexander E; Zhang, Vida; Ardecky, Robert J; Hedrick, Michael P; Zou, Jiwen; Ganji, Santhi R.; Bliss, Matthew R; Yamamoto, Fusayo; Bobkov, Andrey A.; Kiselar, Janna; Liu, Yingge; Cadwell, Gregory W; Khare, Shilpi; Yu, Jinghua; Barquilla, Antonio; Chung, Thomas DY; Mustelin, Tomas; Schenk, Simon; Bankston, Laurie A; Liddington, Robert C; Pinkerton, Anthony B; Bottini, Nunzio

2017-01-01

Obesity-associated insulin resistance plays a central role in type 2 diabetes. As such, tyrosine phosphatases that dephosphorylate the insulin receptor (IR) are potential therapeutic targets. The low molecular weight protein tyrosine phosphatase (LMPTP) is a proposed IR phosphatase, yet its role in insulin signaling in vivo has not been defined. Here we show that global and liver-specific LMPTP deletion protects mice from high-fat diet-induced diabetes without affecting body weight. To examine the role of the catalytic activity of LMPTP, we developed a small-molecule inhibitor with a novel uncompetitive mechanism, a unique binding site at the opening of the catalytic pocket, and exquisite selectivity over other phosphatases. This inhibitor is orally bioavailable, increases liver IR phosphorylation in vivo, and reverses high-fat diet induced diabetes. Our findings suggest that LMPTP is a key promoter of insulin resistance and that LMPTP inhibitors would be beneficial for treating type 2 diabetes. PMID:28346406

Diabetes reversal by inhibition of the low-molecular-weight tyrosine phosphatase.

PubMed

Stanford, Stephanie M; Aleshin, Alexander E; Zhang, Vida; Ardecky, Robert J; Hedrick, Michael P; Zou, Jiwen; Ganji, Santhi R; Bliss, Matthew R; Yamamoto, Fusayo; Bobkov, Andrey A; Kiselar, Janna; Liu, Yingge; Cadwell, Gregory W; Khare, Shilpi; Yu, Jinghua; Barquilla, Antonio; Chung, Thomas D Y; Mustelin, Tomas; Schenk, Simon; Bankston, Laurie A; Liddington, Robert C; Pinkerton, Anthony B; Bottini, Nunzio

2017-06-01

Obesity-associated insulin resistance plays a central role in type 2 diabetes. As such, tyrosine phosphatases that dephosphorylate the insulin receptor (IR) are potential therapeutic targets. The low-molecular-weight protein tyrosine phosphatase (LMPTP) is a proposed IR phosphatase, yet its role in insulin signaling in vivo has not been defined. Here we show that global and liver-specific LMPTP deletion protects mice from high-fat diet-induced diabetes without affecting body weight. To examine the role of the catalytic activity of LMPTP, we developed a small-molecule inhibitor with a novel uncompetitive mechanism, a unique binding site at the opening of the catalytic pocket, and an exquisite selectivity over other phosphatases. This inhibitor is orally bioavailable, and it increases liver IR phosphorylation in vivo and reverses high-fat diet-induced diabetes. Our findings suggest that LMPTP is a key promoter of insulin resistance and that LMPTP inhibitors would be beneficial for treating type 2 diabetes.

Enhancing the Activity of Peptide-Based Artificial Hydrolase with Catalytic Ser/His/Asp Triad and Molecular Imprinting.

PubMed

Wang, Mengfan; Lv, Yuqi; Liu, Xiaojing; Qi, Wei; Su, Rongxin; He, Zhimin

2016-06-08

In this study, an artificial hydrolase was developed by combining the catalytic Ser/His/Asp triad with N-fluorenylmethoxycarbonyl diphenylalanine (Fmoc-FF), followed by coassembly of the peptides into nanofibers (CoA-HSD). The peptide-based nanofibers provide an ideal supramolecular framework to support the functional groups. Compared with the self-assembled catalytic nanofibers (SA-H), which contain only the catalytic histidine residue, the highest activity of CoA-HSD occurs when histidine, serine, and aspartate residues are at a ratio of 40:1:1. This indicates that the well-ordered nanofiber structure and the synergistic effects of serine and aspartate residues contribute to the enhancement in activity. Additionally, for the first time, molecular imprinting was applied to further enhance the activity of the peptide-based artificial enzyme (CoA-HSD). p-NPA was used as the molecular template to arrange the catalytic Ser/His/Asp triad residues in the proper orientation. As a result, the activity of imprinted coassembled CoA-HSD nanofibers is 7.86 times greater than that of nonimprinted CoA-HSD and 13.48 times that of SA-H.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Daugherty, Ashley B.; Horton, John R.; Cheng, Xiaodong

Circular permutation of the NADPH-dependent oxidoreductase Old Yellow Enzyme from Saccharomyces pastorianus (OYE1) can significantly enhance the enzyme’s catalytic performance. Termini relocation into four regions of the protein (sectors I–IV) near the active site has proven effective in altering enzyme function. To better understand the structural consequences and rationalize the observed functional gains in these OYE1 variants, we selected representatives from sectors I–III for further characterization by biophysical methods and X-ray crystallography. These investigations not only show trends in enzyme stability and quaternary structure as a function of termini location but also provide a possible explanation for the catalytic gainsmore » in our top-performing OYE variant (new N-terminus at residue 303; sector III). Crystallographic analysis indicates that termini relocation into sector III affects the loop β6 region (amino acid positions: 290–310) of OYE1, which forms a lid over the active site. Peptide backbone cleavage greatly enhances local flexibility, effectively converting the loop into a tether and consequently increasing the environmental exposure of the active site. Interestingly, such an active site remodeling does not negatively impact the enzyme’s activity and stereoselectivity; neither does it perturb the conformation of other key active site residues with the exception of Y375. These observations were confirmed in truncation experiments, deleting all residues of the loop β6 region in our OYE variant. Intrigued by the finding that circular permutation leaves most of the key catalytic residues unchanged, we also tested OYE permutants for possible additive or synergistic effects of amino acid substitutions. Distinct functional changes in these OYE variants were detected upon mutations at W116, known in native OYE1 to cause inversion of diastereoselectivity for (S)-carvone reduction. In conclusion, our findings demonstrate the contribution of loop β6 toward determining the stereoselectivity of OYE1, an important insight for future OYE engineering efforts.« less

High-temperature catalytically assisted combustion. Final report, 1 August 1981-31 July 1983

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bracco, F.V.; Royce, B.S.H.; Santavicca, D.A.

1983-07-31

Results of research on a two-dimensional, transient catalytic combustion model and on a high temperature perovskite catalyst are presented. A recently developed two-dimensional, transient model was used to study the ignition of carbon monoxide/air mixtures in a platinum-coated catalytic honeycomb. Comparisons between calculated and measured steady-state substrate temperature profiles and exhaust-gas compositions show good agreement. A platinum-doped perovskite catalyst proposed will exhibit low-temperature light off and high-temperature stability. Preliminary tests using a perovskite powder with 1 wt.% platinium are encouraging, showing very little change in surface activity when used with propane fuel. Variations in catalytic activity from sample to samplemore » were also found, and after extensive testing the cause of these variations could not be identified. However, preliminary tests using Fourier-transform infrared photoacoustic spectroscopy do indicate differences in the various catalyst samples that may be related to the difference in catalytic activity. The use of bench-top-oven and differential-scanning-calorimetry techniques for screening catalysts in terms of relative activity and aging characteristics were also demonstrated.« less

The chaperone role of the pyridoxal 5'-phosphate and its implications for rare diseases involving B6-dependent enzymes.

PubMed

Cellini, Barbara; Montioli, Riccardo; Oppici, Elisa; Astegno, Alessandra; Voltattorni, Carla Borri

2014-02-01

The biologically active form of the B6 vitamers is pyridoxal 5'-phosphate (PLP), which plays a coenzymatic role in several distinct enzymatic activities ranging from the synthesis, interconversion and degradation of amino acids to the replenishment of one-carbon units, synthesis and degradation of biogenic amines, synthesis of tetrapyrrolic compounds and metabolism of amino-sugars. In the catalytic process of PLP-dependent enzymes, the substrate amino acid forms a Schiff base with PLP and the electrophilicity of the PLP pyridine ring plays important roles in the subsequent catalytic steps. While the essential role of PLP in the acquisition of biological activity of many proteins is long recognized, the finding that some PLP-enzymes require the coenzyme for refolding in vitro points to an additional role of PLP as a chaperone in the folding process. Mutations in the genes encoding PLP-enzymes are causative of several rare inherited diseases. Patients affected by some of these diseases (AADC deficiency, cystathionuria, homocystinuria, gyrate atrophy, primary hyperoxaluria type 1, xanthurenic aciduria, X-linked sideroblastic anaemia) can benefit, although at different degrees, from the administration of pyridoxine, a PLP precursor. The effect of the coenzyme is not limited to mutations that affect the enzyme-coenzyme interaction, but also to those that cause folding defects, reinforcing the idea that PLP could play a chaperone role and improve the folding efficiency of misfolded variants. In this review, recent biochemical and cell biology studies highlighting the chaperoning activity of the coenzyme on folding-defective variants of PLP-enzymes associated with rare diseases are presented and discussed. Copyright © 2013 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Dynamics of the active site loops in catalyzing aminoacylation reaction in seryl and histidyl tRNA synthetases.

PubMed

Dutta, Saheb; Kundu, Soumya; Saha, Amrita; Nandi, Nilashis

2018-03-01

Aminoacylation reaction is the first step of protein biosynthesis. The catalytic reorganization at the active site of aminoacyl tRNA synthetases (aaRSs) is driven by the loop motions. There remain lacunae of understanding concerning the catalytic loop dynamics in aaRSs. We analyzed the functional loop dynamics in seryl tRNA synthetase from Methanopyrus kandleri ( mk SerRS) and histidyl tRNA synthetases from Thermus thermophilus ( tt HisRS), respectively, using molecular dynamics. Results confirm that the motif 2 loop and other active site loops are flexible spots within the catalytic domain. Catalytic residues of the loops form a network of interaction with the substrates to form a reactive state. The loops undergo transitions between closed state and open state and the relaxation of the constituent residues occurs in femtosecond to nanosecond time scale. Order parameters are higher for constituent catalytic residues which form a specific network of interaction with the substrates to form a reactive state compared to the Gly residues within the loop. The development of interaction is supported from mutation studies where the catalytic domain with mutated loop exhibits unfavorable binding energy with the substrates. During the open-close motion of the loops, the catalytic residues make relaxation by ultrafast librational motion as well as fast diffusive motion and subsequently relax rather slowly via slower diffusive motion. The Gly residues act as a hinge to facilitate the loop closing and opening by their faster relaxation behavior. The role of bound water is analyzed by comparing implicit solvent-based and explicit solvent-based simulations. Loops fail to form catalytically competent geometry in absence of water. The present result, for the first time reveals the nature of the active site loop dynamics in aaRS and their influence on catalysis.

Enhanced catalytic activity of the nanostructured Co-W-B film catalysts for hydrogen evolution from the hydrolysis of ammonia borane.

PubMed

Li, Chao; Wang, Dan; Wang, Yan; Li, Guode; Hu, Guijuan; Wu, Shiwei; Cao, Zhongqiu; Zhang, Ke

2018-08-15

In this work, nanostructured Co-W-B films are successfully synthesized on the foam sponge by electroless plating method and employed as the catalysts with enhanced catalytic activity towards hydrogen evolution from the hydrolysis of ammonia borane (NH 3 BH 3 , AB) at room temperature. The particle size of the as-prepared Co-W-B film catalysts is varied by adjusting the depositional pH value to identify the most suitable particle size for hydrogen evolution of AB hydrolysis. The Co-W-B film catalyst with the particle size of about 67.3 nm shows the highest catalytic activity and can reach a hydrogen generation rate of 3327.7 mL min -1 g cat -1 at 298 K. The activation energy of the hydrolysis reaction of AB is determined to be 32.2 kJ mol -1 . Remarkably, the as-obtained Co-W-B film is also a reusable catalyst preserving 78.4% of their initial catalytic activity even after 5 cycles in hydrolysis of AB at room temperature. Thus, the enhanced catalytic activity illustrates that the Co-W-B film is a promising catalyst for AB hydrolytic dehydrogenation in fuel cells and the related fields. Copyright © 2018 Elsevier Inc. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xue, Teng; Lin, Zhaoyang; Chiu, Chin-Yi

Metallic nanoparticles are emerging as an exciting class of heterogeneous catalysts with the potential advantages of exceptional activity, stability, recyclability, and easier separation than homogeneous catalysts. The traditional colloid nanoparticle syntheses usually involve strong surface binding ligands that could passivate the surface active sites and result in poor catalytic activity. The subsequent removal of surface ligands could reactivate the surface but often leads to metal ion leaching and/or severe Ostwald ripening with diminished catalytic activity or poor stability. Molecular ligand engineering represents a powerful strategy for the design of homogeneous molecular catalysts but is insufficiently explored for nanoparticle catalysts tomore » date. We report a systematic investigation on molecular ligand modulation of palladium (Pd) nanoparticle catalysts. Our studies show that β-functional groups of butyric acid ligand on Pd nanoparticles can significantly modulate the catalytic reaction process to modify the catalytic activity and stability for important aerobic reactions. With a β-hydroxybutyric acid ligand, the Pd nanoparticle catalysts exhibit exceptional catalytic activity and stability with an unsaturated turnover number (TON) >3000 for dehydrogenative oxidation of cyclohexenone to phenol, greatly exceeding that of homogeneous Pd(II) catalysts (TON, ~30). This study presents a systematic investigation of molecular ligand modulation of nanoparticle catalysts and could open up a new pathway toward the design and construction of highly efficient and robust heterogeneous catalysts through molecular ligand engineering.« less

Palladium-pyridyl catalytic films: a highly active and recyclable catalyst for hydrogenation of styrene under mild conditions.

PubMed

Gao, Shuiying; Li, Weijin; Cao, Rong

2015-03-01

Palladium-pyridyl catalytic films, (PdCl2/bpy)n, were created by alternating immersions of a substrate in PdCl2 and bpy (bpy=4, 4'-bipyridyl) solutions. The as-prepared (PdCl2/bpy)10 catalyst demonstrated a remarkable catalytic activity toward hydrogenation of styrene under mild conditions and the turnover frequency (TOF) is as high as 6944h(-1). Pd(II) ions of (PdCl2/bpy)n films are in situ reduced to Pd nanoparticles (NPs) during the hydrogenation of styrene process, which results in the catalytic activity of the films. The results of X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) further demonstrate that Pd(II) ions of (PdCl2/bpy)n films were gradually converted to Pd(0) states. The catalytic activity is related to bilayer numbers and the activity increases with the number of bilayers below 10 bilayers. The solid substrates coated with (PdCl2/bpy)n multilayer catalysts were easily removed from the reaction mixture without separation filtration. Moreover, (PdCl2/bpy)n catalysts were reused for 10 consecutive reactions without loss of activity. The present (PdCl2/bpy)n heterogeneous catalysts have the advantages of easy separation and good recyclability. Copyright © 2014 Elsevier Inc. All rights reserved.

Molecular and thermodynamic mechanisms of the chloride-dependent human angiotensin-I-converting enzyme (ACE).

PubMed

Yates, Christopher J; Masuyer, Geoffrey; Schwager, Sylva L U; Akif, Mohd; Sturrock, Edward D; Acharya, K Ravi

2014-01-17

Somatic angiotensin-converting enzyme (sACE), a key regulator of blood pressure and electrolyte fluid homeostasis, cleaves the vasoactive angiotensin-I, bradykinin, and a number of other physiologically relevant peptides. sACE consists of two homologous and catalytically active N- and C-domains, which display marked differences in substrate specificities and chloride activation. A series of single substitution mutants were generated and evaluated under varying chloride concentrations using isothermal titration calorimetry. The x-ray crystal structures of the mutants provided details on the chloride-dependent interactions with ACE. Chloride binding in the chloride 1 pocket of C-domain ACE was found to affect positioning of residues from the active site. Analysis of the chloride 2 pocket R522Q and R522K mutations revealed the key interactions with the catalytic site that are stabilized via chloride coordination of Arg(522). Substrate interactions in the S2 subsite were shown to affect chloride affinity in the chloride 2 pocket. The Glu(403)-Lys(118) salt bridge in C-domain ACE was shown to stabilize the hinge-bending region and reduce chloride affinity by constraining the chloride 2 pocket. This work demonstrated that substrate composition to the C-terminal side of the scissile bond as well as interactions of larger substrates in the S2 subsite moderate chloride affinity in the chloride 2 pocket of the ACE C-domain, providing a rationale for the substrate-selective nature of chloride dependence in ACE and how this varies between the N- and C-domains.

Molecular and Thermodynamic Mechanisms of the Chloride-dependent Human Angiotensin-I-converting Enzyme (ACE)*

PubMed Central

Yates, Christopher J.; Masuyer, Geoffrey; Schwager, Sylva L. U.; Akif, Mohd; Sturrock, Edward D.; Acharya, K. Ravi

2014-01-01

Somatic angiotensin-converting enzyme (sACE), a key regulator of blood pressure and electrolyte fluid homeostasis, cleaves the vasoactive angiotensin-I, bradykinin, and a number of other physiologically relevant peptides. sACE consists of two homologous and catalytically active N- and C-domains, which display marked differences in substrate specificities and chloride activation. A series of single substitution mutants were generated and evaluated under varying chloride concentrations using isothermal titration calorimetry. The x-ray crystal structures of the mutants provided details on the chloride-dependent interactions with ACE. Chloride binding in the chloride 1 pocket of C-domain ACE was found to affect positioning of residues from the active site. Analysis of the chloride 2 pocket R522Q and R522K mutations revealed the key interactions with the catalytic site that are stabilized via chloride coordination of Arg522. Substrate interactions in the S2 subsite were shown to affect chloride affinity in the chloride 2 pocket. The Glu403-Lys118 salt bridge in C-domain ACE was shown to stabilize the hinge-bending region and reduce chloride affinity by constraining the chloride 2 pocket. This work demonstrated that substrate composition to the C-terminal side of the scissile bond as well as interactions of larger substrates in the S2 subsite moderate chloride affinity in the chloride 2 pocket of the ACE C-domain, providing a rationale for the substrate-selective nature of chloride dependence in ACE and how this varies between the N- and C-domains. PMID:24297181

A single mutation in a tunnel to the active site changes the mechanism and kinetics of product release in haloalkane dehalogenase LinB.

PubMed

Biedermannová, Lada; Prokop, Zbyněk; Gora, Artur; Chovancová, Eva; Kovács, Mihály; Damborsky, Jiří; Wade, Rebecca C

2012-08-17

Many enzymes have buried active sites. The properties of the tunnels connecting the active site with bulk solvent affect ligand binding and unbinding and also the catalytic properties. Here, we investigate ligand passage in the haloalkane dehalogenase enzyme LinB and the effect of replacing leucine by a bulky tryptophan at a tunnel-lining position. Transient kinetic experiments show that the mutation significantly slows down the rate of product release. Moreover, the mechanism of bromide ion release is changed from a one-step process in the wild type enzyme to a two-step process in the mutant. The rate constant of bromide ion release corresponds to the overall steady-state turnover rate constant, suggesting that product release became the rate-limiting step of catalysis in the mutant. We explain the experimental findings by investigating the molecular details of the process computationally. Analysis of trajectories from molecular dynamics simulations with a tunnel detection software reveals differences in the tunnels available for ligand egress. Corresponding differences are seen in simulations of product egress using a specialized enhanced sampling technique. The differences in the free energy barriers for egress of a bromide ion obtained using potential of mean force calculations are in good agreement with the differences in rates obtained from the transient kinetic experiments. Interactions of the bromide ion with the introduced tryptophan are shown to affect the free energy barrier for its passage. The study demonstrates how the mechanism of an enzymatic catalytic cycle and reaction kinetics can be engineered by modification of protein tunnels.

Antiproliferative activity of guava leaf extract via inhibition of prostaglandin endoperoxide H synthase isoforms.

PubMed

Kawakami, Yuki; Nakamura, Tomomi; Hosokawa, Tomoko; Suzuki-Yamamoto, Toshiko; Yamashita, Hiromi; Kimoto, Masumi; Tsuji, Hideaki; Yoshida, Hideki; Hada, Takahiko; Takahashi, Yoshitaka

2009-01-01

Prostaglandin endoperoxide H synthase (PGHS) is a key enzyme for the synthesis of prostaglandins (PGs) which play important roles in inflammation and carcinogenesis. Because the extract from Psidium guajava is known to have a variety of beneficial effects on our body including the anti-inflammatory, antioxidative and antiproliferative activities, we investigated whether the extract inhibited the catalytic activity of the two PGHS isoforms using linoleic acid as an alternative substrate. The guava leaf extract inhibited the cyclooxygenase reaction of recombinant human PGHS-1 and PGHS-2 as assessed by conversion of linoleic acid to 9- and 13-hydroxyoctadecadienoic acids (HODEs). The guava leaf extract also inhibited the PG hydroperoxidase activity of PGHS-1, which was not affected by nonsteroidal anti-inflammatory drugs (NSAIDs). Quercetin which was one of the major components not only inhibited the cyclooxygenase activity of both isoforms but also partially inhibited the PG hydroperoxidase activity. Overexpression of human PGHS-1 and PGHS-2 in the human colon carcinoma cells increased the DNA synthesis rate as compared with mock-transfected cells which did not express any isoforms. The guava leaf extract not only inhibited the PGE(2) synthesis but also suppressed the DNA synthesis rate in the PGHS-1- and PGHS-2-expressing cells to the same level as mock-transfected cells. These results demonstrate the antiproliferative activity of the guava leaf extract which is at least in part caused by inhibition of the catalytic activity of PGHS isoforms.

Dynamic structural disorder in supported nanoscale catalysts

NASA Astrophysics Data System (ADS)

Rehr, J. J.; Vila, F. D.

2014-04-01

We investigate the origin and physical effects of "dynamic structural disorder" (DSD) in supported nano-scale catalysts. DSD refers to the intrinsic fluctuating, inhomogeneous structure of such nano-scale systems. In contrast to bulk materials, nano-scale systems exhibit substantial fluctuations in structure, charge, temperature, and other quantities, as well as large surface effects. The DSD is driven largely by the stochastic librational motion of the center of mass and fluxional bonding at the nanoparticle surface due to thermal coupling with the substrate. Our approach for calculating and understanding DSD is based on a combination of real-time density functional theory/molecular dynamics simulations, transient coupled-oscillator models, and statistical mechanics. This approach treats thermal and dynamic effects over multiple time-scales, and includes bond-stretching and -bending vibrations, and transient tethering to the substrate at longer ps time-scales. Potential effects on the catalytic properties of these clusters are briefly explored. Model calculations of molecule-cluster interactions and molecular dissociation reaction paths are presented in which the reactant molecules are adsorbed on the surface of dynamically sampled clusters. This model suggests that DSD can affect both the prefactors and distribution of energy barriers in reaction rates, and thus can significantly affect catalytic activity at the nano-scale.

Stoichiometric and Catalytic Scavengers as Protection Against Nerve Agent Toxicity: A Mini Review

DTIC Science & Technology

2007-01-01

signs of nerve agent toxicity following exposure . Assessments of motor activity , coordination, and acquisition of spatial memory were performed for 2...serious side occur before endogenous AChE is affected (approxi- effects if administered in the absence of cholinesterase mately 2 min after exposure to an...after guinea pigs of cholinesterase in the blood and the level of protec- were administered 60mg/kg of HuBuChE (-󈧎-fold tion against OP poisoning

Complexity and Challenges in Noncontact High Temperature Measurements in Microwave-Assisted Catalytic Reactors

PubMed Central

2017-01-01

The complexity and challenges in noncontact temperature measurements inside microwave-heated catalytic reactors are presented in this paper. A custom-designed microwave cavity has been used to focus the microwave field on the catalyst and enable monitoring of the temperature field in 2D. A methodology to study the temperature distribution in the catalytic bed by using a thermal camera in combination with a thermocouple for a heterogeneous catalytic reaction (methane dry reforming) under microwave heating has been demonstrated. The effects of various variables that affect the accuracy of temperature recordings are discussed in detail. The necessity of having at least one contact sensor, such as a thermocouple, or some other microwave transparent sensor, is recommended to keep track of the temperature changes occurring in the catalytic bed during the reaction under microwave heating. PMID:29170599

Recent Advances in Metal-Organic Frameworks for Heterogeneous Catalyzed Organic Transformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sabale, Sandip R.; Zheng, Jian; Vemuri, Venkata Rama Ses

2016-12-12

In this review, we have summarized the recent advances in MOF based heterogeneous catalytic chemistry. Catalytic performance of various configurations of MOFs such as active sites, post synthetic modification and MOF derived catalyst, has been summarized in the context of various organic transformation reactions. Post synthetic modification of MOFs via functionalization of organic linkers with active catalytic moieties was deliberated. Also, efficacy of carbonaceous catalysts derived from MOFs was discussed.

Clay catalyzed RNA synthesis under Martian conditions: Application for Mars return samples.

PubMed

Joshi, Prakash C; Dubey, Krishna; Aldersley, Michael F; Sausville, Meaghen

2015-06-26

Catalysis by montmorillonites clay minerals is regarded as a feasible mechanism for the abiotic production and polymerization of key biomolecules on early Earth. We have investigated a montmorillonite-catalyzed reaction of the 5'-phosphorimidazolide of nucleosides as a model to probe prebiotic synthesis of RNA-type oligomers. Here we show that this model is specific for the generation of RNA oligomers despite deoxy-mononucleotides adsorbing equally well onto the montmorillonite catalytic surfaces. Optimum catalytic activity was observed over a range of pH (6-9) and salinity (1 ± 0.2 M NaCl). When the weathering steps of early Earth that generated catalytic montmorillonite were modified to meet Martian soil conditions, the catalytic activity remained intact without altering the surface layer charge. Additionally, the formation of oligomers up to tetramer was detected using as little as 0.1 mg of Na⁺-montmorillonite, suggesting that the catalytic activity of a Martian clay return sample can be investigated with sub-milligram scale samples. Copyright © 2015 Elsevier Inc. All rights reserved.

Determination of a kinetic region in catalytic oxidation of carbon monoxide

NASA Technical Reports Server (NTRS)

Sultanov, M. Y.; Sadykhova, K. A.

1981-01-01

The catalytic activity of cupric oxide activated with ceric oxide in a braod interval of volumetric velocities was investigated. It was determined that for practical catalysts used in the diffuse region, dilution of the active substance by an inert diluent increases the effectiveness of the catalysts.

Catalytic and thermal cracking processes of waste cooking oil for bio-gasoline synthesis

NASA Astrophysics Data System (ADS)

Dewanto, Muhammad Andry Rizki; Januartrika, Aulia Azka; Dewajani, Heny; Budiman, Arief

2017-03-01

Non-renewable energy resources such as fossil fuels, and coal were depleted as the increase of global energy demand. Moreover, environmental aspect becomes a major concern which recommends people to utilize bio-based resources. Waste cooking oil is one of the economical sources for biofuel production and become the most used raw material for biodiesel production. However, the products formed during frying, can affect the trans-esterification reaction and the biodiesel properties. Therefore, it needs to convert low-quality cooking oil directly into biofuel by both thermal and catalytic cracking processes. Thermal and catalytic cracking sometimes are regarded as prospective bio-energy conversion processes. This research was carried out in the packed bed reactor equipped with 2 stages preheater with temperature of reactor was variated in the range of 450-550°C. At the same temperature, catalytic cracking had been involved in this experiment, using activated ZSM-5 catalyst with 1 cm in length. The organic liquid product was recovered by three stages of double pipe condensers. The composition of cracking products were analyzed using GC-MS instrument and the caloric contents were analyzed using Bomb calorimeter. The results reveal that ZSM-5 was highly selective toward aromatic and long aliphatic compounds formation. The percentage recovery of organic liquid product from the cracking process varies start from 8.31% and the optimal results was 54.08%. The highest heating value of liquid product was resulted from catalytic cracking process at temperature of 450°C with value of 10880.48 cal/gr and the highest product yield with 54.08% recovery was achieved from thermal cracking process with temperature of 450°C.

The performances of proto-type Ni/MH secondary batteries using Zr-based hydrogen storage alloys and filamentary type Ni

NASA Astrophysics Data System (ADS)

Lee, Sang-Min; Lee, Ho; Kim, Jin-Ho; Lee, Paul S.; Lee, Jai-Young

2001-04-01

For the purpose of developing a Zr-based Laves phase alloy with higher capacity and better performance for electrochemical application, extensive work has been carried out. After careful alloy design of ZrMn2-based hydrogen storage alloys through varying their stoichiometry by means of substituting or adding alloying elements, the Zr0.9Ti0.1(Mn0.7V0.5Ni1.4)0.92 with high capacity (392 mAh/g at the 0.25C) and improved performance (comparable to that of commercialized AB5 type alloy) was developed. Another endeavor was made to improve the poor activation property and the low rate capability of the developed Zr-based Laves phase alloy for commercialization. The combination method of hot-immersion and slow-charging was introduced. It was found that electrode activation was greatly improved after hot immersion at 80°C for 12h followed by charging at 0.05C. The effects of this method are discussed in comparison with other activation methods. The combination method was successfully applied to the formation process of 80 Ah Ni/MH cells. A series of systematic investigations has been rendered to analyze the inner cell pressure characteristics of a sealed type Ni-MH battery. It was found that the increase of inner cell pressure in the sealed type Ni/MH battery of the above-mentioned Zr-Ti-Mn-V-Ni alloy was mainly due to the accumulation of oxygen gas during charge/discharge cycling. The fact identified that the surface catalytic activity was affected more dominantly by the oxygen recombination reaction than the reaction surface area was also identified. In order to improve the surface catalytic activity of a Zr-Ti-Mn-V-Ni alloy, which is closely related to the inner pressure behavior in a sealed cell, the electrode was fabricated by mixing the alloy with Cu powder and a filamentary type of Ni and replacing 75% of the carbon black with them; thus, the inner cell pressure rarely increases with cycles due to the active gas recombination reaction. Measurements of the surface area of the electrode and the surface catalytic activity showed that the surface catalytic activity for the oxygen recombination reaction was greatly improved by the addition of Cu powder and the filamentary type of Ni. Finally, we have collaborated with Hyundai Motors Company on fabrication of the 80Ah cells for Electric Vehicles and evaluated the cell performance.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jack Preiss

Conversion of the Potato tuber ADP-glucose Pyrophopshorylase Regulatory Subunit into a Catalytic Subunit. ADP-glucose synthesis, a rate-limiting reaction in starch synthesis, is catalyzed by ADP-glucose pyrophosphorylase (ADPGlc PPase). The enzyme in plants is allosterically activated by 3-phosphoglycerate (3PGA) and inhibited by inorganic phosphate (Pi) and is composed of two subunits as a heterotetramer, a2b2. Subunit a is the catalytic subunit and subunit b is designated as the regulatory subunit.The b subunit increases the affinty of the activator for the catalytic subunit. Recent results have shown that the subunits are derived from the same ancestor subunit as the regulatory subunit canmore » be converted to a catalytically subunit via mutation of just two amino acids. Lys44 and Thr54 in the large subunit from potato tuber were converted to the homologous catalytic subunit residues, Arg33 and Lys43. The activity of the large subunit mutants cannot be readily tested with a co-expressed wild-type small (catalytic) subunit because of the intrinsic activity of the latter. We co-expressed the regulatory-subunit mutants with SmallD145N, an inactive S subunit in which the catalytic Asp145 was mutated. The activity of the small (catalytic) subunit was reduced more than three orders of magnitude. Coexpression of the L subunit double mutant LargeK44R/T54K with SmallD145N generated an enzyme with considerable activity, 10% and 18% of the wildtype enzyme, in the ADP-glucose synthetic and pyrophosphorolytic direction, respectively. Replacement of those two residues in the small subunit by the homologous amino acids in the L subunits (mutations R33K and K43T) decreased the activity one and two orders of magnitude. The wild-type enzyme and SmallD145NLargeK44R/T54K had very similar kinetic properties indicating that the substrate site has been conserved. The fact that only two mutations in the L subunit restored enzyme activity is very strong evidence that the large subunit is derived from the catalytic ancestor. Previous results showed that Asp145 in the small subunit of the wild-type is essential for catalysis, whereas the homologous Asp160 in the Large WT subunit is not. However, in this study, mutation D160N or D160E in the LK44R/T54K subunit abolished the activity, which shows the ancestral essential role of this residue and confirms that the catalysis of SmallD145NLarge K44R/T54K occurs in the L(b) subunit. A phylogenetic tree of the ADP-Glc PPases present in photosynthetic eukaryotes also sheds information about the origin of the subunits. The tree showed that plant Small and Large subunits can be divided into two and four distinct groups, respectively. The two main groups of S subunits are from dicot and monocot plants, whereas Large subunit groups correlate better with their documented tissue expression. The first Large-subunit group is generally expressed in photosynthetic tissues and comprises Large subunits from dicots and monocots. Group II displays a broader expression pattern, whereas groups III and IV are expressed in storage organs (roots, stems, tubers, seeds). Subunits from group III are only from dicot plants, whereas group IV are seed-specific subunits from monocots. These last two groups stem from the same branch of the phylogenetic tree and split before monocot and dicot separation. Thus few as two mutations turned the L subunit from Solanum tuberosum catalytic, showing that L and S subunits share a common catalytic ancestor, rather than a non-catalytic one. The L subunit evolved to have a regulatory role, lost catalytic residues more than 130 million years ago before monocots and dicots diverged, and preserved, possibly as a byproduct, the active site domain.« less

Radiofrequency treatment enhances the catalytic function of an immobilized nanobiohybrid catalyst

NASA Astrophysics Data System (ADS)

San, Boi Hoa; Ha, Eun-Ju; Paik, Hyun-Jong; Kim, Kyeong Kyu

2014-05-01

Biocatalysis, the use of enzymes in chemical transformation, has undergone intensive development for a wide range of applications. As such, maximizing the functionality of enzymes for biocatalysis is a major priority to enable industrial use. To date, many innovative technologies have been developed to address the future demand of enzymes for these purposes, but maximizing the catalytic activity of enzymes remains a challenge. In this study, we demonstrated that the functionality of a nanobiocatalyst could be enhanced by combining immobilization and radiofrequency (RF) treatment. Aminopeptidase PepA-encapsulating 2 nm platinum nanoparticles (PepA-PtNPs) with the catalytic activities of hydrolysis and hydrogenation were employed as multifunctional nanobiocatalysts. Immobilizing the nanobiocatalysts in a hydrogel using metal chelation significantly enhanced their functionalities, including catalytic power, thermal-stability, pH tolerance, organic solvent tolerance, and reusability. Most importantly, RF treatment of the hydrogel-immobilized PepA-PtNPs increased their catalytic power by 2.5 fold greater than the immobilized PepA. Our findings indicate that the catalytic activities and functionalities of PepA-PtNPs are greatly enhanced by the combination of hydrogel-immobilization and RF treatment. Based on our findings, we propose that RF treatment of nanobiohybrid catalysts immobilized on the bulk hydrogel represents a new strategy for achieving efficient biocatalysis.Biocatalysis, the use of enzymes in chemical transformation, has undergone intensive development for a wide range of applications. As such, maximizing the functionality of enzymes for biocatalysis is a major priority to enable industrial use. To date, many innovative technologies have been developed to address the future demand of enzymes for these purposes, but maximizing the catalytic activity of enzymes remains a challenge. In this study, we demonstrated that the functionality of a nanobiocatalyst could be enhanced by combining immobilization and radiofrequency (RF) treatment. Aminopeptidase PepA-encapsulating 2 nm platinum nanoparticles (PepA-PtNPs) with the catalytic activities of hydrolysis and hydrogenation were employed as multifunctional nanobiocatalysts. Immobilizing the nanobiocatalysts in a hydrogel using metal chelation significantly enhanced their functionalities, including catalytic power, thermal-stability, pH tolerance, organic solvent tolerance, and reusability. Most importantly, RF treatment of the hydrogel-immobilized PepA-PtNPs increased their catalytic power by 2.5 fold greater than the immobilized PepA. Our findings indicate that the catalytic activities and functionalities of PepA-PtNPs are greatly enhanced by the combination of hydrogel-immobilization and RF treatment. Based on our findings, we propose that RF treatment of nanobiohybrid catalysts immobilized on the bulk hydrogel represents a new strategy for achieving efficient biocatalysis. Electronic supplementary information (ESI) available. See DOI: 10.1039/c4nr00407h

Antiacanthain A: New proteases isolated from Bromelia antiacantha Bertol. (Bromeliaceae).

PubMed

Vallés, Diego; Cantera, Ana M B

2018-07-01

Crude extract (CE) from pulp of Bromelia antiacantha Bertol. mature fruit, contains at least 3 cysteine proteases with proteolytic activity. By single step cation exchange chromatography (Hi-trap SP-HP) of partially purified CE, the protease with the lowest pI, Antiacanthain A (AntA), was isolated. It showed maximum activity at pH9, and 75% of remaining activity was maintained over a wide pH range (pH6-10). The AntA activity exhibits a constant increase up to 70°C. Maintains almost 100% of its activity at 45 at pH6 and 9. A 60% of AntA was active by titration with specific inhibitor, E64. Amidasic activity was studied with pyroglutamyl-phenyl-leucyl-paranitroaniline (PFLNA) substrate having higher AntA catalytic efficiency of (k cat /K m =470s -1 M -1 ) relative to stem bromelain (k cat /K m =305s -1 M -1 ). Esterase activity using p-nitrophenyl esters of N-α-CBZ-l-Lysine (z-L-LysONp) showed a 10-fold higher catalytic efficiency for AntA (k cat /K m =6376s -1 M -1 ) relative to stem bromelain (k cat /K m =688s -1 M -1 ). Incubation with 8M Urea did not affect AntA activity and remained unchanged for 18h, with 6M GndHCl resulted in a 41% decrease in activity after 30min incubation, maintained this activity 18h. AntA exhibits high sequence identity with proteases of the Bromeliaceae family. Copyright © 2018 Elsevier B.V. All rights reserved.

Effect of nitrogen-containing impurities on the activity of perovskitic catalysts for the catalytic combustion of methane.

PubMed

Buchneva, Olga; Gallo, Alessandro; Rossetti, Ilenia

2012-11-05

LaMnO(3), either pure or doped with 10 mol % Sr, has been prepared by flame pyrolysis in nanostructured form. Such catalysts have been tested for the catalytic flameless combustion of methane, achieving very high catalytic activity. The resistance toward poisoning by some model N-containing impurities has been checked in order to assess the possibility of operating the flameless catalytic combustion with biogas, possibly contaminated by S- or N-based compounds. This would be a significant improvement from the environmental point of view because the application of catalytic combustion to gas turbines would couple improved energy conversion efficiency and negligible noxious emissions, while the use of biogas would open the way to energy production from a renewable source by means of very efficient technologies. A different behavior has been observed for the two catalysts; namely, the undoped sample was more or less heavily poisoned, whereas the Sr-doped sample showed slightly increasing activity upon dosage of N-containing compounds. A possible reaction mechanism has been suggested, based on the initial oxidation of the organic backbone, with the formation of NO. The latter may adsorb more or less strongly depending on the availability of surface oxygen vacancies (i.e., depending on doping). Decomposition of NO may leave additional activated oxygen species on the surface, available for low-temperature methane oxidation and so improving the catalytic performance.

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

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

2006-08-01

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

Pt@Ag and Pd@Ag core/shell nanoparticles for catalytic degradation of Congo red in aqueous solution.

PubMed

Salem, Mohamed A; Bakr, Eman A; El-Attar, Heba G

2018-01-05

Platinum/silver (Pt@Ag) and palladium/silver (Pd@Ag) core/shell NPs have been synthesized in two steps reaction using the citrate method. The progress of nanoparticle formation was followed by the UV/Vis spectroscopy. Transmission electron microscopy revealed spherical shaped core/shell nanoparticles with average particle diameter 32.17nm for Pt@Ag and 8.8nm for Pd@Ag. The core/shell NPs were further characterized by FT-IR and XRD. Reductive degradation of the Congo red dye was chosen to demonstrate the excellent catalytic activity of these core/shell nanostructures. The nanocatalysts act as electron mediators for the transfer of electrons from the reducing agent (NaBH 4 ) to the dye molecules. Effect of reaction parameters such as nanocatalyst dose, dye and NaBH 4 concentrations on the dye degradation was investigated. A comparison between the catalytic activities of both nanocatalysts was made to realize which of them the best in catalytic performance. Pd@Ag was the higher in catalytic activity over Pt@Ag. Such greater activity is originated from the smaller particle size and larger surface area. Pd@Ag nanocatalyst was catalytically stable through four subsequent reaction runs under the utilized reaction conditions. These findings can thus be considered as possible economical alternative for environmental safety against water pollution by dyes. Copyright © 2017. Published by Elsevier B.V.

Pt@Ag and Pd@Ag core/shell nanoparticles for catalytic degradation of Congo red in aqueous solution

NASA Astrophysics Data System (ADS)

Salem, Mohamed A.; Bakr, Eman A.; El-Attar, Heba G.

2018-01-01

Platinum/silver (Pt@Ag) and palladium/silver (Pd@Ag) core/shell NPs have been synthesized in two steps reaction using the citrate method. The progress of nanoparticle formation was followed by the UV/Vis spectroscopy. Transmission electron microscopy revealed spherical shaped core/shell nanoparticles with average particle diameter 32.17 nm for Pt@Ag and 8.8 nm for Pd@Ag. The core/shell NPs were further characterized by FT-IR and XRD. Reductive degradation of the Congo red dye was chosen to demonstrate the excellent catalytic activity of these core/shell nanostructures. The nanocatalysts act as electron mediators for the transfer of electrons from the reducing agent (NaBH4) to the dye molecules. Effect of reaction parameters such as nanocatalyst dose, dye and NaBH4 concentrations on the dye degradation was investigated. A comparison between the catalytic activities of both nanocatalysts was made to realize which of them the best in catalytic performance. Pd@Ag was the higher in catalytic activity over Pt@Ag. Such greater activity is originated from the smaller particle size and larger surface area. Pd@Ag nanocatalyst was catalytically stable through four subsequent reaction runs under the utilized reaction conditions. These findings can thus be considered as possible economical alternative for environmental safety against water pollution by dyes.

VUV photo-oxidation of gaseous benzene combined with ozone-assisted catalytic oxidation: Effect on transition metal catalyst

NASA Astrophysics Data System (ADS)

Huang, Haibao; Lu, Haoxian; Zhan, Yujie; Liu, Gaoyuan; Feng, Qiuyu; Huang, Huiling; Wu, Muyan; Ye, Xinguo

2017-01-01

Volatile organic compounds (VOCs) cause the major air pollution concern. In this study, a series of ZSM-5 supported transition metals were prepared by impregnation method. They were combined with vacuum UV (VUV) photo-oxidation in a continuous-flow packed-bed reactor and used for the degradation of benzene, a typical toxic VOCs. Compared with VUV photo-oxidation alone, the introduction of catalysts can greatly enhance benzene oxidation under the help of O3, the by-products from VUV irradiation, via ozone-assisted catalytic oxidation (OZCO). The catalytic activity of transition metals towards benzene oxidation followed the order: Mn > Co > Cu > Ni > Fe. Mn achieved the best catalytic activity due to the strongest capability for O3 catalytic decomposition and utilization. Benzene and O3 removal efficiency reached as high as 97% and 100% after 360 min, respectively. O3 was catalytically decomposed, generating highly reactive oxidants such as rad OH and rad O for benzene oxidation.

Release of the glycosylphosphatidylinositol-anchored enzyme ecto-5'-nucleotidase by phospholipase C: catalytic activation and modulation by the lipid bilayer.

PubMed Central

Lehto, M T; Sharom, F J

1998-01-01

Many hydrolytic enzymes are attached to the extracellular face of the plasma membrane of eukaryotic cells by a glycosylphosphatidylinositol (GPI) anchor. Little is currently known about the consequences for enzyme function of anchor cleavage by phosphatidylinositol-specific phospholipase C. We have examined this question for the GPI-anchored protein 5'-nucleotidase (5'-ribonucleotide phosphohydrolase; EC 3.1.3.5), both in the native lymphocyte plasma membrane, and following purification and reconstitution into defined lipid bilayer vesicles, using Bacillus thuringiensis phosphatidylinositol-specific phospholipase C (PI-PLC). Membrane-bound, detergent-solubilized and cleaved 5'-nucleotidase all obeyed Michaelis-Menten kinetics, with a Km for 5'-AMP in the range 11-16 microM. The GPI anchor was removed from essentially all 5'-nucleotidase molecules, indicating that there is no phospholipase-resistant pool of enzyme. However, the phospholipase was much less efficient at cleaving the GPI anchor when 5'-nucleotidase was present in detergent solution, dimyristoyl phosphatidylcholine, egg phosphatidylethanolamine and sphingomyelin, compared with the native plasma membrane, egg phosphatidylcholine and a sphingolipid/cholesterol-rich mixture. Lipid molecular properties and bilayer packing may affect the ability of PI-PLC to gain access to the GPI anchor. Catalytic activation, characterized by an increase in Vmax, was observed following PI-PLC cleavage of reconstituted 5'-nucleotidase from vesicles of several different lipids. The highest degree of activation was noted for 5'-nucleotidase in egg phosphatidylethanolamine. An increase in Vmax was also noted for a sphingolipid/cholesterol-rich mixture, the native plasma membrane and egg phosphatidylcholine, whereas vesicles of sphingomyelin and dimyristoyl phosphatidylcholine showed little activation. Km generally remained unchanged following cleavage, except in the case of the sphingolipid/cholesterol-rich mixture. Insertion of the GPI anchor into a lipid bilayer appears to reduce the catalytic efficiency of 5'-nucleotidase, possibly via a conformational change in the enzyme, and activity is restored on release from the membrane. PMID:9576857

Rubisco Activity: Effects of Drought Stress

PubMed Central

PARRY, MARTIN A. J.; ANDRALOJC, P. JOHN; KHAN, SHAHNAZ; LEA, PETER J.; KEYS, ALFRED J.

2002-01-01

Ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) activity is modulated in vivo either by reaction with CO2 and Mg2+ to carbamylate a lysine residue in the catalytic site, or by the binding of inhibitors within the catalytic site. Binding of inhibitors blocks either activity or the carbamylation of the lysine residue that is essential for activity. At night, in many species, 2‐carboxyarabinitol‐1‐phosphate (CA1P) is formed which binds tightly to Rubisco, inhibiting catalytic activity. Recent work has shown that tight‐binding inhibitors can also decrease Rubisco activity in the light and contribute to the regulation of Rubisco activity. Here we determine the influence that such inhibitors of Rubisco exert on catalytic activity during drought stress. In tobacco plants, ‘total Rubisco activity’, i.e. the activity following pre‐incubation with CO2 and Mg2+, was positively correlated with leaf relative water content. However, ‘total Rubisco activity’ in extracts from leaves with low water potential increased markedly when tightly bound inhibitors were removed, thus increasing the number of catalytic sites available. This suggests that in tobacco the decrease of Rubisco activity under drought stress is not primarily the result of changes in activation by CO2 and Mg2+ but due rather to the presence of tight‐binding inhibitors. The amounts of inhibitor present in leaves of droughted tobacco based on the decrease in Rubisco activity per mg soluble protein were usually much greater than the amounts of the known inhibitors (CA1P and ‘daytime inhibitor’) that can be recovered in acid extracts. Alternative explanations for the difference between maximal and total activities are discussed. PMID:12102509

A minimal kinetic model for a viral DNA packaging machine.

PubMed

Yang, Qin; Catalano, Carlos Enrique

2004-01-20

Terminase enzymes are common to both eukaryotic and prokaryotic double-stranded DNA viruses. These enzymes possess ATPase and nuclease activities that work in concert to "package" a viral genome into an empty procapsid, and it is likely that terminase enzymes from disparate viruses utilize a common packaging mechanism. Bacteriophage lambda terminase possesses a site-specific nuclease activity, a so-called helicase activity, a DNA translocase activity, and multiple ATPase catalytic sites that function to package viral DNA. Allosteric interactions between the multiple catalytic sites have been reported. This study probes these catalytic interactions using enzyme kinetic, photoaffinity labeling, and vanadate inhibition studies. The ensemble of data forms the basis for a minimal kinetic model for lambda terminase. The model incorporates an ADP-driven conformational reorganization of the terminase subunits assembled on viral DNA, which is central to the activation of a catalytically competent packaging machine. The proposed model provides a unifying mechanism for allosteric interaction between the multiple catalytic sites of the holoenzyme and explains much of the kinetic data in the literature. Given that similar packaging mechanisms have been proposed for viruses as dissimilar as lambda and the herpes viruses, the model may find general utility in our global understanding of the enzymology of virus assembly.

Histone Deacetylase Adaptation in Single Ventricle Heart Disease and a Young Animal Model of Right Ventricular Hypertrophy

PubMed Central

Blakeslee, Weston W.; Demos-Davies, Kimberly M.; Lemon, Douglas D.; Lutter, Katharina M.; Cavasin, Maria A.; Payne, Sam; Nunley, Karin; Long, Carlin S.; McKinsey, Timothy A.; Miyamoto, Shelley D.

2017-01-01

Background Histone deacetylase (HDAC) inhibitors are promising therapeutics for various forms of cardiac disease. The purpose of this study was to assess cardiac HDAC catalytic activity and expression in children with single ventricle heart disease of right ventricular morphology (SV), as well as in a rodent model of right ventricular hypertrophy (RVH). Methods Homogenates of RV explants from non-failing controls and SV children were assayed for HDAC catalytic activity and HDAC isoform expression. Postnatal 1-day old rat pups were placed in hypoxic conditions and echocardiographic analysis, gene expression, HDAC catalytic activity and isoform expression studies of the RV were performed. Results Class I, IIa, and IIb HDAC catalytic activity and protein expression were elevated in hearts of SV children. Hypoxic neonatal rats demonstrated RVH, abnormal gene expression and elevated class I and class IIb HDAC catalytic activity and protein expression in the RV compared to control. Conclusions These data suggest that myocardial HDAC adaptations occur in the SV heart and could represent a novel therapeutic target. While further characterization of the hypoxic neonatal rat is needed, this animal model may be suitable for pre-clinical investigations of pediatric RV disease and could serve as a useful model for future mechanistic studies. PMID:28549058

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

DOE PAGES

Zugic, Branko; Wang, Lucun; Heine, Christian; ...

2016-12-19

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

Dynamic restructuring drives catalytic activity on nanoporous gold–silver alloy catalysts

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zugic, Branko; Wang, Lucun; Heine, Christian

Bimetallic, nanostructured materials hold promise for improving catalyst activity and selectivity, yet little is known about the dynamic compositional and structural changes that these systems undergo during pretreatment that leads to efficient catalyst function. Here we use ozone-activated silver–gold alloys in the form of nanoporous gold as a case study to demonstrate the dynamic behaviour of bimetallic systems during activation to produce a functioning catalyst. We show that it is these dynamic changes that give rise to the observed catalytic activity. Advanced in situ electron microscopy and X-ray photoelectron spectroscopy are used to demonstrate that major restructuring and compositional changesmore » occur along the path to catalytic function for selective alcohol oxidation. Transient kinetic measurements correlate the restructuring to three types of oxygen on the surface. The direct influence of changes in surface silver concentration and restructuring at the nanoscale on oxidation activity is demonstrated. Finally, our results demonstrate that characterization of these dynamic changes is necessary to unlock the full potential of bimetallic catalytic materials.« less

Direct 3D Printing of Catalytically Active Structures

DOE PAGES

Manzano, J. Sebastian; Weinstein, Zachary B.; Sadow, Aaron D.; ...

2017-09-22

3D printing of materials with active functional groups can provide custom-designed structures that promote chemical conversions. Catalytically active architectures were produced by photopolymerizing bifunctional molecules using a commercial stereolithographic 3D printer. Functionalities in the monomers included a polymerizable vinyl group to assemble the 3D structures and a secondary group to provide them with active sites. The 3D-printed architectures containing accessible carboxylic acid, amine, and copper carboxylate functionalities were catalytically active for the Mannich, aldol, and Huisgen cycloaddition reactions, respectively. The functional groups in the 3D-printed structures were also amenable to post-printing chemical modification. And as proof of principle, chemically activemore » cuvette adaptors were 3D printed and used to measure in situ the kinetics of a heterogeneously catalyzed Mannich reaction in a conventional solution spectrophotometer. In addition, 3D-printed millifluidic devices with catalytically active copper carboxylate complexes were used to promote azide-alkyne cycloaddition under flow conditions. The importance of controlling the 3D architecture of the millifluidic devices was evidenced by enhancing reaction conversion upon increasing the complexity of the 3D prints.« less

Direct 3D Printing of Catalytically Active Structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Manzano, J. Sebastian; Weinstein, Zachary B.; Sadow, Aaron D.

3D printing of materials with active functional groups can provide custom-designed structures that promote chemical conversions. Catalytically active architectures were produced by photopolymerizing bifunctional molecules using a commercial stereolithographic 3D printer. Functionalities in the monomers included a polymerizable vinyl group to assemble the 3D structures and a secondary group to provide them with active sites. The 3D-printed architectures containing accessible carboxylic acid, amine, and copper carboxylate functionalities were catalytically active for the Mannich, aldol, and Huisgen cycloaddition reactions, respectively. The functional groups in the 3D-printed structures were also amenable to post-printing chemical modification. And as proof of principle, chemically activemore » cuvette adaptors were 3D printed and used to measure in situ the kinetics of a heterogeneously catalyzed Mannich reaction in a conventional solution spectrophotometer. In addition, 3D-printed millifluidic devices with catalytically active copper carboxylate complexes were used to promote azide-alkyne cycloaddition under flow conditions. The importance of controlling the 3D architecture of the millifluidic devices was evidenced by enhancing reaction conversion upon increasing the complexity of the 3D prints.« less

Advanced treatment of biologically pretreated coal chemical industry wastewater using the catalytic ozonation process combined with a gas-liquid-solid internal circulating fluidized bed reactor.

PubMed

Li, Zhipeng; Liu, Feng; You, Hong; Ding, Yi; Yao, Jie; Jin, Chao

2018-04-01

This paper investigated the performance of the combined system of catalytic ozonation and the gas-liquid-solid internal circulating fluidized bed reactor for the advanced treatment of biologically pretreated coal chemical industry wastewater (CCIW). The results indicated that with ozonation alone for 60min, the removal efficiency of chemical oxygen demand (COD) could reach 34%. The introduction of activated carbon, pumice, γ-Al 2 O 3 carriers improved the removal performance of COD, and the removal efficiency was increased by 8.6%, 4.2%, 2%, respectively. Supported with Mn, the catalytic performance of activated carbon and γ-Al 2 O 3 were improved significantly with COD removal efficiencies of 46.5% and 41.3%, respectively; however, the promotion effect of pumice supported with Mn was insignificant. Activated carbon supported with Mn had the best catalytic performance. The catalytic ozonation combined system of MnO X /activated carbon could keep ozone concentration at a lower level in the liquid phase, and promote the transfer of ozone from the gas phase to the liquid phase to improve ozonation efficiency.

Atomic Scale Analysis of the Enhanced Electro- and Photo-Catalytic Activity in High-Index Faceted Porous NiO Nanowires

NASA Astrophysics Data System (ADS)

Shen, Meng; Han, Ali; Wang, Xijun; Ro, Yun Goo; Kargar, Alireza; Lin, Yue; Guo, Hua; Du, Pingwu; Jiang, Jun; Zhang, Jingyu; Dayeh, Shadi A.; Xiang, Bin

2015-02-01

Catalysts play a significant role in clean renewable hydrogen fuel generation through water splitting reaction as the surface of most semiconductors proper for water splitting has poor performance for hydrogen gas evolution. The catalytic performance strongly depends on the atomic arrangement at the surface, which necessitates the correlation of the surface structure to the catalytic activity in well-controlled catalyst surfaces. Herein, we report a novel catalytic performance of simple-synthesized porous NiO nanowires (NWs) as catalyst/co-catalyst for the hydrogen evolution reaction (HER). The correlation of catalytic activity and atomic/surface structure is investigated by detailed high resolution transmission electron microscopy (HRTEM) exhibiting a strong dependence of NiO NW photo- and electrocatalytic HER performance on the density of exposed high-index-facet (HIF) atoms, which corroborates with theoretical calculations. Significantly, the optimized porous NiO NWs offer long-term electrocatalytic stability of over one day and 45 times higher photocatalytic hydrogen production compared to commercial NiO nanoparticles. Our results open new perspectives in the search for the development of structurally stable and chemically active semiconductor-based catalysts for cost-effective and efficient hydrogen fuel production at large scale.

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.

Near-IR MCD of the nonheme ferrous active site in naphthalene 1,2-dioxygenase: correlation to crystallography and structural insight into the mechanism of Rieske dioxygenases.

PubMed

Ohta, Takehiro; Chakrabarty, Sarmistha; Lipscomb, John D; Solomon, Edward I

2008-02-06

Near-IR MCD and variable temperature, variable field (VTVH) MCD have been applied to naphthalene 1,2-dioxygenase (NDO) to describe the coordination geometry and electronic structure of the mononuclear nonheme ferrous catalytic site in the resting and substrate-bound forms with the Rieske 2Fe2S cluster oxidized and reduced. The structural results are correlated with the crystallographic studies of NDO and other related Rieske nonheme iron oxygenases to develop molecular level insights into the structure/function correlation for this class of enzymes. The MCD data for resting NDO with the Rieske center oxidized indicate the presence of a six-coordinate high-spin ferrous site with a weak axial ligand which becomes more tightly coordinated when the Rieske center is reduced. Binding of naphthalene to resting NDO (Rieske oxidized and reduced) converts the six-coordinate sites into five-coordinate (5c) sites with elimination of a water ligand. In the Rieske oxidized form the 5c sites are square pyramidal but transform to a 1:2 mixture of trigonal bipyramial/square pyramidal sites when the Rieske center is reduced. Thus the geometric and electronic structure of the catalytic site in the presence of substrate can be significantly affected by the redox state of the Rieske center. The catalytic ferrous site is primed for the O2 reaction when substrate is bound in the active site in the presence of the reduced Rieske site. These structural changes ensure that two electrons and the substrate are present before the binding and activation of O2, which avoids the uncontrolled formation and release of reactive oxygen species.

A dynamic mechanism for allosteric activation of Aurora kinase A by activation loop phosphorylation.

PubMed

Ruff, Emily F; Muretta, Joseph M; Thompson, Andrew R; Lake, Eric W; Cyphers, Soreen; Albanese, Steven K; Hanson, Sonya M; Behr, Julie M; Thomas, David D; Chodera, John D; Levinson, Nicholas M

2018-02-21

Many eukaryotic protein kinases are activated by phosphorylation on a specific conserved residue in the regulatory activation loop, a post-translational modification thought to stabilize the active DFG-In state of the catalytic domain. Here we use a battery of spectroscopic methods that track different catalytic elements of the kinase domain to show that the ~100 fold activation of the mitotic kinase Aurora A (AurA) by phosphorylation occurs without a population shift from the DFG-Out to the DFG-In state, and that the activation loop of the activated kinase remains highly dynamic. Instead, molecular dynamics simulations and electron paramagnetic resonance experiments show that phosphorylation triggers a switch within the DFG-In subpopulation from an autoinhibited DFG-In substate to an active DFG-In substate, leading to catalytic activation. This mechanism raises new questions about the functional role of the DFG-Out state in protein kinases. © 2018, Ruff et al.

An optimization study of PtSn/C catalysts applied to direct ethanol fuel cell: Effect of the preparation method on the electrocatalytic activity of the catalysts

NASA Astrophysics Data System (ADS)

Almeida, T. S.; Palma, L. M.; Leonello, P. H.; Morais, C.; Kokoh, K. B.; De Andrade, A. R.

2012-10-01

The aim of this work was to perform a systematic study of the parameters that can influence the composition, morphology, and catalytic activity of PtSn/C nanoparticles and compare two different methods of nanocatalyst preparation, namely microwave-assisted heating (MW) and thermal decomposition of polymeric precursors (DPP). An investigation of the effects of the reducing and stabilizing agents on the catalytic activity and morphology of Pt75Sn25/C catalysts prepared by microwave-assisted heating was undertaken for optimization purposes. The effect of short-chain alcohols such as ethanol, ethylene glycol, and propylene glycol as reducing agents was evaluated, and the use of sodium acetate and citric acid as stabilizing agents for the MW procedure was examined. Catalysts obtained from propylene glycol displayed higher catalytic activity compared with catalysts prepared in ethylene glycol. Introduction of sodium acetate enhanced the catalytic activity, but this beneficial effect was observed until a critical acetate concentration was reached. Optimization of the MW synthesis allowed for the preparation of highly dispersed catalysts with average sizes lying between 2.0 and 5.0 nm. Comparison of the best catalyst prepared by MW with a catalyst of similar composition prepared by the polymeric precursors method showed that the catalytic activity of the material can be improved when a proper condition for catalyst preparation is achieved.

Molecular ligand modulation of palladium nanocatalysts for highly efficient and robust heterogeneous oxidation of cyclohexenone to phenol

DOE PAGES

Xue, Teng; Lin, Zhaoyang; Chiu, Chin-Yi; ...

2017-01-06

Metallic nanoparticles are emerging as an exciting class of heterogeneous catalysts with the potential advantages of exceptional activity, stability, recyclability, and easier separation than homogeneous catalysts. The traditional colloid nanoparticle syntheses usually involve strong surface binding ligands that could passivate the surface active sites and result in poor catalytic activity. The subsequent removal of surface ligands could reactivate the surface but often leads to metal ion leaching and/or severe Ostwald ripening with diminished catalytic activity or poor stability. Molecular ligand engineering represents a powerful strategy for the design of homogeneous molecular catalysts but is insufficiently explored for nanoparticle catalysts tomore » date. We report a systematic investigation on molecular ligand modulation of palladium (Pd) nanoparticle catalysts. Our studies show that β-functional groups of butyric acid ligand on Pd nanoparticles can significantly modulate the catalytic reaction process to modify the catalytic activity and stability for important aerobic reactions. With a β-hydroxybutyric acid ligand, the Pd nanoparticle catalysts exhibit exceptional catalytic activity and stability with an unsaturated turnover number (TON) >3000 for dehydrogenative oxidation of cyclohexenone to phenol, greatly exceeding that of homogeneous Pd(II) catalysts (TON, ~30). This study presents a systematic investigation of molecular ligand modulation of nanoparticle catalysts and could open up a new pathway toward the design and construction of highly efficient and robust heterogeneous catalysts through molecular ligand engineering.« less

Flexibility Matters: Cooperative Active Sites in Covalent Organic Framework and Threaded Ionic Polymer.

PubMed

Sun, Qi; Aguila, Briana; Perman, Jason; Nguyen, Nicholas; Ma, Shengqian

2016-12-07

The combination of two or more reactive centers working in concert on a substrate to facilitate the reaction is now considered state of the art in catalysis, yet there still remains a tremendous challenge. Few heterogeneous systems of this sort have been exploited, as the active sites spatially separated within the rigid framework are usually difficult to cooperate. It is now shown that this roadblock can be surpassed. The underlying principle of the strategy presented here is the integration of catalytic components with excellent flexibility and porous heterogeneous catalysts, as demonstrated by the placement of linear ionic polymers in close proximity to surface Lewis acid active sites anchored on the walls of a covalent organic framework (COF). Using the cycloaddition of the epoxides and CO 2 as a model reaction, dramatic activity improvements have been achieved for the composite catalysts in relation to the individual catalytic component. Furthermore, they also clearly outperform the benchmark catalytic systems formed by the combination of the molecular organocatalysts and heterogeneous Lewis acid catalysts, while affording additional recyclability. The extraordinary flexibility and enriched concentration of the catalytically active moieties on linear polymers facilitate the concerted catalysis, thus leading to superior catalytic performance. This work therefore uncovers an entirely new strategy for designing bifunctional catalysts with double-activation behavior and opens a new avenue in the design of multicapable systems that mimic biocatalysis.

Preparation of zeolite supported TiO{sub 2}, ZnO and ZrO{sub 2} and the study on their catalytic activity in NO{sub x} reduction and 1-pentanol dehydration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fatimah, Is

Preparation of zeolite supported TiO{sub 2}, ZnO and ZrO{sub 2} and their catalytic activity was studied. Activated natural zeolite from Indonesia was utilized for the preparation and catalytic activity test on NO{sub x} reduction by NH{sub 3} 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.

In situ characterization of catalytic activity of graphene stabilized small-sized Pd nanoparticles for CO oxidation

NASA Astrophysics Data System (ADS)

Mao, Bao-Hua; Liu, Chang-Hai; Gao, Xu; Chang, Rui; Liu, Zhi; Wang, Sui-Dong

2013-10-01

The room-temperature ionic liquid assisted sputtering method is utilized to achieve the Pd-nanoparticle (NP)-graphene hybrid. The supported Pd NPs possess uniformly small sizes of 1-2 nm, which create huge surface area with ultralow Pd consumption and high NP stability. The Pd-NP-graphene hybrid is in situ characterized by the ambient pressure X-ray photoelectron spectroscopy using synchrotron radiation, and the results demonstrate high catalytic activity of the hybrid for CO oxidation. The catalytic behavior is reproducible for several catalytic cycles. The present simple and clean approach is promising to produce metal-NP-based high-efficiency catalysts for CO oxidation.

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...

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

PubMed

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

2013-05-16

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.

Composite ceria-coated aerogels and methods of making the same

DOEpatents

Eyring, Edward M; Ernst, Richard D; Turpin, Gregory C; Dunn, Brian C

2013-05-07

Ceria-coated aerogels can include an aerogel support material having a stabilized ceria coating thereon. The ceria coating can be formed by solution or vapor deposition of alcogels or aerogels. Additional catalytic metal species can also be incorporated into the coating to form multi-metallic compounds having improved catalytic activity. Further, the ceria coated aerogels retain high surface areas at elevated temperatures. Thus, improvements in catalytic activity and thermal stability can be achieved using these ceria-coated composite aerogels.

Preparation of Carbon-Platinum-Ceria and Carbon-Platinum-Cerium catalysts and its application in Polymer Electrolyte Fuel Cell: Hydrogen, Methanol, and Ethanol

NASA Astrophysics Data System (ADS)

Guzman Blas, Rolando Pedro

This thesis is focused on fuel cells using hydrogen, methanol and ethanol as fuel. Also, in the method of preparation of catalytic material for the anode: Supercritical Fluid Deposition (SFD) and impregnation method using ethylenediaminetetraacetic acid (EDTA) as a chelating agent. The first part of the thesis describes the general knowledge about Hydrogen Polymer Exchange Membrane Fuel Cell (HPEMFC),Direct Methanol Fuel Cell (DMFC) and Direct Ethanol Fuel Cell (DEFC), as well as the properties of Cerium and CeO2 (Ceria). The second part of the thesis describes the preparation of catalytic material by Supercritical Fluid Deposition (SFD). SFD was utilized to deposit Pt and ceria simultaneously onto gas diffusion layers. The Pt-ceria catalyst deposited by SFD exhibited higher methanol oxidation activity compared to the platinum catalyst alone. The linear sweep traces of the cathode made for the methanol cross over study indicate that Pt-Ceria/C as the anode catalyst, due to its better activity for methanol, improves the fuel utilization, minimizing the methanol permeation from anode to cathode compartment. The third and fourth parts of the thesis describe the preparation of material catalytic material Carbon-Platinum-Cerium by a simple and cheap impregnation method using EDTA as a chelating agent to form a complex with cerium (III). This preparation method allows the mass production of the material catalysts without additional significant cost. Fuel cell polarization and power curves experiments showed that the Carbon-Platinum-Cerium anode materials exhibited better catalytic activity than the only Vulcan-Pt catalysts for DMFC, DEFC and HPEMFC. In the case of Vulcan-20%Pt-5%w Cerium, this material exhibits better catalytic activity than the Vulcan-20%Pt in DMFC. In the case of Vulcan-40% Pt-doped Cerium, this material exhibits better catalytic activity than the Vulcan-40% Pt in DMFC, DEFC and HPEMFC. Finally, I propose a theory that explains the reason why the carbon-platinum-cerium has better catalytic activity than platinum-carbon. Due to the hybridization behavior of C and Ce could arise charge transfer, both carbon and cerium to the Platinum. Ce-C→Pt charge transfer could occur at the Ce-C/Pt interface. Thus, results in an increase in the catalytic activity of platinum-cerium-carbon when compared with carbon-platinum.

Indented Cu2MoS4 nanosheets with enhanced electrocatalytic and photocatalytic activities realized through edge engineering.

PubMed

Chen, Bang-Bao; Ma, De-Kun; Ke, Qing-Ping; Chen, Wei; Huang, Shao-Ming

2016-03-07

Edges often play a role as active centers for catalytic reactions in some nanomaterials. Therefore it is highly desirable to enhance catalytic activity of a material through modulating the microstructure of the edges. However, the study associated with edge engineering is less investigated and still at its preliminary stage. Here we report that Cu2MoS4 nanosheets with indented edges can be fabricated through a simple chemical etching route at room temperature, using Cu2MoS4 nanosheets with flat ones as sacrifice templates. Taking the electrocatalytic hydrogen evolution reaction (HER), photocatalytic degradation of rhodamine B (RhB) and conversion of benzyl alcohol as examples, the catalytic activity of Cu2MoS4 indented nanosheets (INSs) obtained through edge engineering was comparatively studied with those of Cu2MoS4 flat nanosheets (FNSs) without any modification. The photocatalytic tests revealed that the catalytic active sites of Cu2MoS4 nanosheets were associated with their edges rather than basal planes. Cu2MoS4 INSs were endowed with larger electrochemically active surface area (ECSA), more active edges and better hydrophilicity through the edge engineering. As a result, the as-fabricated Cu2MoS4 INSs exhibited an excellent HER activity with a small Tafel slope of 77 mV dec(-1), which is among the best records for Cu2MoS4 catalysts. The present work demonstrated the validity of adjusting catalytic activity of the material through edge engineering and provided a new strategy for designing and developing highly efficient catalysts.

Role of substrate dynamics in protein prenylation reactions.

PubMed

Chakravorty, Dhruva K; Merz, Kenneth M

2015-02-17

CONSPECTUS: The role dynamics plays in proteins is of intense contemporary interest. Fundamental insights into how dynamics affects reactivity and product distributions will facilitate the design of novel catalysts that can produce high quality compounds that can be employed, for example, as fuels and life saving drugs. We have used molecular dynamics (MD) methods and combined quantum mechanical/molecular mechanical (QM/MM) methods to study a series of proteins either whose substrates are too far away from the catalytic center or whose experimentally resolved substrate binding modes cannot explain the observed product distribution. In particular, we describe studies of farnesyl transferase (FTase) where the farnesyl pyrophosphate (FPP) substrate is ∼8 Å from the zinc-bound peptide in the active site of FTase. Using MD and QM/MM studies, we explain how the FPP substrate spans the gulf between it and the active site, and we have elucidated the nature of the transition state (TS) and offered an alternate explanation of experimentally observed kinetic isotope effects (KIEs). Our second story focuses on the nature of substrate dynamics in the aromatic prenyltransferase (APTase) protein NphB and how substrate dynamics affects the observed product distribution. Through the examples chosen we show the power of MD and QM/MM methods to provide unique insights into how protein substrate dynamics affects catalytic efficiency. We also illustrate how complex these reactions are and highlight the challenges faced when attempting to design de novo catalysts. While the methods used in our previous studies provided useful insights, several clear challenges still remain. In particular, we have utilized a semiempirical QM model (self-consistent charge density functional tight binding, SCC-DFTB) in our QM/MM studies since the problems we were addressing required extensive sampling. For the problems illustrated, this approach performed admirably (we estimate for these systems an uncertainty of ∼2 kcal/mol), but it is still a semiempirical model, and studies of this type would benefit greatly from more accurate ab initio or DFT models. However, the challenge with these methods is to reach the level of sampling needed to study systems where large conformational changes happen in the many nanoseconds to microsecond time regimes. Hence, how to couple expensive and accurate QM methods with sophisticated sampling algorithms is an important future challenge especially when large-scale studies of catalyst design become of interest. The use of MD and QM/MM models to elucidate enzyme catalytic pathways and to design novel catalytic agents is in its infancy but shows tremendous promise. While this Account summarizes where we have been, we also discuss briefly future directions that improve our fundamental ability to understand enzyme catalysis.

The doping effect on the catalytic activity of graphene for oxygen evolution reaction in a lithium-air battery: a first-principles study.

PubMed

Ren, Xiaodong; Wang, Beizhou; Zhu, Jinzhen; Liu, Jianjun; Zhang, Wenqing; Wen, Zhaoyin

2015-06-14

A lithium-air battery as an energy storage technology can be used in electric vehicles due to its large energy density. However, its poor rate capability, low power density and large overpotential problems limit its practical usage. In this paper, the first-principles thermodynamic calculations were performed to study the catalytic activity of X-doped graphene (X = B, N, Al, Si, and P) materials as potential cathodes to enhance charge reactions in a lithium-air battery. Among these materials, P-doped graphene exhibits the highest catalytic activity in reducing the charge voltage by 0.25 V, while B-doped graphene has the highest catalytic activity in decreasing the oxygen evolution barrier by 0.12 eV. By combining these two catalytic effects, B,P-codoped graphene was demonstrated to have an enhanced catalytic activity in reducing the O2 evolution barrier by 0.70 eV and the charge voltage by 0.13 V. B-doped graphene interacts with Li2O2 by Li-sited adsorption in which the electron-withdrawing center can enhance charge transfer from Li2O2 to the substrate, facilitating reduction of O2 evolution barrier. In contrast, X-doped graphene (X = N, Al, Si, and P) prefers O-sited adsorption toward Li2O2, forming a X-O2(2-)···Li(+) interface structure between X-O2(2-) and the rich Li(+) layer. The active structure of X-O2(2-) can weaken the surrounding Li-O2 bonds and significantly reduce Li(+) desorption energy at the interface. Our investigation is helpful in developing a novel catalyst to enhance oxygen evolution reaction (OER) in Li-air batteries.

Function of specific 2'-hydroxyl groups of guanosines in a hammerhead ribozyme probed by 2' modifications.

PubMed Central

Williams, D M; Pieken, W A; Eckstein, F

1992-01-01

The importance of the 2'-hydroxyl group of several guanosine residues for the catalytic efficiency of a hammerhead ribozyme has been investigated. Five ribozymes in which single guanosine residues were substituted with 2'-amino-, 2'-fluoro-, or 2'-deoxyguanosine were chemically synthesized. The comparison of the catalytic activity of the three 2' modifications at a specific position allows conclusions about the functional role of the parent 2'-hydroxyl group. Substitutions of nonconserved nucleotides within the ribozyme caused little alteration in the catalytic activity relative to that obtained with the unmodified ribozyme. In contrast, when either of the guanosines within the single-stranded loop between stem I and stem II of the ribozyme was replaced by 2'-deoxyguanosine or 2'-fluoro-2'-deoxyguanosine, the catalytic activities of the resulting ribozymes were reduced by factors of at least 150. The catalytic activities of the corresponding ribozymes containing 2'-amino-2'-deoxyguanosine substitutions at these positions, however, were both reduced by factors of 15. These effects resulted from decreases in the respective kcat values, whereas variations in the Km values were comparatively small. A different pattern of reactivity of the three 2' modifications was observed at the guanosine immediately 3' to stem II of the ribozyme. Whereas both 2'-deoxyguanosine and 2'-amino-2'-deoxyguanosine at this position showed catalytic activity similar to that of the unmodified ribozyme, the activity of the corresponding 2'-fluoro-2'-deoxyguanosine-containing ribozyme was reduced by a factor of 15. The implications of these substitution-specific reactivities on the functional role of the native 2'-hydroxyl groups are discussed. Images PMID:1736306

The Metabolic Core and Catalytic Switches Are Fundamental Elements in the Self-Regulation of the Systemic Metabolic Structure of Cells

PubMed Central

De la Fuente, Ildefonso M.; Cortes, Jesus M.; Perez-Pinilla, Martin B.; Ruiz-Rodriguez, Vicente; Veguillas, Juan

2011-01-01

Background Experimental observations and numerical studies with dissipative metabolic networks have shown that cellular enzymatic activity self-organizes spontaneously leading to the emergence of a metabolic core formed by a set of enzymatic reactions which are always active under all environmental conditions, while the rest of catalytic processes are only intermittently active. The reactions of the metabolic core are essential for biomass formation and to assure optimal metabolic performance. The on-off catalytic reactions and the metabolic core are essential elements of a Systemic Metabolic Structure which seems to be a key feature common to all cellular organisms. Methodology/Principal Findings In order to investigate the functional importance of the metabolic core we have studied different catalytic patterns of a dissipative metabolic network under different external conditions. The emerging biochemical data have been analysed using information-based dynamic tools, such as Pearson's correlation and Transfer Entropy (which measures effective functionality). Our results show that a functional structure of effective connectivity emerges which is dynamical and characterized by significant variations of bio-molecular information flows. Conclusions/Significance We have quantified essential aspects of the metabolic core functionality. The always active enzymatic reactions form a hub –with a high degree of effective connectivity- exhibiting a wide range of functional information values being able to act either as a source or as a sink of bio-molecular causal interactions. Likewise, we have found that the metabolic core is an essential part of an emergent functional structure characterized by catalytic modules and metabolic switches which allow critical transitions in enzymatic activity. Both, the metabolic core and the catalytic switches in which also intermittently-active enzymes are involved seem to be fundamental elements in the self-regulation of the Systemic Metabolic Structure. PMID:22125607

A Monoclonal Antibody to Cryptococcus neoformans Glucuronoxylomannan Manifests Hydrolytic Activity for Both Peptides and Polysaccharides.

PubMed

Bowen, Anthony; Wear, Maggie P; Cordero, Radames J B; Oscarson, Stefan; Casadevall, Arturo

2017-01-13

Studies in the 1980s first showed that some natural antibodies were "catalytic" and able to hydrolyze peptide or phosphodiester bonds in antigens. Many naturally occurring catalytic antibodies have since been isolated from human sera and associated with positive and negative outcomes in autoimmune disease and infection. The function and prevalence of these antibodies, however, remain unclear. A previous study suggested that the 18B7 monoclonal antibody against glucuronoxylomannan (GXM), the major component of the Cryptococcus neoformans polysaccharide capsule, hydrolyzed a peptide antigen mimetic. Using mass spectrometry and Förster resonance energy transfer techniques, we confirm and characterize the hydrolytic activity of 18B7 against peptide mimetics and show that 18B7 is able to hydrolyze an oligosaccharide substrate, providing the first example of a naturally occurring catalytic antibody for polysaccharides. Additionally, we show that the catalytic 18B7 antibody increases release of capsular polysaccharide from fungal cells. A serine protease inhibitor blocked peptide and oligosaccharide hydrolysis by 18B7, and a putative serine protease-like active site was identified in the light chain variable region of the antibody. An algorithm was developed to detect similar sites present in unique antibody structures in the Protein Data Bank. The putative site was found in 14 of 63 (22.2%) catalytic antibody structures and 119 of 1602 (7.4%) antibodies with no annotation of catalytic activity. The ability of many antibodies to cleave antigen, albeit slowly, supports the notion that this activity is an important immunoglobulin function in host defense. The discovery of GXM hydrolytic activity suggests new therapeutic possibilities for polysaccharide-binding antibodies. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc.

Preparation of immobilized coating Fenton-like catalyst for high efficient degradation of phenol.

PubMed

Wang, Jiankang; Yao, Zhongping; Wang, Yajing; Xia, Qixing; Chu, Huiya; Jiang, Zhaohua

2017-05-01

In this study, solid acid amorphous Fe 3 O 4 /SiO 2 ceramic coating decorated with sulfur on Q235 carbon steel as Fenton-like catalyst for phenol degradation was successfully prepared by plasma electrolytic oxidation (PEO) in silicate electrolyte containing Na 2 S 2 O 8 as sulfur source. The surface morphology and phase composition were characterized by SEM, EDS, XRD and XPS analyses. NH 3 -TPD was used to evaluate surface acidity of PEO coating. The results indicated that sulfur decorated amorphous Fe 3 O 4 /SiO 2 ceramic coatings with porous structure and higher acid strength had the similar pore size and the surface became more and more uneven with the increase of Na 2 S 2 O 8 in the silicate electrolyte. The Fenton-like catalytic activity of sulfur decorated PEO coatings was also evaluated. In contrast to negligible catalytic activity of sulfur undecorated PEO coating, catalytic activity of sulfur decorated PEO coating was excellent and PEO coating prepared with 3.0 g Na 2 S 2 O 8 had the highest catalytic activity which could degrade 99% of phenol within 8 min under circumneutral pH. The outstanding performance of sulfur decorated PEO coating was attributed to strong acidic microenvironment and more Fe 2+ on the surface. The strong acid sites played a key factor in determining catalytic activity of catalyst. In conclusion, rapid phenol removal under circumneutral pH and easier separation endowed it potential application in wastewater treatment. In addition, this strategy of preparing immobilized solid acid coating could provide guidance for designing Fenton-like catalyst with excellent catalytic activity and easier separation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Influence of active site location on catalytic activity in de novo-designed zinc metalloenzymes.

PubMed

Zastrow, Melissa L; Pecoraro, Vincent L

2013-04-17

While metalloprotein design has now yielded a number of successful metal-bound and even catalytically active constructs, the question of where to put a metal site along a linear, repetitive sequence has not been thoroughly addressed. Often several possibilities in a given sequence may exist that would appear equivalent but may in fact differ for metal affinity, substrate access, or protein dynamics. We present a systematic variation of active site location for a hydrolytically active ZnHis3O site contained within a de novo-designed three-stranded coiled coil. We find that the maximal rate, substrate access, and metal-binding affinity are dependent on the selected position, while catalytic efficiency for p-nitrophenyl acetate hydrolysis can be retained regardless of the location of the active site. This achievement demonstrates how efficient, tailor-made enzymes which control rate, pKa, substrate and solvent access (and selectivity), and metal-binding affinity may be realized. These findings may be applied to the more advanced de novo design of constructs containing secondary interactions, such as hydrogen-bonding channels. We are now confident that changes to location for accommodating such channels can be achieved without location-dependent loss of catalytic efficiency. These findings bring us closer to our ultimate goal of incorporating the secondary interactions we believe will be necessary in order to improve both active site properties and the catalytic efficiency to be competitive with the native enzyme, carbonic anhydrase.

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 RuO x/TiO 2(110) catalysts have a remarkable catalytic activity for CO oxidation at temperatures in the range of 350–375 K. Furthermore, the RuO 2(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 RuO 2(110) to 0.66 eV in RuO x/TiO 2(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 COmore » and O species to give CO 2 (the main barrier for the CO oxidation reaction) passing from around 0.7 eV in RuO 2(110) to 0.55 eV in RuO x/TiO 2(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

The DNLZ/HEP zinc-binding subdomain is critical for regulation of the mitochondrial chaperone HSPA9

PubMed Central

Vu, Michael T; Zhai, Peng; Lee, Juhye; Guerra, Cecilia; Liu, Shirley; Gustin, Michael C; Silberg, Jonathan J

2012-01-01

Human mitochondrial DNLZ/HEP regulates the catalytic activity and solubility of the mitochondrial hsp70 chaperone HSPA9. Here, we investigate the role that the DNLZ zinc-binding and C-terminal subdomains play in regulating HSPA9. We show that truncations lacking portions of the zinc-binding subdomain (ZBS) do not affect the solubility of HSPA9 or its ATPase domain, whereas those containing the ZBS and at least 10 residues following this subdomain enhance chaperone solubility. Binding measurements further show that DNLZ requires its ZBS to form a stable complex with the HSPA9 ATPase domain, and ATP hydrolysis measurements reveal that the ZBS is critical for full stimulation of HSPA9 catalytic activity. We also examined if DNLZ is active in vivo. We found that DNLZ partially complements the growth of Δzim17Saccharomyces cerevisiae, and we discovered that a Zim17 truncation lacking a majority of the C-terminal subdomain strongly complements growth like full-length Zim17. These findings provide direct evidence that human DNLZ is a functional ortholog of Zim17. In addition, they implicate the pair of antiparallel β-strands that coordinate zinc in Zim17/DNLZ-type proteins as critical for binding and regulating hsp70 chaperones. PMID:22162012

The DNLZ/HEP zinc-binding subdomain is critical for regulation of the mitochondrial chaperone HSPA9.

PubMed

Vu, Michael T; Zhai, Peng; Lee, Juhye; Guerra, Cecilia; Liu, Shirley; Gustin, Michael C; Silberg, Jonathan J

2012-02-01

Human mitochondrial DNLZ/HEP regulates the catalytic activity and solubility of the mitochondrial hsp70 chaperone HSPA9. Here, we investigate the role that the DNLZ zinc-binding and C-terminal subdomains play in regulating HSPA9. We show that truncations lacking portions of the zinc-binding subdomain (ZBS) do not affect the solubility of HSPA9 or its ATPase domain, whereas those containing the ZBS and at least 10 residues following this subdomain enhance chaperone solubility. Binding measurements further show that DNLZ requires its ZBS to form a stable complex with the HSPA9 ATPase domain, and ATP hydrolysis measurements reveal that the ZBS is critical for full stimulation of HSPA9 catalytic activity. We also examined if DNLZ is active in vivo. We found that DNLZ partially complements the growth of Δzim17 Saccharomyces cerevisiae, and we discovered that a Zim17 truncation lacking a majority of the C-terminal subdomain strongly complements growth like full-length Zim17. These findings provide direct evidence that human DNLZ is a functional ortholog of Zim17. In addition, they implicate the pair of antiparallel β-strands that coordinate zinc in Zim17/DNLZ-type proteins as critical for binding and regulating hsp70 chaperones. Copyright © 2011 The Protein Society.

Cobalt nanoparticles encapsulated in nitrogen-rich carbon nanotubes as efficient catalysts for organic pollutants degradation via sulfite activation.

PubMed

Wu, Deming; Ye, Peng; Wang, Manye; Wei, Yi; Li, Xiaoxia; Xu, Aihua

2018-06-15

The activation of sulfite by heterogeneous catalysts displays a great potential in the development of new sulfate radials based technologies for wastewater treatment. Herein, cobalt nanoparticles embedded in N-doped carbon nanotubes (Co@NC) were prepared by a simple pyrolysis method. Due to the synergistic effects of the cobalt nanoparticles and N-doped carbon nanotubes, the Co@NC catalyst intrinsically shows an outstanding efficiency, excellent reusability and high stability in the catalytic oxidation of methyl orange (MO) in the presence of sulfite and dioxygen. The structure and efficiency of the catalyst was significantly affected by the content of cobalt and pyrolysis temperature. Several quenching experiments and electron paramagnetic resonance were carried out to investigate the catalytic mechanism. It is found that hydroxyl and sulfate radicals worked together to degrade MO in the system. The formation and decomposition of peroxymonosulfate may be an important route of these reactive radicals production. The effect of different anions, bicarbonate concentration, initial solution pH and dye types on the performance of the catalyst was also studied. This study can open a new approach for design and preparation of encapsulated cobalt in carbon materials as effective catalysts for pollutants degradation via sulfite activation. Copyright © 2018 Elsevier B.V. All rights reserved.

Calmodulin fishing with a structurally disordered bait triggers CyaA catalysis

PubMed Central

O’Brien, Darragh P.; Durand, Dominique; Voegele, Alexis; Hourdel, Véronique; Davi, Marilyne; Chamot-Rooke, Julia; Vachette, Patrice; Brier, Sébastien; Ladant, Daniel

2017-01-01

Once translocated into the cytosol of target cells, the catalytic domain (AC) of the adenylate cyclase toxin (CyaA), a major virulence factor of Bordetella pertussis, is potently activated by binding calmodulin (CaM) to produce supraphysiological levels of cAMP, inducing cell death. Using a combination of small-angle X-ray scattering (SAXS), hydrogen/deuterium exchange mass spectrometry (HDX-MS), and synchrotron radiation circular dichroism (SR-CD), we show that, in the absence of CaM, AC exhibits significant structural disorder, and a 75-residue-long stretch within AC undergoes a disorder-to-order transition upon CaM binding. Beyond this local folding, CaM binding induces long-range allosteric effects that stabilize the distant catalytic site, whilst preserving catalytic loop flexibility. We propose that the high enzymatic activity of AC is due to a tight balance between the CaM-induced decrease of structural flexibility around the catalytic site and the preservation of catalytic loop flexibility, allowing for fast substrate binding and product release. The CaM-induced dampening of AC conformational disorder is likely relevant to other CaM-activated enzymes. PMID:29287065

Polyelectrolyte induced formation of silver nanoparticles in copolymer hydrogel and their application as catalyst

DOE Office of Scientific and Technical Information (OSTI.GOV)

He, Yongqiang; Huang, Guanbo, E-mail: gbhuang2007@hotmail.com; Pan, Zeng

2015-10-15

Highlights: • A simple route for the in situ preparation of Ag nanoparticles has been developed. • The Ag loaded hydrogel showed catalytic activity for reduction of 4-nitrophenol. • The catalyst can be recovered by simple separation and showed good recyclability. - Abstract: A simple route for the in situ preparation of catalytically active Ag nanoparticles (NPs) in hydrogel networks has been developed. The electronegativity of the amide and carboxyl groups on the poly(acrylamide-co-acryl acid) chains caused strong binding of the Ag{sup +} ions which made the ions distribute uniformly inside the hydrogels. When the Ag{sup +} loaded hydrogels weremore » immersed in NaBH{sub 4} solution, the Ag{sup +} ions on the polymer networks were reduced to Ag NPs. The resultant hydrogel showed good catalytic activity for the reduction of a common organic pollutant, 4-nitrophenol, with sodium borohydride. A kinetic study of the catalytic reaction was carried out and a possible reason for the decline of the catalytic performance with reuse is proposed.« less

Facile synthesis of polypyrrole functionalized nickel foam with catalytic activity comparable to Pt for the poly-generation of hydrogen and electricity

NASA Astrophysics Data System (ADS)

Tang, Tiantian; Li, Kan; Shen, Zhemin; Sun, Tonghua; Wang, Yalin; Jia, Jinping

2016-01-01

Polypyrrole functionalized nickel foam is facilely prepared through the potentiostatic electrodeposition. The PPy-functionalized Ni foam functions as a hydrogen-evolution cathode in a rotating disk photocatalytic fuel cell, in which hydrogen energy and electric power are generated by consuming organic wastes. The PPy-functionalized Ni foam cathode exhibits stable catalytic activities after thirteen continuous runs. Compared with net or plate structure, the Ni foam with a unique three-dimensional reticulate structure is conducive to the electrodeposition of PPy. Compared with Pt-group electrode, PPy-coated Ni foam shows a satisfactory catalytic performance for the H2 evolution. The combination of PPy and Ni forms a synergistic effect for the rapid trapping and removal of proton from solution and the catalytic reduction of proton to hydrogen. The PPy-functionalized Ni foam could be applied in photocatalytic and photoelectrochemical generation of H2. In all, we report a low cost, high efficient and earth abundant PPy-functionalized Ni foam with a satisfactory catalytic activities comparable to Pt for the practical application of poly-generation of hydrogen and electricity.

Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

PubMed

Krutpijit, Chadaporn; Jongsomjit, Bunjerd

2016-01-01

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

Heterogeneous catalytic ozonation of dibutyl phthalate in aqueous solution in the presence of iron-loaded activated carbon.

PubMed

Huang, Yuanxing; Cui, Chenchen; Zhang, Daofang; Li, Liang; Pan, Ding

2015-01-01

Iron-loaded activated carbon was prepared and used as catalyst in heterogeneous catalytic ozonation of dibutyl phthalate (DBP). The catalytic activity of iron-loaded activated carbon was investigated under various conditions and the mechanisms of DBP removal were deduced. Characterization of catalyst indicated that the iron loaded on activated carbon was mainly in the form of goethite, which reduced its surface area, pore volume and pore diameter. The presence of metals on activated carbon positively contributed to its catalytic activity in ozonation of DBP. Iron loading content of 15% and initial water pH of 8 achieved highest DBP removal among all the tried conditions. Catalyst dosage of 10 mg L(-1) led to approximately 25% of increase in DBP (initial concentration 2 mg L(-1)) removal in 60 min as compared with ozone alone, and when catalyst dosage increased to 100 mg L(-1), the DBP removal was further improved by 46%. Based on a comparison of reaction rates for direct and indirect transformation of DBP, the increased removal of DBP in this study likely occurred via transformation of ozone into hydroxyl radicals on the catalyst surface. Copyright © 2014 Elsevier Ltd. All rights reserved.

New Method To Generate Enzymatically Deficient Clostridium difficile Toxin B as an Antigen for Immunization

PubMed Central

Genth, Harald; Selzer, Jörg; Busch, Christian; Dumbach, Jürgen; Hofmann, Fred; Aktories, Klaus; Just, Ingo

2000-01-01

The family of the large clostridial cytotoxins, encompassing Clostridium difficile toxins A and B as well as the lethal and hemorrhagic toxins from Clostridium sordellii, monoglucosylate the Rho GTPases by transferring a glucose moiety from the cosubstrate UDP-glucose. Here we present a new detoxification procedure to block the enzyme activity by treatment with the reactive UDP-2′,3′-dialdehyde to result in alkylation of toxin A and B. Alkylation is likely to occur in the catalytic domain, because the native cosubstrate UDP-glucose completely protected the toxins from inactivation and the alkylated toxin competes with the native toxin at the cell receptor. Alkylated toxins are good antigens resulting in antibodies recognizing only the C-terminally located receptor binding domain, whereas formaldehyde treatment resulted in antibodies recognizing both the receptor binding domain and the catalytic domain, indicating that the catalytic domain is concealed under native conditions. Antibodies against the native catalytic domain (amino acids 1 through 546) and those holotoxin antibodies recognizing the catalytic domain inhibited enzyme activity. However, only antibodies against the receptor binding domain protected intact cells from the cytotoxic activity of toxin B, whereas antibodies against the catalytic domain were protective only when inside the cell. PMID:10678912

Substrate-specifying determinants of the nucleotide pyrophosphatases/phosphodiesterases NPP1 and NPP2

PubMed Central

2004-01-01

The nucleotide pyrophosphatases/phosphodiesterases NPP1 and NPP2/autotaxin are structurally related eukaryotic ecto-enzymes, but display a very different substrate specificity. NPP1 releases nucleoside 5′-monophosphates from various nucleotides, whereas NPP2 mainly functions as a lysophospholipase D. We have used a domain-swapping approach to map substrate-specifying determinants of NPP1 and NPP2. The catalytic domain of NPP1 fused to the N- and C-terminal domains of NPP2 was hyperactive as a nucleotide phosphodiesterase, but did not show any lysophospholipase D activity. In contrast, chimaeras of the catalytic domain of NPP2 and the N- and/or C-terminal domains of NPP1 were completely inactive. These data indicate that the catalytic domain as well as both extremities of NPP2 contain lysophospholipid-specifying sequences. Within the catalytic domain of NPP1 and NPP2, we have mapped residues close to the catalytic site that determine the activities towards nucleotides and lysophospholipids. We also show that the conserved Gly/Phe-Xaa-Gly-Xaa-Xaa-Gly (G/FXGXXG) motif near the catalytic site is required for metal binding, but is not involved in substrate-specification. Our data suggest that the distinct activities of NPP1 and NPP2 stem from multiple differences throughout the polypeptide chain. PMID:15096095

Amine-functionalized Zn(ii) MOF as an efficient multifunctional catalyst for CO2 utilization and sulfoxidation reaction.

PubMed

Patel, Parth; Parmar, Bhavesh; Kureshy, Rukhsana I; Khan, Noor-Ul H; Suresh, Eringathodi

2018-06-19

Herein, a zinc(ii)-based 3D mixed ligand metal organic framework (MOF) was synthesized via versatile routes including green mechanochemical synthesis. The MOF {[Zn(ATA)(L)·H2O]}n (ZnMOF-1-NH2) has been characterized by various physico-chemical techniques, including SCXRD, and composed of the bipyridyl-based Schiff base (E)-N'-(pyridin-4-ylmethylene)isonicotinohydrazide (L) and 2-aminoterephthalic acid (H2ATA) ligands as linkers. The MOF material has been explored as a multifunctional heterogeneous catalyst for the cycloaddition of alkyl and aryl epoxides with CO2 and sulfoxidation reactions of aryl sulfides. The influence of various reaction parameters is examined to optimize the performance of the catalytic reactions. It is found that solvent-free catalytic reaction conditions offer good catalytic conversion in the case of cyclic carbonates, and for sulfoxide, good conversion and selectivity are achieved in the presence of DCM as a solvent medium under ambient reaction conditions. The chemical and thermal stability of the catalyst are excellent and it is active for up to four catalytic cycles without significant loss in activity. Furthermore, based on the catalytic activity and structural evidence, a plausible mechanism for both catalytic reactions is proposed.

Silver nanocrystal-decorated polyoxometalate single-walled nanotubes as nanoreactors for desulfurization catalysis at room temperature.

PubMed

Zhang, Hao; Xu, Xiaobin; Lin, Haifeng; Ud Din, Muhammad Aizaz; Wang, Haiqing; Wang, Xun

2017-09-14

Ultrathin nanocrystals generally provide a remarkable catalytic performance due to their high specific surface area and exposure of certain active sites. However, deactivation caused by growth and gathering limits the catalytic application of ultrathin nanocrystals. Here we report Ag nanocrystal-decorated polyoxometalate (Ag-POM) single-walled nanotubes assembled via a concise, surfactant-free soaking method as a new kind of well-defined core-sheath nanoreactor. The diameter of Ag nanocrystals inside polyoxometalate nanotubes can be controlled via simply adjusting the reactant concentration. Ag-POM provided outstanding oxidative desulfurization (ODS) catalytic performance for aromatic sulfocompounds at room temperature. It was suggested that Ag nanocrystals decorated on the inner surface played a key role in adjusting the electronic distribution and enhancing the catalytic activity. The as-prepared Ag-POM nanotubes are promising candidate catalysts with enhanced performance for practical catalytic applications in the gasoline desulfurization industry.

Engineering New Catalysts for In-Process Elimination of Tars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Felix, Larry G.

2012-09-30

The key objective of this project was to develop a new and more efficient methodology for engineering and economically producing optimized robust catalysts for the reduction or elimination of tars in biomass gasification. Whereas current catalyst technology typically disposes thin layers of catalytically-active material onto rigid supports via wet chemistry-based methods, this project investigated novel thermal methods for directly incorporating catalytically active materials onto robust supports as well as novel approaches for incorporating catalytically active materials on and/or within an otherwise inert refractory support material which is then subsequently formed and processed to create a catalytically-active material on all exposedmore » surfaces. Specifically, the focus of this engineered catalyst development was on materials which were derived from, or otherwise related to, olivine-like minerals, due to the inherent attrition resistance and moderate catalytic properties exhibited by natural olivine when used in a fluidized bed biomass gasifier. Task 1 of this project successfully demonstrated the direct thermal impregnation of catalytically-active materials onto an olivine substrate, with the production of a Ni-olivine catalyst. Nickel and nickel oxide were thermally impregnated onto an olivine substrate and when reduced were shown to demonstrate improved catalytic activity over the baseline olivine material and equal the tar-decomposing performance of Ni-olivine catalysts prepared by conventional wet impregnation. Task 2 involved coordination with our subcontracted project partners to further develop and characterize catalyst formulations and to optimize activity and production methods. Within this task, several significant new materials were developed. NexTech Materials developed a sintered ceramic nickel-magnesium-silicate catalyst that demonstrated superb catalytic activity and high resistance to deactivation by H2S. Alfred University developed both supported and integrated (bulk) catalysts via a glass-ceramic processing route which were shown to exhibit excellent catalytic activity and superior resistance to attrition deactivation. With the discovery of these active, robust, glass-based catalysts, and with the permission of the project officer, the investigation of waste-based materials as originally proposed for Task 3 and pilot-scale testing proposed in Task 5 were deferred indefinitely in favor of further investigation of the glass-ceramic based catalyst materials. This choice was justified in part because during FY 2006 and through FY 2007, funding restrictions imposed by congressional budget choices significantly reduced funding for DOE biomass-related projects. Funding for this project was limited to what had been authorized which slowed the pace of project work at GTI so that our project partners could continue in their work. Thereafter, project work was allowed to resume and with restored funding, the project continued and concentrated on the development and testing of glass-ceramic catalysts in bulk or supported formats. Work concluded with a final development devoted to increasing the surface area of glass-ceramic catalysts in the form of microspheres. Following that development, project reporting was completed and the project was concluded.« less

Nanofibrous electrocatalysts

DOEpatents

Liu, Di Jia; Shui, Jianglan; Chen, Chen

2016-05-24

A nanofibrous catalyst and method of manufacture. A precursor solution of a transition metal based material is formed into a plurality of interconnected nanofibers by electro-spinning the precursor solution with the nanofibers converted to a catalytically active material by a heat treatment. Selected subsequent treatments can enhance catalytic activity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gianetto, A.; Farag, H.I.; Blasetti, A.P.

Changes of the relative importance of intradiffusion on USY zeolite crystals were studied as a way of affecting selectivity of catalytic cracking reactions. Zeolite crystals were synthesized (Si/Al = 2.4), activated and stabilized using ion exchange and steam calcination to obtain USSY (Ultra Stable Submicron Y) zeolites. After the activation the zeolites were pelletized (45--60 [mu]m particles). USSYs were tested in a novel Riser Simulator. Results obtained show that total aromatics (BTX), benzene, C[sub 4] olefins, and coke were significantly affected with the change of zeolite crystal sizes. Gasolines produced with USSY zeolites contain less aromatics and particularly lower benzenemore » levels. Experimental results were analyzed with a model including several lumps: unconverted gas oil, gasoline, light gases, and coke. This model also accounts for catalyst deactivation as a function of coke on catalyst. Various kinetic parameters were determined with their corresponding spans for the 95% level of confidence.« less

Dual Active Site in the Endolytic Transglycosylase gp144 of Bacteriophage phiKZ.

PubMed

Chertkov, O V; Armeev, G A; Uporov, I V; Legotsky, S A; Sykilinda, N N; Shaytan, A K; Klyachko, N L; Miroshnikov, K A

2017-01-01

Lytic transglycosylases are abundant peptidoglycan lysing enzymes that degrade the heteropolymers of bacterial cell walls in metabolic processes or in the course of a bacteriophage infection. The conventional catalytic mechanism of transglycosylases involves only the Glu or Asp residue. Endolysin gp144 of Pseudomonas aeruginosa bacteriophage phiKZ belongs to the family of Gram-negative transglycosylases with a modular composition and C -terminal location of the catalytic domain. Glu115 of gp144 performs the predicted role of a catalytic residue. However, replacement of this residue does not completely eliminate the activity of the mutant protein. Site-directed mutagenesis has revealed the participation of Tyr197 in the catalytic mechanism, as well as the presence of a second active site involving Glu178 and Tyr147. The existence of the dual active site was supported by computer modeling and monitoring of the molecular dynamics of the changes in the conformation and surface charge distribution as a consequence of point mutations.

Rhenium doping induced structural transformation in mono-layered MoS2 with improved catalytic activity for hydrogen evolution reaction

NASA Astrophysics Data System (ADS)

Shi, Wenwu; Wang, Zhiguo; Qing Fu, Yong

2017-10-01

This paper reports a new design methodology to improve catalytic activities of catalysts based on 2D transition metal dichalcogenides through elemental doping which induces structural transformations. Effects of rhenium (Re) doping on structural stability/phase transformation and catalytic activity of mono-layered trigonal prismatic (2H) MoS2 were investigated using density functional theory as one example. Results show that 2H-Mo1-x Re x S2 transforms into 1T‧-Mo1-x Re x S2MoS2 as the value of x is larger than 0.4, and the transfer of the electron from Re to Mo is identified as the main reason for this structural transformation. The 1T‧-Mo1-x Re x S2 shows a good catalytic activity for the hydrogen evolution reaction when 0.75  ⩽  x  ⩽  0.94.

Supercritical CO{sub 2} mediated synthesis and catalytic activity of graphene/Pd nanocomposites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Lulu; Nguyen, Van Hoa; Department of Chemistry, Nha Trang University, 2 Nguyen Dinh Chieu, Nha Trang

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 electronmore » 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.« less

Catalytic conversion of methane to methanol using Cu-zeolites.

PubMed

Alayon, Evalyn Mae C; Nachtegaal, Maarten; Ranocchiari, Marco; van Bokhoven, Jeroen A

2012-01-01

The conversion of methane to value-added liquid chemicals is a promising answer to the imminent demand for fuels and chemical synthesis materials in the advent of a dwindling petroleum supply. Current technology requires high energy input for the synthesis gas production, and is characterized by low overall selectivity, which calls for alternative reaction routes. The limitation to achieve high selectivity is the high C-H bond strength of methane. High-temperature reaction systems favor gas-phase radical reactions and total oxidation. This suggests that the catalysts for methane activation should be active at low temperatures. The enzymatic-inspired metal-exchanged zeolite systems apparently fulfill this need, however, methanol yield is low and a catalytic process cannot yet be established. Homogeneous and heterogeneous catalytic systems have been described which stabilize the intermediate formed after the first C-H activation. The understanding of the reaction mechanism and the determination of the active metal sites are important for formulating strategies for the upgrade of methane conversion catalytic technologies.

Direct evidence that FK506 inhibition of FcepsilonRI-mediated exocytosis from RBL mast cells involves calcineurin.

PubMed

Hultsch, T; Brand, P; Lohmann, S; Saloga, J; Kincaid, R L; Knop, J

1998-05-01

FcepsilonRI-mediated exocytosis of preformed mediators from mast cells and basophils (e.g. histamine, serotonin, beta-hexosaminidase) is sensitive to the immunosuppressants cyclosporin A and FK506 (IC50 200 and 4 nM, respectively) but not rapamycin. The mechanism of inhibition does not appear to involve tyrosine phosphorylation, hydrolysis of inositol phosphates or calcium flux. Here we report experiments using a molecular approach to assess the role of calcineurin, a serine/threonine phosphatase thought to be the primary pharmacological target of these drugs. Calcineurin's activity requires association of its catalytic (A) subunit with an intrinsic regulatory (B) subunit. We hypothesized that calcineurin-sensitive signalling events should be affected by the depletion of calcineurin B subunits, thereby reducing the number of active A:B complexes. We therefore transfected rat basophilic leukemia (RBL) cells with an inhibitory (dominant negative) form of the calcineurin A subunit, which binds the calcineurin B subunit with high affinity but does not possess catalytic activity (B subunit knock-out, BKO). In these transfected cells, the dose-response curve for the inhibition of FcepsilonRI-mediated exocytosis by FK506 was shifted to the left, indicating an increased drug sensitivity of BKO-transfected cells. We conclude that FK506 inhibition of FcepsilonRI-mediated exocytosis in mast cells specifically targets calcineurin activity.

[State of Fungal Lipases of Rhizopus microsporus, Penicillium sp. and Oospora lactis in Border Layers Water-Solid Phase and Factors Affecting Catalytic Properties of Enzymes].

PubMed

Khasanov, Kh T; Davranov, K; Rakhimov, M M

2015-01-01

We demonstrated that a change in the catalytic activity of fungal lipases synthesized by Rhizopus microsporus, Penicillium sp. and Oospora lactis and their ability to absorb on different sorbents depended on the nature of groups on the solid phase surface in the model systems water: lipid and water: solid phase. Thus, the stability of Penicillium sp. lipases increased 85% in the presence ofsorsilen or DEAE-cellulose, and 55% of their initial activity respectively was preserved. In the presence of silica gel and CM-cellulose, a decreased rate of lipid hydrolysis by Pseudomonas sp. enzymes was observed in water medium, and the hydrolysis rate increased by 2.4 and 1.5 times respectively in the presence of aminoaerosil and polykefamid. In an aqueous-alcohol medium, aminoaerosil and polykefamid decreased the rate of substrate hydrolysis by more than 30 times. The addition of aerosil to aqueous and aqueous-alcohol media resulted in an increase in the hydrolysis rate by 1.2-1.3 times. Sorsilen stabilized Penicillium sp. lipase activity at 40, 45, 50 and 55 degrees C. Either stabilization or inactivation of lipases was observed depending on the pH of the medium and the nature of chemical groups localized on the surface of solid phase. The synthetizing activity of lipases also changed depending on the conditions.

A Distal Disulfide Bridge in OXA-1 β-Lactamase Stabilizes the Catalytic Center and Alters the Dynamics of the Specificity Determining Ω Loop

DOE PAGES

Simakov, Nikolay; Leonard, David A.; Smith, Jeremy C.; ...

2016-09-26

Widespread antibiotic resistance, particularly when mediated by broad-spectrum β-lactamases, has major implications for public health. Substitutions in the active site often allow broad-spectrum enzymes to accommodate diverse types of β-lactams. Substitutions observed outside the active site are thought to compensate for the loss of thermal stability. The OXA-1 clade of class D β-lactamases contains a pair of conserved cysteines located outside the active site that forms a disulfide bond in the periplasm. In this paper, the effect of the distal disulfide bond on the structure and dynamics of OXA-1 was investigated via 4 μs molecular dynamics simulations. The results revealmore » that the disulfide promotes the preorganized orientation of the catalytic residues and affects the conformation of the functionally important Ω loop. Furthermore, principal component analysis reveals differences in the global dynamics between the oxidized and reduced forms, especially in the motions involving the Ω loop. A dynamical network analysis indicates that, in the oxidized form, in addition to its role in ligand binding, the KTG family motif is a central hub of the global dynamics. Finally, as activity of OXA-1 has been measured only in the reduced form, we suggest that accurate assessment of its functional profile would require oxidative conditions mimicking periplasm.« less

Proteomic analyses for profiling regulated proteins/enzymes by Fucus vesiculosus fucoidan in B16 melanoma cells: A combination of enzyme kinetics functional study.

PubMed

Wang, Zhi-Jiang; Zheng, Li; Yang, Jun-Mo; Kang, Yani; Park, Yong-Doo

2018-06-01

Fucoidans are complex sulfated polysaccharides that have a wide range of biological activities. Previously, we reported the various effects of Fucus vesiculosus fucoidan on tyrosinase and B16 melanoma cells. In this study, to identify fucoidan-targeted proteins in B16 melanoma cells, we performed a proteomics study and integrated enzyme kinetics. We detected 19 candidate proteins dysregulated by fucoidan treatment. Among the probed proteins, the enzyme kinetics of two candidate enzymes, namely lactate dehydrogenase (LDH) as an upregulated protein and superoxide dismutase (SOD) as a downregulated enzyme, were determined. The enzyme kinetics results showed that Fucus vesiculosus fucoidan significantly inhibited LDH catalytic function while it did not affect SOD activity even at a high dose, while only slightly decreased activity (up to 10%) at a low dose. Based on our previous and present observations, fucoidan could inhibit B16 melanoma cells growth via regulating proteins/enzymes expression levels such as LDH and SOD known as cell survival biomarkers. Interestingly, both expression level and enzyme catalytic activity of LDH were regulated by fucoidan, which could directly induce the apoptotic effect on B16 melanoma cells along with SOD downregulation. This study highlights how combining proteomics with enzyme kinetics can yield valuable insights into fucoidan targets. Copyright © 2018 Elsevier B.V. All rights reserved.

Organoelement chemistry: promising growth areas and challenges

NASA Astrophysics Data System (ADS)

Abakumov, G. A.; Piskunov, A. V.; Cherkasov, V. K.; Fedushkin, I. L.; Ananikov, V. P.; Eremin, D. B.; Gordeev, E. G.; Beletskaya, I. P.; Averin, A. D.; Bochkarev, M. N.; Trifonov, A. A.; Dzhemilev, U. M.; D'yakonov, V. A.; Egorov, M. P.; Vereshchagin, A. N.; Syroeshkin, M. A.; Jouikov, V. V.; Muzafarov, A. M.; Anisimov, A. A.; Arzumanyan, A. V.; Kononevich, Yu N.; Temnikov, M. N.; Sinyashin, O. G.; Budnikova, Yu H.; Burilov, A. R.; Karasik, A. A.; Mironov, V. F.; Storozhenko, P. A.; Shcherbakova, G. I.; Trofimov, B. A.; Amosova, S. V.; Gusarova, N. K.; Potapov, V. A.; Shur, V. B.; Burlakov, V. V.; Bogdanov, V. S.; Andreev, M. V.

2018-05-01

The chemistry of organoelement compounds is now one of the most rapidly developing fields of research, regarding both fundamental science and solution of applied problems. This review covers a variety of classes of organoelement compounds, ranging from molecules with highly labile carbon–element bonds to compounds with stable bonds that form the basis of novel structural materials and demonstrates their role in scientific research and industrial production. The use of Grignard reagents in modern organic synthesis and application of catalytic cyclomagnesiation and cycloalumination reactions for the preparation of difficult-to-access metallacycles are considered. The electron transfer processes in redox-active derivatives of Group 14 elements and the role of radical ions in these processes are discussed. Considerable attention is paid to organometallic compounds, first of all, as catalysts; the dynamic nature of catalysis with these compounds is noted. Unusual strained metallacycles of high thermal stability, zirconacyclocumulenes, which also exhibit catalytic activity, are described. Complexes with redox-active ligands that substantially affect the reactivity of the metal centre and directly participate in reactions with various substrates as well as organometallic compounds of lanthanides are considered. Modern environmentally benign methods for the synthesis of organosilicon compounds and production of unique materials based on them are discussed. Particular Sections are devoted to organophosphorus compounds, including those exhibiting therapeutic properties and possessing unusual optical characteristics, and organic chalcogen compounds, which find use as ligands and biologically active molecules. The bibliography includes 1045 references.

Effect of sulfation on the surface activity of CaO for N2O decomposition

NASA Astrophysics Data System (ADS)

Wu, Lingnan; Hu, Xiaoying; Qin, Wu; Dong, Changqing; Yang, Yongping

2015-12-01

Limestone addition to circulating fluidized bed boilers for sulfur removal affects nitrous oxide (N2O) emission at the same time, but mechanism of how sulfation process influences the surface activity of CaO for N2O decomposition remains unclear. In this paper, we investigated the effect of sulfation on the surface properties and catalytic activity of CaO for N2O decomposition using density functional theory calculations. Sulfation of CaO (1 0 0) surface by the adsorption of a single gaseous SO2 or SO3 molecule forms stable local CaSO3 or CaSO4 on the CaO (1 0 0) surface with strong hybridization between the S atom of SOx and the surface O anion. The formed local CaSO3 increases the barrier energy of N2O decomposition from 0.989 eV (on the CaO (1 0 0) surface) to 1.340 eV, and further sulfation into local CaSO4 remarkably increases the barrier energy to 2.967 eV. Sulfation from CaSO3 into CaSO4 is therefore the crucial step for deactivating the surface activity for N2O decomposition. Completely sulfated CaSO4 (0 0 1) and (0 1 0) surfaces further validate the negligible catalytic ability of CaSO4 for N2O decomposition.

Cathodic electrochemical activation of Co3O4 nanoarrays: a smart strategy to significantly boost the hydrogen evolution activity.

PubMed

Yang, Li; Zhou, Huang; Qin, Xin; Guo, Xiaodong; Cui, Guanwei; Asiri, Abdullah M; Sun, Xuping

2018-02-22

Co(hydro)oxides show unsatisfactory catalytic activity for the hydrogen evolution reaction (HER) in alkaline media, and it is thus highly desirable but still remains a challenge to design and develop Co(hydro)oxide derived materials as superb hydrogen-evolving catalysts using a facile, rapid and less energy-intensive method. Here, we propose a cathodic electrochemical activation strategy toward greatly boosted HER activity of a Co 3 O 4 nanoarray via room-temperature cathodic polarization in sodium hypophosphite solution. After activation, the overpotential significantly decreases from 260 to 73 mV to drive a geometrical catalytic current density of 10 mA cm -2 in 1.0 M KOH. Notably, this activated electrode also shows strong long-term electrochemical durability with the retention of its catalytic activity at 100 mA cm -2 for at least 40 h.

Baicalin and scutellarin are proteasome inhibitors that specifically target chymotrypsin-like catalytic activity.

PubMed

Wu, Yi-Xin; Sato, Eiji; Kimura, Wataru; Miura, Naoyuki

2013-09-01

Baicalin and scutellarin are the major active principal flavonoids extracted from the Chinese herbal medicines Scutellaria baicalensis and Erigeron breviscapus (Vant.) Hand-Mazz. It has recently been reported that baicalin and scutellarin have antitumor activity. However, the mechanisms of action are unknown. We previously reported that some flavonoids have a specific role in the inhibition of the activity of proteasome subunits and induced apoptosis in tumor cells. To further investigate these pharmacological effects, we examined the inhibitory activity of baicalin and scutellarin on the extracted proteasomes from mice and cancer cells. Using fluorogenic substrates for proteasome catalytic subunits, we found that baicalin and scutellarin specifically inhibited chymotrypsin-like activity but did not inhibit trypsin-like and peptidyl-glutamyl peptide hydrolyzing activities. These data suggested that baicalin and scutellarin specifically inhibit chymotrypsin-like catalytic activity in the proteasome. Copyright © 2012 John Wiley & Sons, Ltd.

Sumoylation promotes optimal APC/C Activation and Timely Anaphase.

PubMed

Lee, Christine C; Li, Bing; Yu, Hongtao; Matunis, Michael J

2018-03-08

The Anaphase Promoting Complex/Cyclosome (APC/C) is a ubiquitin E3 ligase that functions as the gatekeeper to mitotic exit. APC/C activity is controlled by an interplay of multiple pathways during mitosis, including the spindle assembly checkpoint (SAC), that are not yet fully understood. Here, we show that sumoylation of the APC4 subunit of the APC/C peaks during mitosis and is critical for timely APC/C activation and anaphase onset. We have also identified a functionally important SUMO interacting motif in the cullin-homology domain of APC2 located near the APC4 sumoylation sites and APC/C catalytic core. Our findings provide evidence of an important regulatory role for SUMO modification and binding in affecting APC/C activation and mitotic exit. © 2018, Lee et al.

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.

Recent progress in asymmetric bifunctional catalysis using multimetallic systems.

PubMed

Shibasaki, Masakatsu; Kanai, Motomu; Matsunaga, Shigeki; Kumagai, Naoya

2009-08-18

The concept of bifunctional catalysis, wherein both partners of a bimolecular reaction are simultaneously activated, is very powerful for designing efficient asymmetric catalysts. Catalytic asymmetric processes are indispensable for producing enantiomerically enriched compounds in modern organic synthesis, providing more economical and environmentally benign results than methods requiring stoichiometric amounts of chiral reagents. Extensive efforts in this field have produced many asymmetric catalysts, and now a number of reactions can be rendered asymmetric. We have focused on the development of asymmetric catalysts that exhibit high activity, selectivity, and broad substrate generality under mild reaction conditions. Asymmetric catalysts based on the concept of bifunctional catalysis have emerged as a particularly effective class, enabling simultaneous activation of multiple reaction components. Compared with conventional catalysts, bifunctional catalysts generally exhibit enhanced catalytic activity and higher levels of stereodifferentiation under milder reaction conditions, attracting much attention as next-generation catalysts for prospective practical applications. In this Account, we describe recent advances in enantioselective catalysis with bifunctional catalysts. Since our identification of heterobimetallic rare earth-alkali metal-BINOL (REMB) complexes, we have developed various types of bifunctional multimetallic catalysts. The REMB catalytic system is effective for catalytic asymmetric Corey-Chaykovsky epoxidation and cyclopropanation. A dinucleating Schiff base has emerged as a suitable multidentate ligand for bimetallic catalysts, promoting catalytic syn-selective nitro-Mannich, anti-selective nitroaldol, and Mannich-type reactions. The sugar-based ligand GluCAPO provides a suitable platform for polymetallic catalysts; structural elucidation revealed that their higher order polymetallic structures are a determining factor for their function in the catalytic asymmetric Strecker reaction. Rational design identified a related ligand, FujiCAPO, which exhibits superior performance in catalytic asymmetric conjugate addition of cyanide to enones and a catalytic asymmetric Diels-Alder-type reaction. The combination of an amide-based ligand with a rare earth metal constitutes a unique catalytic system: the ligand-metal association is in equilibrium because of structural flexibility. These catalytic systems are effective for asymmetric amination of highly coordinative substrate as well as for Mannich-type reaction of alpha-cyanoketones, in which hydrogen bonding cooperatively contributes to substrate activation and stereodifferentiation. Most of the reactions described here generate stereogenic tetrasubstituted carbons or quaternary carbons, noteworthy accomplishments even with modern synthetic methods. Several reactions have been incorporated into the asymmetric synthesis of therapeutics (or their candidate molecules) such as Tamiflu, AS-3201 (ranirestat), GRL-06579A, and ritodrine, illustrating the usefulness of bifunctional asymmetric catalysis.

Metal-Ion Distribution and Oxygen Vacancies That Determine the Activity of Magnetically Recoverable Catalysts in Methanol Synthesis.

PubMed

Oracko, Troy; Jaquish, Rigel; Losovyj, Yaroslav B; Morgan, David Gene; Pink, Maren; Stein, Barry D; Doluda, Valentin Yu; Tkachenko, Olga P; Shifrina, Zinaida B; Grigoriev, Maxim E; Sidorov, Alexander I; Sulman, Esther M; Bronstein, Lyudmila M

2017-10-04

Here, we report on the development of novel Zn-, Zn-Cr-, and Zn-Cu-containing catalysts using magnetic silica (Fe 3 O 4 -SiO 2 ) as the support. Transmission electron microscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy (XPS) showed that the iron oxide nanoparticles are located in mesoporous silica pores and the magnetite (spinel) structure remains virtually unchanged despite the incorporation of Zn and Cr. According to XPS data, the Zn and Cr species are intermixed within the magnetite structure. In the case of the Zn-Cu-containing catalysts, a separate Cu 2 O phase was also observed along with the spinel structure. The catalytic activity of these catalysts was tested in methanol synthesis from syngas (CO + H 2 ). The catalytic experiments showed an improved catalytic performance of Zn- and Zn-Cr-containing magnetic silicas compared to that of the ZnO-SiO 2 catalyst. The best catalytic activity was obtained for the Zn-Cr-containing magnetic catalyst prepared with 1 wt % Zn and Cr each. X-ray absorption spectroscopy demonstrated the presence of oxygen vacancies near Fe and Zn in Zn-containing, and even more in Zn-Cr-containing, magnetic silica (including oxygen vacancies near Cr ions), revealing a correlation between the catalytic properties and oxygen vacancies. The easy magnetic recovery, robust synthetic procedure, and high catalytic activity make these catalysts promising for practical applications.

Enhancement in the catalytic activity of Pd/USY in the heck reaction induced by H2 bubbling.

PubMed

Okumura, Kazu; Tomiyama, Takuya; Moriyama, Sayaka; Nakamichi, Ayaka; Niwa, Miki

2010-12-24

Pd was loaded on ultra stable Y (USY) zeolites prepared by steaming NH(4)-Y zeolite under different conditions. Heck reactions were carried out over the prepared Pd/USY. We found that H₂ bubbling was effective in improving not only the catalytic activity of Pd/USY, but also that of other supported Pd catalysts and Pd(OAc)₂. Moreover, the catalytic activity of Pd/USY could be optimized by choosing appropriate steaming conditions for the preparation of the USY zeolites; Pd loaded on USY prepared at 873 K with 100% H₂O gave the highest activity (TOF = 61,000 h⁻¹), which was higher than that of Pd loaded on other kinds of supports. The prepared Pd/USY catalysts were applicable to the Heck reactions using various kinds of substrates including bromo- and chloro-substituted aromatic and heteroaromatic compounds. Characterization of the acid properties of the USY zeolites revealed that the strong acid site (OH(strong)) generated as a result of steaming had a profound effect on the catalytic activity of Pd.

Electro-catalytic degradation of sulfisoxazole by using graphene anode.

PubMed

Wang, Yanyan; Liu, Shuan; Li, Ruiping; Huang, Yingping; Chen, Chuncheng

2016-05-01

Graphite and graphene electrodes were prepared by using pure graphite as precursor. The electrode materials were characterized by a scanning electron microscope (SEM), X-ray diffraction (XRD) and cyclic voltammetry (CV) measurements. The electro-catalytic activity for degradation of sulfisoxazole (SIZ) was investigated by using prepared graphene or graphite anode. The results showed that the degradation of SIZ was much more rapid on the graphene than that on the graphite electrode. Moreover, the graphene electrode exhibited good stability and recyclability. The analysis on the intermediate products and the measurement of active species during the SIZ degradation demonstrated that indirect oxidation is the dominant mechanism, involving the electro-catalytic generation of OH and O2(-) as the main active oxygen species. This study implies that graphene is a promising potential electrode material for long-term application to electro-catalytic degradation of organic pollutants. Copyright © 2015. Published by Elsevier B.V.

Simple size-controlled synthesis of Au nanoparticles and their size-dependent catalytic activity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suchomel, Petr; Kvitek, Libor; Prucek, Robert

The controlled preparation of Au nanoparticles (NPs) in the size range of 6 to 22 nm is explored in this study. The Au NPs were prepared by the reduction of tetrachloroauric acid using maltose in the presence of nonionic surfactant Tween 80 at various concentrations to control the size of the resulting Au NPs. With increasing concentration of Tween 80 a decrease in the size of produced Au NPs was observed, along with a significant decrease in their size distribution. The size-dependent catalytic activity of the synthesized Au NPs was tested in the reduction of 4-nitrophenol with sodium borohydride, resultingmore » in increasing catalytic activity with decreasing size of the prepared nanoparticles. Eley-Rideal catalytic mechanism emerges as the more probable, in contrary to the Langmuir-Hinshelwood mechanism reported for other noble metal nanocatalysts.« less

Simple size-controlled synthesis of Au nanoparticles and their size-dependent catalytic activity

DOE PAGES

Suchomel, Petr; Kvitek, Libor; Prucek, Robert; ...

2018-03-15

The controlled preparation of Au nanoparticles (NPs) in the size range of 6 to 22 nm is explored in this study. The Au NPs were prepared by the reduction of tetrachloroauric acid using maltose in the presence of nonionic surfactant Tween 80 at various concentrations to control the size of the resulting Au NPs. With increasing concentration of Tween 80 a decrease in the size of produced Au NPs was observed, along with a significant decrease in their size distribution. The size-dependent catalytic activity of the synthesized Au NPs was tested in the reduction of 4-nitrophenol with sodium borohydride, resultingmore » in increasing catalytic activity with decreasing size of the prepared nanoparticles. Eley-Rideal catalytic mechanism emerges as the more probable, in contrary to the Langmuir-Hinshelwood mechanism reported for other noble metal nanocatalysts.« less

A virus-based biocatalyst

NASA Astrophysics Data System (ADS)

Carette, Noëlle; Engelkamp, Hans; Akpa, Eric; Pierre, Sebastien J.; Cameron, Neil R.; Christianen, Peter C. M.; Maan, Jan C.; Thies, Jens C.; Weberskirch, Ralf; Rowan, Alan E.; Nolte, Roeland J. M.; Michon, Thierry; van Hest, Jan C. M.

2007-04-01

Virus particles are probably the most precisely defined nanometre-sized objects that can be formed by protein self-assembly. Although their natural function is the storage and transport of genetic material, they have more recently been applied as scaffolds for mineralization and as containers for the encapsulation of inorganic compounds. The reproductive power of viruses has been used to develop versatile analytical methods, such as phage display, for the selection and identification of (bio)active compounds. To date, the combined use of self-assembly and reproduction has not been used for the construction of catalytic systems. Here we describe a self-assembled system based on a plant virus that has its coat protein genetically modified to provide it with a lipase enzyme. Using single-object and bulk catalytic studies, we prove that the virus-anchored lipase molecules are catalytically active. This anchored biocatalyst, unlike man-made supported catalysts, has the capability to reproduce itself in vivo, generating many independent catalytically active copies.

Boosting hot electron flux and catalytic activity at metal-oxide interfaces of PtCo bimetallic nanoparticles.

PubMed

Lee, Hyosun; Lim, Juhyung; Lee, Changhwan; Back, Seoin; An, Kwangjin; Shin, Jae Won; Ryoo, Ryong; Jung, Yousung; Park, Jeong Young

2018-06-08

Despite numerous studies, the origin of the enhanced catalytic performance of bimetallic nanoparticles (NPs) remains elusive because of the ever-changing surface structures, compositions, and oxidation states of NPs under reaction conditions. An effective strategy for obtaining critical clues for the phenomenon is real-time quantitative detection of hot electrons induced by a chemical reaction on the catalysts. Here, we investigate hot electrons excited on PtCo bimetallic NPs during H 2 oxidation by measuring the chemicurrent on a catalytic nanodiode while changing the Pt composition of the NPs. We reveal that the presence of a CoO/Pt interface enables efficient transport of electrons and higher catalytic activity for PtCo NPs. These results are consistent with theoretical calculations suggesting that lower activation energy and higher exothermicity are required for the reaction at the CoO/Pt interface.

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. Copyright © 2016 Elsevier Inc. All rights reserved.

Low Pt content direct methanol fuel cell anode catalyst: nanophase PtRuNiZr

NASA Technical Reports Server (NTRS)

Whitacre, Jay F. (Inventor); Narayanan, Sekharipuram R. (Inventor)

2010-01-01

A method for the preparation of a metallic material having catalytic activity that includes synthesizing a material composition comprising a metal content with a lower Pt content than a binary alloy containing Pt but that displays at least a comparable catalytic activity on a per mole Pt basis as the binary alloy containing Pt; and evaluating a representative sample of the material composition to ensure that the material composition displays a property of at least a comparable catalytic activity on a per mole Pt basis as a representative binary alloy containing Pt. Furthermore, metallic compositions are disclosed that possess substantial resistance to corrosive acids.

Investigating the Synthesis, Structure, and Catalytic Properties of Versatile Gold-Based Nanocatalvsts

NASA Astrophysics Data System (ADS)

Pretzer, Lori A.

Transition metal nanomaterials are used to catalyze many chemical reactions, including those key to environmental, medicinal, and petrochemical fields. Improving their catalytic properties and lifetime would have significant economic and environmental rewards. Potentially expedient options to make such advancements are to alter the shape, size, or composition of transition metal nanocatalysts. This work investigates the relationships between structure and catalytic properties of synthesized Au, Pd-on-Au, and Au-enzyme model transition metal nanocatalysts. Au and Pd-on-Au nanomaterials were studied due to their wide-spread application and structure-dependent electronic and geometric properties. The goal of this thesis is to contribute design procedures and synthesis methods that enable the preparation of more efficient transition metal nanocatalysts. The influence of the size and composition of Pd-on-Au nanoparticles (NPs) was systematically investigated and each was found to affect the catalyst's surface structure and catalytic properties. The catalytic hydrodechlorination of trichloroethene and reduction of 4-nitrophenol by Pd-on-Au nanoparticles were investigated as these reactions are useful for environmental and pharmaceutical synthesis applications, respectively. Structural characterization revealed that the dispersion and oxidation state of surface Pd atoms are controlled by the Au particle size and concentration of Pd. These structural changes are correlated with observed Pd-on-Au NP activities for both probe reactions, providing new insight into the structure-activity relationships of bimetallic nanocatalysts. Using the structure-dependent electronic properties of Au NPs, a new type of light-triggered biocatalyst was prepared and used to remotely control a model biochemical reaction. This biocatalyst consists of a model thermophilic glucokinase enzyme covalently attached to the surface of Au nanorods. The rod-like shape of the Au nanoparticles made the thermophilic-enzyme complexes responsive to near infrared electromagnetic radiation, which is absorbed minimally by biological tissues. When enzyme-Au nanorod complexes are illuminated with a near-infrared laser, thermal energy is generated which activates the thermophilic enzyme. Enzyme-Au nanorod complexes encapsulated in calcium alginate are reusable and stable for several days, making them viable for industrial applications. Lastly, highly versatile Au nanoparticles with diameters of ~3-12 nm were prepared using carbon monoxide (CO) to reduce a Au salt precursor onto preformed catalytic Au particles. Compared to other reducing agents used to generate metallic NPs, CO can be used at room temperature and its oxidized form does not interfere with the colloidal stability of NPs suspended in water. Controlled synthesis of different sized particles was verified through detailed ultraviolet-visible spectroscopy, small angle X-ray scattering, and transmission electron microscopy measurements. This synthesis method should be extendable to other monometallic and multimetallic compositions and shapes, and can be improved by using preformed particles with a narrower size distribution.

Protein Surface Softness Is the Origin of Enzyme Cold-Adaptation of Trypsin

PubMed Central

Isaksen, Geir Villy; Åqvist, Johan; Brandsdal, Bjørn Olav

2014-01-01

Life has effectively colonized most of our planet and extremophilic organisms require specialized enzymes to survive under harsh conditions. Cold-loving organisms (psychrophiles) express heat-labile enzymes that possess a high specific activity and catalytic efficiency at low temperatures. A remarkable universal characteristic of cold-active enzymes is that they show a reduction both in activation enthalpy and entropy, compared to mesophilic orthologs, which makes their reaction rates less sensitive to falling temperature. Despite significant efforts since the early 1970s, the important question of the origin of this effect still largely remains unanswered. Here we use cold- and warm-active trypsins as model systems to investigate the temperature dependence of the reaction rates with extensive molecular dynamics free energy simulations. The calculations quantitatively reproduce the catalytic rates of the two enzymes and further yield high-precision Arrhenius plots, which show the characteristic trends in activation enthalpy and entropy. Detailed structural analysis indicates that the relationship between these parameters and the 3D structure is reflected by significantly different internal protein energy changes during the reaction. The origin of this effect is not localized to the active site, but is found in the outer regions of the protein, where the cold-active enzyme has a higher degree of softness. Several structural mechanisms for softening the protein surface are identified, together with key mutations responsible for this effect. Our simulations further show that single point-mutations can significantly affect the thermodynamic activation parameters, indicating how these can be optimized by evolution. PMID:25165981

Effect of mesoporous g-C3N4 substrate on catalytic oxidation of CO over Co3O4

NASA Astrophysics Data System (ADS)

Yang, Heng; Lv, Kangle; Zhu, Junjiang; Li, Qin; Tang, Dingguo; Ho, Wingkei; Li, Mei; Carabineiro, Sónia A. C.

2017-04-01

Mesoporous graphitic carbon nitride (mpg-CN) was synthesized using Triton X-100, a surfactant containing a hydrophilic polyethylene oxide group and a tert-octyl-phenyl hydrophobic moiety, as a soft template. The obtained mpg-CN was used as a support for Co3O4, and this supported catalyst was used for CO oxidation. The effects of the amount of Triton X-100, weight ratio of Co3O4 to mpg-CN and calcination temperature on the catalytic performances for CO oxidation of Co3O4/mpg-CN composites were systematically studied. It was found that the presence of Triton X-100 not only retarded the polymerization of dicyandiamide, but also affected the microstructure of Co3O4. Bubbles formed because of the hydrophobic group of the surfactant Triton X-100 can be act as a soft template for the synthesis of mesoporous g-C3N4. The enhanced catalytic activity of Co3O4/mpg-CN was attributed to a synergistic effect, enlarged BET surface areas, increased Co3+ and lattice oxygen contents, and the porous structure of mpg-CN support. The high stability of 12.5% Co3O4/mpg-CN(1.0) makes it a promising catalyst for practical applications.

Catalytic decomposition of gaseous 1,2-dichlorobenzene over CuOx/TiO₂ and CuOx/TiO₂-CNTs catalysts: Mechanism and PCDD/Fs formation.

PubMed

Wang, Qiu-lin; Huang, Qun-xing; Wu, Hui-fan; Lu, Sheng-yong; Wu, Hai-long; Li, Xiao-dong; Yan, Jian-hua

2016-02-01

Gaseous 1,2-dichlorobenzene (1,2-DCBz) was catalytically decomposed in a fixed-bed catalytic reactor using composite copper-based titanium oxide (CuOx/TiO2) catalysts with different copper ratios. Carbon nanotubes (CNTs) were introduced to produce novel CuOx/TiO2-CNTs catalysts by the sol-gel method. The catalytic performances of CuOx/TiO2 and CuOx/TiO2-CNTs on 1,2-DCBz oxidative destruction under different temperatures (150-350 °C) were experimentally examined and the correlation between catalyst structure and catalytic activity was characterized and the role of oxygen in catalytic reaction was discussed. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) generation during 1,2-DCBz catalytic oxidation by CuOx/TiO2-CNTs composite catalyst was also examined. Results indicate that the 1,2-DCBz destruction/removal efficiencies of CuOx (4 wt%)/TiO2 catalyst at 150 °C and 350 °C with a GHSV of 3400 h(-1) are 59% and 94% respectively and low-temperature (150 °C) catalytic activity of CuOx/TiO2 on 1,2-DCBz oxidation can be improved from 59 to 77% when CNTs are introduced. Furthermore, oxygen either in catalyst or from reaction atmosphere is indispensible in reaction. The former is offered to activate and oxidize the 1,2-DCBz adsorbed on catalyst, thus can be generally consumed during reaction and the oxygen content in catalyst is observed lost from 39.9 to 35.0 wt% after reacting under inert atmosphere; the latter may replenish the vacancy in catalyst created by the consumed oxygen thus extends the catalyst life and raises the destruction/removal efficiency. The introduction of CNTs also increases the Cu(2+)/Cu(+) ratio, chemisorbed oxygen concentration and surface lattice oxygen binding energy which are closely related with catalytic activity. PCDD/Fs is confirmed to be formed when 1,2-DCBz catalytically oxidized by CuOx/TiO2-CNTs composite catalyst with sufficient oxygen (21%), proper temperature (350 °C) and high concentration of 1,2-DCBz feed (120 ppm). Copyright © 2015 Elsevier Ltd. All rights reserved.

Thermo-Responsive Amphiphilic Block Copolymers Stablilized Gold Nanoparticles: Synthesis and High Catalytic Properties.

PubMed

Lü, Jianhua; Yang, Yu; Gao, Junfang; Duan, Haichao; Lü, Changli

2018-06-19

A series of novel well-defined 8-hydroxyquinoline (HQ)-containing thermo-responsive amphiphilic diblock copolymers poly(styrene-co-5-(2-methacryloylethyloxy- methyl)-8-quinolinol)-b-poly(N-isopropylacrylamide) P(St-co-MQ)-b-PNIPAm (P1,2), P(NIPAm- co-MQ)-b-PSt (P3,4) and triblock copolymer poly(N-isopropylacrylamide)-b-poly(methyl- methacrylate-co-5-(2-methacryloylethyloxymethyl)-8-quinolinol)-b-polystyrene PNIPAm-b- P(MMA-co-MQ)-b-PSt (P5) were prepared by reversible addition fragmentation chain transfer (RAFT) polymerization, and their self-assembly behaviors were studied. The block copolymers P1-P5 stabilized gold nanoparticles (Au@P1-Au@P5) with small size and narrow distribution were obtained through in situ reduction of gold precursors in aqueous solution of polymer micelles with HQ as the coordination groups. The resulting Au@P nanohybrids possessed excellent catalytic activities for the reduction of nitrophenols using NaBH4. The size, morphology and surface chemistry of Au NPs could be controlled by adjusting the structure of block polymers with HQ in different block positions, which plays an important role in the catalytic properties. It was found that longer chain length of hydrophilic or hydrophobic segments of block copolymers were beneficial to elevate the catalytic activity of Au NPs for the reduction of nitrophenols, and the spherical nanoparticles (Au@P5) stabilized with triblock copolymer exhibit higher catalytic performance. Surprisingly, the gold nanowires (Au@P4) produced with P4 have a highest catalytic activity due to large abundance of grain boundaries. Excellent thermo-responsive behaviors for catalytic reaction make the as-prepared Au@P hybrids become an environmentally responsive nano-catalytic materials.

Influence of peracetic acid modification on the physicochemical properties of activated carbon and its performance in the ozone-catalytic oxidation of gaseous benzene

NASA Astrophysics Data System (ADS)

Fang, Ruimei; Huang, Haibao; Huang, Wenjun; Ji, Jian; Feng, Qiuyu; Shu, Yajie; Zhan, Yujie; Liu, Gaoyuan; Xie, Ruijie

2017-10-01

Coal based activated carbon (AC) was pretreated by peracetic acid solution and used for supporting Mn catalyst towards oxidation of gaseous benzene by catalytic ozonation. The as-obtained activated carbon was characterized by XPS, BET, SEM, and TG technologies. It indicates that peracetic acid solution modification not only raised the quantity of chemisorbed oxygen or water, and hydroxyl group on activated carbon material surface, but also increased the specific surface area and benzene adsorption capacity of activated carbon. Benzene could be completely removed in 300 min and CO2 selectivity reached to 61.9% over Mn/AC-modified catalyst. A possible catalytic ozonation mechanism of activated carbon which was treated by peracetic acid solution supported Mn catalyst for oxidation of benzene was proposed.

Catalytic fast pyrolysis of biomass impregnated with potassium phosphate in a hydrogen atmosphere for the production of phenol and activated carbon

NASA Astrophysics Data System (ADS)

Lu, Qiang; Zhang, Zhen-xi; Wang, Xin; Guo, Hao-qiang; Cui, Min-shu; Yang, Yong-ping

2018-02-01

A new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K3PO4 in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K3PO4 and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K3PO4 at 550 oC in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using CO2 activation method, the specific surface area was as high as 1605 m2/g.

Assessment of ten density functionals through the use of local hyper-softness to get insights about the catalytic activity : Iron-based organometallic compounds for ethylene polymerization as testing molecules.

PubMed

Martínez-Araya, Jorge I; Glossman-Mitnik, Daniel

2018-01-18

Ten functionals were used to assess their capability to compute a local reactivity descriptor coming from the Conceptual Density Functional Theory on a group of iron-based organometallic compounds that have been synthesized by Zohuri, G.H. et al. in 2010; these compounds bear the following substituent groups: H-, O 2 N- and CH 3 O- at the para position of the pyridine ring and their catalytic activities were experimentally measured by these authors. The present work involved a theoretical analysis applied on the aforementioned iron-based compounds thus leading to suggest a new 2,6-bis(imino)pyridine catalyst based on iron(II) bearing a fluorine atom whose possible catalytic activity is suggested to be near the catalytic activity of the complex bearing a hydrogen atom as a substituent group by means of the so called local hyper-softness (LHS) thus opening a chance to estimate a possible value of catalytic activity for a new catalyst that has not been synthesized yet without simulating the entire process of ethylene polymerization. Since Conceptual DFT is not a predictive theory, but rather interpretative, an analysis of the used reactivity descriptor and its dependence upon the level of theory was carried in the present work, thus revealing that care should be taken when DFT calculations are used for these purposes.

Structural insights into the catalytic mechanism of a family 18 exo-chitinase

PubMed Central

van Aalten, D. M. F.; Komander, D.; Synstad, B.; Gåseidnes, S.; Peter, M. G.; Eijsink, V. G. H.

2001-01-01

Chitinase B (ChiB) from Serratia marcescens is a family 18 exo-chitinase whose catalytic domain has a TIM-barrel fold with a tunnel-shaped active site. We have solved structures of three ChiB complexes that reveal details of substrate binding, substrate-assisted catalysis, and product displacement. The structure of an inactive ChiB mutant (E144Q) complexed with a pentameric substrate (binding in subsites −2 to +3) shows closure of the “roof” of the active site tunnel. It also shows that the sugar in the −1 position is distorted to a boat conformation, thus providing structural evidence in support of a previously proposed catalytic mechanism. The structures of the active enzyme complexed to allosamidin (an analogue of a proposed reaction intermediate) and of the active enzyme soaked with pentameric substrate show events after cleavage of the glycosidic bond. The latter structure shows reopening of the roof of the active site tunnel and enzyme-assisted product displacement in the +1 and +2 sites, allowing a water molecule to approach the reaction center. Catalysis is accompanied by correlated structural changes in the core of the TIM barrel that involve conserved polar residues whose functions were hitherto unknown. These changes simultaneously contribute to stabilization of the reaction intermediate and alternation of the pKa of the catalytic acid during the catalytic cycle. PMID:11481469

Catalytic Fast Pyrolysis of Biomass Impregnated with Potassium Phosphate in a Hydrogen Atmosphere for the Production of Phenol and Activated Carbon

PubMed Central

Lu, Qiang; Zhang, Zhen-xi; Wang, Xin; Guo, Hao-qiang; Cui, Min-shu; Yang, Yong-ping

2018-01-01

A new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K3PO4 in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K3PO4 and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K3PO4 at 550°C in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using CO2 activation method, the specific surface area was as high as 1,605 m2/g. PMID:29515994

Catalytic Fast Pyrolysis of Biomass Impregnated with Potassium Phosphate in a Hydrogen Atmosphere for the Production of Phenol and Activated Carbon.

PubMed

Lu, Qiang; Zhang, Zhen-Xi; Wang, Xin; Guo, Hao-Qiang; Cui, Min-Shu; Yang, Yong-Ping

2018-01-01

A new technique was proposed to co-produce phenol and activated carbon (AC) from catalytic fast pyrolysis of biomass impregnated with K 3 PO 4 in a hydrogen atmosphere, followed by activation of the pyrolytic solid residues. Lab-scale catalytic fast pyrolysis experiments were performed to quantitatively determine the pyrolytic product distribution, as well as to investigate the effects of several factors on the phenol production, including pyrolysis atmosphere, catalyst type, biomass type, catalytic pyrolysis temperature, and catalyst impregnation content. In addition, the pyrolytic solid residues were activated to prepare ACs with high specific surface areas. The results indicated that phenol could be obtained due to the synergistic effects of K 3 PO 4 and hydrogen atmosphere, with the yield and selectivity reaching 5.3 wt% and 17.8% from catalytic fast pyrolysis of poplar wood with 8 wt% K 3 PO 4 at 550°C in a hydrogen atmosphere. This technique was adaptable to different woody materials for phenol production. Moreover, gas product generated from the pyrolysis process was feasible to be recycled to provide the hydrogen atmosphere, instead of extra hydrogen supply. In addition, the pyrolytic solid residue was suitable for AC preparation, using CO 2 activation method, the specific surface area was as high as 1,605 m 2 /g.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mihaela Grigore; Richard Sakurovs; David French

Gasification of coke contributes to its degradation in the blast furnace. In this study, the effect of gasification on the inherent catalytic minerals in cokes and their reciprocal influence on gasification are investigated. The catalytic mineral phases identified in the cokes used in this study were metallic iron, iron sulfides, and iron oxides. Metallic iron and pyrrhotite were rapidly oxidized during gasification to iron oxide. The catalysts had a strong influence on the apparent rates at the initial stages of reaction. As gasification proceeds, their effect on the reaction rate diminishes as a result of reducing the surface contact betweenmore » catalyst and carbon matrix because of carbon consumption around the catalyst particles; with extended burnout the reactivity of the coke becomes increasingly dependent on surface area. The reaction rate in the initial stages was also influenced by the particle size of the catalytic minerals; for a given catalytic iron level, the cokes whose catalytic minerals were more finely dispersed had a higher apparent reaction rate than cokes containing larger catalytic particles. Iron, sodium, and potassium in the amorphous phase did not appear to affect the reaction rate. 40 refs., 16 figs., 6 tabs.« less

N- versus C-domain selectivity of catalytic inactivation of human angiotensin converting enzyme by lisinopril-coupled transition metal chelates.

PubMed

Hocharoen, Lalintip; Joyner, Jeff C; Cowan, J A

2013-12-27

The N- and C-terminal domains of human somatic angiotensin I converting enzyme (sACE-1) demonstrate distinct physiological functions, with resulting interest in the development of domain-selective inhibitors for specific therapeutic applications. Herein, the activity of lisinopril-coupled transition metal chelates was tested for both reversible binding and irreversible catalytic inactivation of each domain of sACE-1. C/N domain binding selectivity ratios ranged from 1 to 350, while rates of irreversible catalytic inactivation of the N- and C-domains were found to be significantly greater for the N-domain, suggesting a more optimal orientation of M-chelate-lisinopril complexes within the active site of the N-domain of sACE-1. Finally, the combined effect of binding selectivity and inactivation selectivity was assessed for each catalyst (double-filter selectivity factors), and several catalysts were found to cause domain-selective catalytic inactivation. The results of this study demonstrate the ability to optimize the target selectivity of catalytic metallopeptides through both binding and catalytic factors (double-filter effect).

Imidazolium- and Triazine-Based Porous Organic Polymers for Heterogeneous Catalytic Conversion of CO2 into Cyclic Carbonates.

PubMed

Zhong, Hong; Su, Yanqing; Chen, Xingwei; Li, Xiaoju; Wang, Ruihu

2017-12-22

CO 2 adsorption and concomitant catalytic conversion into useful chemicals are promising approaches to alleviate the energy crisis and effects of global warming. This is highly desirable for developing new types of heterogeneous catalytic materials containing CO 2 -philic groups and catalytic active sites for CO 2 chemical transformation. Here, we present an imidazolium- and triazine-based porous organic polymer with counter chloride anion (IT-POP-1). The porosity and CO 2 affinity of IT-POP-1 may be modulated at the molecular level through a facile anion-exchange strategy. Compared with the post-modified polymers with iodide and hexafluorophosphate anions, IT-POP-1 possesses the highest surface area and the best CO 2 uptake capacity with excellent adsorption selectivity over N 2 . The roles of the task-specific components such as triazine, imidazolium, hydroxyl, and counter anions in CO 2 absorption and catalytic performance were illustrated. IT-POP-1 exhibits the highest catalytic activity and excellent recyclability in solvent- and additive-free cycloaddition reaction of CO 2 with epoxides. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Purification and characterization of protein phosphatase 2A from petals of the tulip Tulipa gesnerina.

PubMed

Azad, Md Abul Kalam; Sawa, Yoshihiro; Ishikawa, Takahiro; Shibata, Hitoshi

2006-11-30

The holoenzyme of protein phosphatase (PP) from tulip petals was purified by using hydrophobic interaction, anion exchange and microcystin affinity chromatography to analyze activity towards p-nitrophenyl phosphate (p-NPP). The catalytic subunit of PP was released from its endogenous regulatory subunits by ethanol precipitation and further purified. Both preparations were characterized by immunological and biochemical approaches to be PP2A. On SDS-PAGE, the final purified holoenzyme preparation showed three protein bands estimated at 38, 65, and 75 kDa while the free catalytic subunit preparation showed only the 38 kDa protein. In both preparations, the 38 kDa protein was identified immunologically as the catalytic subunit of PP2A by using a monoclonal antibody against the PP2A catalytic subunit. The final 623- and 748- fold purified holoenzyme and the free catalytic preparations, respectively, exhibited high sensitivity to inhibition by 1 nM okadaic acid when activity was measured with p-NPP. The holoenzyme displayed higher stimulation in the presence of ammonium sulfate than the free catalytic subunit did by protamine, thereby suggesting different enzymatic behaviors.

Hydrophobic and hydrophilic nanosheet catalysts with high catalytic activity and recycling stability through control of the outermost ligand

NASA Astrophysics Data System (ADS)

Ko, Younji; Kim, Donghee; Kwon, Cheong Hoon; Cho, Jinhan

2018-04-01

In this study, we introduce hydrophobic and hydrophilic graphene oxide nanosheet (GON) catalysts prepared by consecutive ligand replacement of hydrophobically stabilized magnetic and catalytic nanoparticles (NPs); it exhibits high catalytic activity, fast magnetic response, and good dispersion in both nonpolar and aqueous media, allowing high loading amount of magnetic and catalytic NPs onto GON sheets. More specifically, these GON catalysts showed a high product yield of 66-99% and notable recyclability (93% of the initial product yield after 10 reaction cycles) in a Suzuki-Miyaura reaction in nonpolar media, outperforming the performance of the conventional hydrophilic GON catalysts. Additional coating of a hydrophilic layer onto GON catalysts also showed the notable performance (product yield ∼99%) in catalytic reactions performed in aqueous media. Given that ligand-controlled catalytic NPs adsorbed onto 2D nanosheets can be used as hydrophobic and hydrophilic stabilizers as well as catalysts, our approach can provide a tool for developing and designing 2D-nanosheet catalysts with high performance in nonpolar and polar media.

Gold nanoparticle-catalyzed environmentally benign deoxygenation of epoxides to alkenes.

PubMed

Noujima, Akifumi; Mitsudome, Takato; Mizugaki, Tomoo; Jitsukawa, Koichiro; Kaneda, Kiyotomi

2011-09-28

We have developed a highly efficient and green catalytic deoxygenation of epoxides to alkenes using gold nanoparticles (NPs) supported on hydrotalcite [HT: Mg(6)Al(2)CO(3)(OH)(16)] (Au/HT) with alcohols, CO/H(2)O or H(2) as the reducing reagent. Various epoxides were selectively converted to the corresponding alkenes. Among the novel metal NPs on HT, Au/HT was found to exhibit outstanding catalytic activity for the deoxygenation reaction. Moreover, Au/HT can be separated from the reaction mixture and reused with retention of its catalytic activity and selectivity. The high catalytic performance of Au/HT was attributed to the selective formation of Au-hydride species by the cooperative effect between Au NPs and HT.

Over Expression of Wild Type or a Catalytically Dead Mutant of SIRTUIN 6 Does Not Influence NFκB Responses

PubMed Central

McKenary, Joanne; Hayes, Brian; Patel, Champa; Smith, Janet; Bridges, Angela; Fosberry, Andrew; Bhardwaja, Anshu; Mouzon, Bernadette; Chung, Chun-Wa; Barrett, Nathalie; Richmond, Nicola; Modha, Sundip; Solari, Roberto

2012-01-01

SIRT6 is involved in inflammation, aging and metabolism potentially by modulating the functions of both NFκB and HIF1α. Since it is possible to make small molecule activators and inhibitors of Sirtuins we wished to establish biochemical and cellular assays both to assist in drug discovery efforts and to validate whether SIRT6 represents a valid drug target for these indications. We confirmed in cellular assays that SIRT6 can deacetylate acetylated-histone H3 lysine 9 (H3K9Ac), however this deacetylase activity is unusually low in biochemical assays. In an effort to develop alternative assay formats we observed that SIRT6 overexpression had no influence on TNFα induced nuclear translocation of NFκB, nor did it have an effect on nuclear mobility of RelA/p65. In an effort to identify a gene expression profile that could be used to identify a SIRT6 readout we conducted genome-wide expression studies. We observed that overexpression of SIRT6 had little influence on NFκB-dependent genes, but overexpression of the catalytically inactive mutant affected gene expression in developmental pathways. PMID:22792191

Oxidative stress damages rRNA inside the ribosome and differentially affects the catalytic center

PubMed Central

Willi, Jessica; Küpfer, Pascal; Evéquoz, Damien; Fernandez, Guillermo; Polacek, Norbert

2018-01-01

Abstract Intracellular levels of reactive oxygen species (ROS) increase as a consequence of oxidative stress and represent a major source of damage to biomolecules. Due to its high cellular abundance RNA is more frequently the target for oxidative damage than DNA. Nevertheless the functional consequences of damage on stable RNA are poorly understood. Using a genome-wide approach, based on 8-oxo-guanosine immunoprecipitation, we present evidence that the most abundant non-coding RNA in a cell, the ribosomal RNA (rRNA), is target for oxidative nucleobase damage by ROS. Subjecting ribosomes to oxidative stress, we demonstrate that oxidized 23S rRNA inhibits the ribosome during protein biosynthesis. Placing single oxidized nucleobases at specific position within the ribosome's catalytic center by atomic mutagenesis resulted in markedly different functional outcomes. While some active site nucleobases tolerated oxidative damage well, oxidation at others had detrimental effects on protein synthesis by inhibiting different sub-steps of the ribosomal elongation cycle. Our data provide molecular insight into the biological consequences of RNA oxidation in one of the most central cellular enzymes and reveal mechanistic insight on the role of individual active site nucleobases during translation. PMID:29309687

Accelerating research into bio-based FDCA-polyesters by using small scale parallel film reactors.

PubMed

Gruter, Gert-Jan M; Sipos, Laszlo; Adrianus Dam, Matheus

2012-02-01

High Throughput experimentation has been well established as a tool in early stage catalyst development and catalyst and process scale-up today. One of the more challenging areas of catalytic research is polymer catalysis. The main difference with most non-polymer catalytic conversions is the fact that the product is not a well defined molecule and the catalytic performance cannot be easily expressed only in terms of catalyst activity and selectivity. In polymerization reactions, polymer chains are formed that can have various lengths (resulting in a molecular weight distribution rather than a defined molecular weight), that can have different compositions (when random or block co-polymers are produced), that can have cross-linking (often significantly affecting physical properties), that can have different endgroups (often affecting subsequent processing steps) and several other variations. In addition, for polyolefins, mass and heat transfer, oxygen and moisture sensitivity, stereoregularity and many other intrinsic features make relevant high throughput screening in this field an incredible challenge. For polycondensation reactions performed in the melt often the viscosity becomes already high at modest molecular weights, which greatly influences mass transfer of the condensation product (often water or methanol). When reactions become mass transfer limited, catalyst performance comparison is often no longer relevant. This however does not mean that relevant experiments for these application areas cannot be performed on small scale. Relevant catalyst screening experiments for polycondensation reactions can be performed in very efficient small scale parallel equipment. Both transesterification and polycondensation as well as post condensation through solid-stating in parallel equipment have been developed. Next to polymer synthesis, polymer characterization also needs to be accelerated without making concessions to quality in order to draw relevant conclusions.

Biocatalytically active silCoat-composites entrapping viable Escherichia coli.

PubMed

Findeisen, A; Thum, O; Ansorge-Schumacher, M B

2014-02-01

Application of whole cells in industrial processes requires high catalytic activity, manageability, and viability under technical conditions, which can in principle be accomplished by appropriate immobilization. Here, we report the identification of carrier material allowing exceptionally efficient adsorptive binding of Escherichia coli whole cells hosting catalytically active carbonyl reductase from Candida parapsilosis (CPCR2). With the immobilizates, composite formation with both hydrophobic and hydrophilized silicone was achieved, yielding advanced silCoat-material and HYsilCoat-material, respectively. HYsilCoat-whole cells were viable preparations with a cell loading up to 400 mg(E. coli) · g(-1)(carrier) and considerably lower leaching than native immobilizates. SilCoat-whole cells performed particularly well in neat substrate exhibiting distinctly increased catalytic activity.

Active anatase (0 0 1)-like surface of hydrothermally synthesized titania nanotubes

NASA Astrophysics Data System (ADS)

Chen, Qiang; Mogilevsky, Gregory; Wagner, George W.; Forstater, Jacob; Kleinhammes, Alfred; Wu, Yue

2009-11-01

Using 31P and 13C NMR with DFT calculations we demonstrate the exposed surface of titania nanotubes (TiNTs) is a stable, unterminated anatase (0 0 1)-like surface and is catalytically active under ambient conditions. We find that methanol dissociatively adsorbs on the surface of TiNTs agreeing with the predicted activity of surface dissociation of organic molecules on the crystalline (0 0 1)-anatase surface. We further examined the catalytic activity of anatase power, TiNT, and nanosheets in catalytic hydrolysis of S-[2-(diisopropylamino)ethyl]- O-ethyl methylphosphonothioate (VX) via 31P NMR and demonstrate that titanate-like nanosheets are inactive in the reaction owing to their hydroxylated (0 0 1) surface.

Preparation and Characterization of Mesoporous Nickel derived from Liquid crystalline Template and Evaluation of its Electro catalytic activity towards Methanol Oxidation

NASA Astrophysics Data System (ADS)

Mohanapriya, S.; Renuka devi, R.; Raj, V.

2018-02-01

Mesoporous Nickel has been prepared by electrodeposition using non-ionic surfactant based liquid crystalline template under optimized processing conditions. Physico-chemical properties of mesoporous nickel is systematically characterized through XRD, SEM and AFM analyses. Comparison of electrocatalytic activity of mesoporous nickel with smooth nickel was interrogated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) analyses. Distinctly enhanced electrocatalytic activity with improved surface poisoning resistance related to mesoporous nickel electrode towards methanol oxidation stems from unique mesoporous morphology. This mesoporous morphology with high surface to volume ratio is highly beneficial to promote active catalytic centers to offer readily accessible Pt catalytic sites for MOR, through facilitating mass and electron transports.

The catalytic activity of CoMo/USY on deoxygenation reaction of anisole in a batch reactor

NASA Astrophysics Data System (ADS)

Nugrahaningtyas, K. D.; Putri, I. F.; Heraldy, E.; Hidayat, Y.

2018-04-01

The catalytic hydrodeoxigenation of the bio oil model compounds (biomass pyrolysis results) typically uses sulphide catalysts. In this study, we studied the activity of non-sulphide catalyst, the effect of temperature and reaction time on anisole deoxygenation. The catalytic activity was performed in a batch reactor, using N2 gas at 1 bar of pressure. The product was analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The result showed that the Co-Mo/USY catalyst perform a highest activity and produce pentamethylbenzene, an oxygen free products, when reaction time is 2 hours. The Co-Mo/USY catalysts has the value of the total yield of the product increased with time increase drastically.

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation

NASA Astrophysics Data System (ADS)

Kim, Il Hee; Lee, Hyerim; Yu, Areum; Jeong, Jae Hwan; Lee, Youngmi; Kim, Myung Hwa; Lee, Chongmok; Dok Kim, Young

2018-04-01

NiO/NiCo2O4 nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N2 adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (˜20 m2 g-1) than expected for a flat-surface structure (<15 m2 g-1). Herein, we present a study of the catalytic activity of our novel NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo2O4 is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo2O4 for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo2O4 tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

Synthesis and catalytic activity of electrospun NiO/NiCo2O4 nanotubes for CO and acetaldehyde oxidation.

PubMed

Kim, Il Hee; Lee, Hyerim; Yu, Areum; Jeong, Jae Hwan; Lee, Youngmi; Kim, Myung Hwa; Lee, Chongmok; Kim, Young Dok

2018-04-27

NiO/NiCo 2 O 4 nanotubes with a diameter of approximately 100 nm are synthesized using Ni and Co precursors via electro-spinning and subsequent calcination processes. The tubular structure is confirmed via transmission electron microscopy imaging, whereas the structures and elemental compositions of the nanotubes are determined using x-ray diffraction, energy dispersive x-ray spectroscopy, and x-ray photoelectron spectroscopy. N 2 adsorption isotherm data reveal that the surface of the nanotubes consists of micropores, thereby resulting in a significantly higher surface area (∼20 m 2 g -1 ) than expected for a flat-surface structure (<15 m 2 g -1 ). Herein, we present a study of the catalytic activity of our novel NiO/NiCo 2 O 4 nanotubes for CO and acetaldehyde oxidation. The catalytic activity of NiO/NiCo 2 O 4 is superior to Pt below 100 °C for CO oxidation. For acetaldehyde oxidation, the total oxidation activity of NiO/NiCo 2 O 4 for acetaldehyde is comparable with that of Pt. Coexistence of many under-coordinated Co and Ni active sites in our structure is suggested be related to the high catalytic activity. It is suggested that our novel NiO/NiCo 2 O 4 tubular structures with surface microporosity can be of interest for a variety of applications, including the catalytic oxidation of harmful gases.

Application of a new amidophosphite ligand to Rh-catalyzed asymmetric hydrogenation of β-dehydroamino acid derivatives in supercritical carbon dioxide: activation effect of protic Co-solvents.

PubMed

Lyubimov, Sergey E; Rastorguev, Eugenie A; Davankov, Vadim A

2011-09-01

New chiral amidophosphite ligand was synthesized and tested in the Rh-catalyzed asymmetric hydrogenation of (Z)-β-(acylamino)acrylates in protic solvents and supercritical carbon dioxide (scCO(2) ) The catalytic performance is affected greatly by the acidity of the solvents. Better enantioselectivity (up to 88% ee) was achieved in scCO(2) containing 1,1,1,3,3,3-hexafluoro-2-propanol, compared to neat protic solvents. Copyright © 2011 Wiley-Liss, Inc.

Tetraalykylammonium polyoxoanionic oxidation catalysts

DOEpatents

Ellis, Paul E.; Lyons, James E.; Myers, Jr., Harry K.; Shaikh, Shahid N.

1998-01-01

Alkanes are catalytically oxidized in air or oxygen using iron-substituted polyoxoanions (POAs) of the formula: H.sub.e-z ›(n-C.sub.4 H.sub.9).sub.4 N!.sub.z (XM.sub.11 M'O.sub.39).sup.-e The M' (e.g., iron(III)/iron(II)) reduction potential of the POAs is affected by selection of the central atom X and the framework metal M, and by the number of tetrabutyl-ammonium groups. Decreased Fe(III)/Fe(II) reduction potential has been found to correlate to increased oxidation activity.

Tetraalklylammonium polyoxoanionic oxidation catalysts

DOEpatents

Ellis, P.E.; Lyons, J.E.; Myers, H.K. Jr.; Shaikh, S.N.

1998-10-06

Alkanes are catalytically oxidized in air or oxygen using iron-substituted polyoxoanions (POAs) of the formula: H{sub e{minus}z}[(n-C{sub 4}H{sub 9}){sub 4}N]{sub z}(XM{sub 11}M{prime}O{sub 39}){sup {minus}e}. The M{prime} (e.g., iron(III)/iron(II)) reduction potential of the POAs is affected by selection of the central atom X and the framework metal M, and by the number of tetrabutyl-ammonium groups. Decreased Fe(III)/Fe(II) reduction potential has been found to correlate to increased oxidation activity.

Oxidative Dehydrogenation on Nanocarbon: Insights into the Reaction Mechanism and Kinetics via in Situ Experimental Methods.

PubMed

Qi, Wei; Yan, Pengqiang; Su, Dang Sheng

2018-03-20

Sustainable and environmentally benign catalytic processes are vital for the future to supply the world population with clean energy and industrial products. The replacement of conventional metal or metal oxide catalysts with earth abundant and renewable nonmetallic materials has attracted considerable research interests in the field of catalysis and material science. The stable and efficient catalytic performance of nanocarbon materials was discovered at the end of last century, and these materials are considered as potential alternatives for conventional metal-based catalysts. With its rapid development in the past 20 years, the research field of carbon catalysis has been experiencing a smooth transition from the discovery of novel nanocarbon materials or related new reaction systems to the atomistic-level mechanistic understanding on the catalytic process and the subsequent rational design of the practical catalytic reaction systems. In this Account, we summarize the recent progress in the kinetic and mechanistic studies on nanocarbon catalyzed alkane oxidative dehydrogenation (ODH) reactions. The paper attempts to extract general concepts and basic regularities for carbon catalytic process directing us on the way for rational design of novel efficient metal-free catalysts. The nature of the active sites for ODH reactions has been revealed through microcalorimetric analysis, ambient pressure X-ray photoelectron spectroscopy (XPS) measurement, and in situ chemical titration strategies. The detailed kinetic analysis and in situ catalyst structure characterization suggests that carbon catalyzed ODH reactions involve the redox cycles of the ketonic carbonyl-hydroxyl pairs, and the key physicochemical parameters (activation energy, reaction order, and rate/equilibrium constants, etc.) of the carbon catalytic systems are proposed and compared with conventional transition metal oxide catalysts. The proposal of the intrinsic catalytic activity (TOF) provides the possibility for the fair comparisons of different nanocarbon catalysts and the consequent structure-function relation regularity. Surface modification and heteroatom doping are proved as the most effective strategies to adjust the catalytic property (activity and product selectivity etc.) of the nanocarbon catalysts. Nanocarbon is actually a proper candidate platform helping us to understand the classical catalytic reaction mechanism better, since there is no lattice oxygen and all the catalytic process happens on nanocarbon surface. This Account also exhibits the importance of the in situ structural characterizations for heterogeneous nanocarbon catalysis. The research strategy and methods proposed for carbon catalysts may also shed light on other complicated catalytic systems or fields concerning the applications of nonmetallic materials, such as energy storage and environment protection etc.

Investigating Catalytic Properties of Composite Nanoparticle Assemblies

DTIC Science & Technology

2001-11-01

electrode surfaces, were found to be catalytically active towards electrooxidation of CO and MeOH upon activation. The activation involved partial removal...to proceed under stirring at room temperature for 4 hours. producing a dark-brown solution of DT-encapsulated nanoparticles that was then cleaned in... ethanol or used in the heating treatment. Processing. Highly-monodispersed Au particles (5.3 ±0.3 nm) were prepared by thermally activated treatment of

Catalytic oxidation of VOCs over Mn/TiO2/activated carbon under 185 nm VUV irradiation.

PubMed

Shu, Yajie; Xu, Yin; Huang, Haibao; Ji, Jian; Liang, Shimin; Wu, Muyan; Leung, Dennis Y C

2018-06-04

Volatile organic compounds (VOCs) are regarded as the major contributors to air pollution, and should be strictly regulated. Photocatalytic oxidation (PCO) is of great interest for the removal of VOCs owing to its strong oxidation capability. However, its application is greatly limited by catalytic deactivation. Vacuum Ultraviolet (VUV) irradiation provides a novel way to improve the photocatalytic activity while much O 3 will be generated which may cause secondary pollution. In this study, a multi-functional catalyst of Mn/TiO 2 /activated carbon (AC) was developed to eliminate and utilize O 3 , as well as enhance catalytic oxidation of VOC degradation via ozone-assisted catalytic oxidation (OZCO). The results indicate that Mn modified TiO 2 /AC (i.e. 0.1%Mn/20%TiO 2 /AC) achieved a toluene removal efficiency of nearly 86% with 100% elimination rate of O 3 . With the help of Mn/TiO 2 /AC catalyst, O 3 was catalytically decomposed and transformed into active species of O ( 1 D) and OH, thus enhancing toluene removal. The combination of VUV irradiation with multi-functional catalyst provides a novel and efficient way for the degradation of VOCs. Copyright © 2018 Elsevier Ltd. All rights reserved.

Nanoparticle mediated micromotor motion

NASA Astrophysics Data System (ADS)

Liu, Mei; Liu, Limei; Gao, Wenlong; Su, Miaoda; Ge, Ya; Shi, Lili; Zhang, Hui; Dong, Bin; Li, Christopher Y.

2015-03-01

In this paper, we report the utilization of nanoparticles to mediate the motion of a polymer single crystal catalytic micromotor. Micromotors have been fabricated by directly self-assembling functional nanoparticles (platinum and iron oxide nanoparticles) onto one or both sides of two-dimensional polymer single crystals. We show that the moving velocity of these micromotors in fluids can be readily tuned by controlling the nanoparticles' surface wettability and catalytic activity. A 3 times velocity increase has been achieved for a hydrophobic micromotor as opposed to the hydrophilic ones. Furthermore, we demonstrate that the catalytic activity of platinum nanoparticles inside the micromotor can be enhanced by their synergetic interactions with iron oxide nanoparticles and an electric field. Both strategies lead to dramatically increased moving velocities, with the highest value reaching ~200 μm s-1. By decreasing the nanoparticles' surface wettability and increasing their catalytic activity, a maximum of a ~10-fold increase in the moving speed of the nanoparticle based micromotor can be achieved. Our results demonstrate the advantages of using nanoparticles in micromotor systems.In this paper, we report the utilization of nanoparticles to mediate the motion of a polymer single crystal catalytic micromotor. Micromotors have been fabricated by directly self-assembling functional nanoparticles (platinum and iron oxide nanoparticles) onto one or both sides of two-dimensional polymer single crystals. We show that the moving velocity of these micromotors in fluids can be readily tuned by controlling the nanoparticles' surface wettability and catalytic activity. A 3 times velocity increase has been achieved for a hydrophobic micromotor as opposed to the hydrophilic ones. Furthermore, we demonstrate that the catalytic activity of platinum nanoparticles inside the micromotor can be enhanced by their synergetic interactions with iron oxide nanoparticles and an electric field. Both strategies lead to dramatically increased moving velocities, with the highest value reaching ~200 μm s-1. By decreasing the nanoparticles' surface wettability and increasing their catalytic activity, a maximum of a ~10-fold increase in the moving speed of the nanoparticle based micromotor can be achieved. Our results demonstrate the advantages of using nanoparticles in micromotor systems. Electronic supplementary information (ESI) available: Fig. S1-S5 and Video S1-S3. See DOI: 10.1039/c4nr07558g

Forecasting the zeolite-containing catalyst activity in catalytic cracking technology taking into account the feedstock composition

NASA Astrophysics Data System (ADS)

Ivashkina, Elena; Nazarova, Galina; Shafran, Tatyana; Stebeneva, Valeriya

2017-08-01

The effect of the feedstock composition and the process conditions on the current catalyst activity in catalytic cracking technology using a mathematical model is performed in this research. The mathematical model takes into account the catalyst deactivation by coke for primary and secondary cracking reactions. The investigation results have shown that the feedstock has significant effect on the yield and the content of coke on the catalyst. Thus, the relative catalyst activity is significantly reduced by 7.5-10.7 %. With increasing the catalytic cracking temperature due to the catalyst flow temperature rising, the coke content and the yield per feedstock increase and the catalyst activity decreases by 5.3-7.7%. Rising the process temperature together with the catalyst circulation ratio contributes to increase of the coke yield per feedstock in the catalytic cracking and decrease of the coke content on the catalyst. It is connected with the catalyst flow rising to the riser and the contact time decreasing in the reaction zone. Also, the catalyst activity decreases in the range of 3.8-5.5% relatively to the regenerated catalyst activity (83 %).

BIOTEMPLATING OF TITANIUM DIOXIDE NANOPARTICLES FOR THE GREEN PRODUCTION OF PHOTOCHEMICALLY ACTIVE CATALYSTS: SYNTHESIS, CHARACTERIZATION, AND PHOTOCATALYTIC EVALUATION

EPA Science Inventory

The ability of different nano-sized materials (NSM) to effectively act as active photo-catalytic surfaces has been described for the mineralization/inactivation of many different aqueous pollutants. The reason for their enhanced ability over larger catalytic surfaces owes muc...

Open-mouthed hybrid microcapsules with elevated enzyme loading and enhanced catalytic activity.

PubMed

Shi, Jiafu; Zhang, Shaohua; Wang, Xiaoli; Jiang, Zhongyi

2014-10-25

Open-mouthed hybrid microcapsules (HMCs) are synthesized through a hard-templating method. When utilized for enzyme immobilization and enzymatic catalysis, the open-mouthed HMCs show high enzyme loading capability, enhanced catalytic activity and desirable recycling stability, due to their fully exposed outer and inner surfaces.

Method of maintaining activity of hydrogen-sensing platinum electrode

NASA Technical Reports Server (NTRS)

Harman, J. N., III

1968-01-01

Three-electrode hydrogen sensor containing a platinum electrode maintained in a highly catalytic state, operates with a minimal response time and maximal sensitivity to the hydrogen gas being sensed. Electronic control and readout circuitry reactivates the working electrode of the sensor to a state of maximal catalytic activity.

Catalytic and reactive polypeptides and methods for their preparation and use

DOEpatents

Schultz, Peter

1994-01-01

Catalytic and reactive polypeptides include a binding site specific for a reactant or reactive intermediate involved in a chemical reaction of interest. The polypeptides further include at least one active functionality proximate the binding site, where the active functionality is capable of catalyzing or chemically participating in the chemical reaction in such a way that the reaction rate is enhanced. Methods for preparing the catalytic peptides include chemical synthesis, site-directed mutagenesis of antibody and enzyme genes, covalent attachment of the functionalities through particular amino acid side chains, and the like.

Active and Recyclable Catalytic Synthesis of Indoles by Reductive Cyclization of 2-(2-Nitroaryl)acetonitriles in the Presence of Co-Rh Heterobimetallic Nanoparticles with Atmospheric Hydrogen under Mild Conditions.

PubMed

Choi, Isaac; Chung, Hyunho; Park, Jang Won; Chung, Young Keun

2016-11-04

A cobalt-rhodium heterobimetallic nanoparticle-catalyzed reductive cyclization of 2-(2-nitroaryl)acetonitriles to indoles has been achieved. The tandem reaction proceeds without any additives under the mild conditions (1 atm H 2 and 25 °C). This procedure could be scaled up to the gram scale. The catalytic system is significantly stable under these reaction conditions and could be reused more than ten times without loss of catalytic activity.

Catalytic enantioselective silylation of N-sulfonylimines: asymmetric synthesis of α-amino acids from CO2 via stereospecific carboxylation of α-amino silanes.

PubMed

Mita, Tsuyoshi; Sugawara, Masumi; Saito, Keisuke; Sato, Yoshihiro

2014-06-06

A catalytic enantioselective silylation of N-tert-butylsulfonylimines using a Cu-secondary diamine complex was demonstrated. The resulting optically active α-amino silanes could be carboxylated under a CO2 atmosphere (1 atm) to afford the corresponding α-amino acids in a stereoretentive manner. This two-step sequence provides a new synthetic protocol for optically active α-amino acids from gaseous CO2 and imines in the presence of a catalytic amount of a chiral source.

N-Acetylanthranilate Amidase from Arthrobacter nitroguajacolicus Rü61a, an α/β-Hydrolase-Fold Protein Active towards Aryl-Acylamides and -Esters, and Properties of Its Cysteine-Deficient Variant▿ †

PubMed Central

Kolkenbrock, Stephan; Parschat, Katja; Beermann, Bernd; Hinz, Hans-Jürgen; Fetzner, Susanne

2006-01-01

N-acetylanthranilate amidase (Amq), a 32.8-kDa monomeric amide hydrolase, is involved in quinaldine degradation by Arthrobacter nitroguajacolicus Rü61a. Sequence analysis and secondary structure predictions indicated that Amq is related to carboxylesterases and belongs to the α/β-hydrolase-fold superfamily of enzymes; inactivation of (His6-tagged) Amq by phenylmethanesulfonyl fluoride and diethyl pyrocarbonate and replacement of conserved residues suggested a catalytic triad consisting of S155, E235, and H266. Amq is most active towards aryl-acetylamides and aryl-acetylesters. Remarkably, its preference for ring-substituted analogues was different for amides and esters. Among the esters tested, phenylacetate was hydrolyzed with highest catalytic efficiency (kcat/Km = 208 mM−1 s−1), while among the aryl-acetylamides, o-carboxy- or o-nitro-substituted analogues were preferred over p-substituted or unsubstituted compounds. Hydrolysis by His6Amq of primary amides, lactams, N-acetylated amino acids, azocoll, tributyrin, and the acylanilide and urethane pesticides propachlor, propham, carbaryl, and isocarb was not observed; propanil was hydrolyzed with 1% N-acetylanthranilate amidase activity. The catalytic properties of the cysteine-deficient variant His6AmqC22A/C63A markedly differed from those of His6Amq. The replacements effected some changes in Kms of the enzyme and increased kcats for most aryl-acetylesters and some aryl-acetylamides by factors of about three to eight while decreasing kcat for the formyl analogue N-formylanthranilate by several orders of magnitude. Circular dichroism studies indicated that the cysteine-to-alanine replacements resulted in significant change of the overall fold, especially an increase in α-helicity of the cysteine-deficient protein. The conformational changes may also affect the active site and may account for the observed changes in kinetic properties. PMID:17041061

Combining affinity proteomics and network context to identify new phosphatase substrates and adapters in growth pathways

PubMed Central

Sacco, Francesca; Boldt, Karsten; Calderone, Alberto; Panni, Simona; Paoluzi, Serena; Castagnoli, Luisa; Ueffing, Marius; Cesareni, Gianni

2014-01-01

Protein phosphorylation homoeostasis is tightly controlled and pathological conditions are caused by subtle alterations of the cell phosphorylation profile. Altered levels of kinase activities have already been associated to specific diseases. Less is known about the impact of phosphatases, the enzymes that down-regulate phosphorylation by removing the phosphate groups. This is partly due to our poor understanding of the phosphatase-substrate network. Much of phosphatase substrate specificity is not based on intrinsic enzyme specificity with the catalytic pocket recognizing the sequence/structure context of the phosphorylated residue. In addition many phosphatase catalytic subunits do not form a stable complex with their substrates. This makes the inference and validation of phosphatase substrates a non-trivial task. Here, we present a novel approach that builds on the observation that much of phosphatase substrate selection is based on the network of physical interactions linking the phosphatase to the substrate. We first used affinity proteomics coupled to quantitative mass spectrometry to saturate the interactome of eight phosphatases whose down regulations was shown to affect the activation of the RAS-PI3K pathway. By integrating information from functional siRNA with protein interaction information, we develop a strategy that aims at inferring phosphatase physiological substrates. Graph analysis is used to identify protein scaffolds that may link the catalytic subunits to their substrates. By this approach we rediscover several previously described phosphatase substrate interactions and characterize two new protein scaffolds that promote the dephosphorylation of PTPN11 and ERK by DUSP18 and DUSP26, respectively. PMID:24847354

RuO2 supported NaY zeolite catalysts: Effect of preparation methods on catalytic performance during aerobic oxidation of benzyl alcohol

NASA Astrophysics Data System (ADS)

Jung, Dasom; Lee, Sunwoo; Na, Kyungsu

2017-10-01

The effects of preparation method for RuO2 supported zeolite catalysts on the catalytic consequences during the aerobic oxidation of benzyl alcohol to benzaldehyde were investigated. Three preparation methods, i.e., (i) simultaneous crystallization of the zeolite framework in the presence of RuCl3 (Ru(SC)/NaY), (ii) post ion-exchange with RuCl3 on the zeolite framework (Ru(IE)/NaY), and (iii) post support of preformed Ru metal nanoparticles on the zeolite surface (Ru(PS)/NaY), were used to construct three different RuO2 supported NaY zeolite catalysts. The catalyst performance was investigated as functions of the reaction time and temperature, in correlation with the structural changes of the catalysts, as analyzed by X-ray diffraction (XRD). The results revealed that the catalytic consequences were dramatically affected by the preparation methods. Although similar conversion was achieved with all three catalysts, the turnover frequency (TOF) differed. The Ru(PS)/NaY catalyst exhibited the highest TOF (33-48 h-1), whereas the other catalysts produced much lower TOFs (9-12 h-1). The Ru(PS)/NaY catalyst also had the highest activation energy (Ea) of 48.39 kJ mol-1, whereas the Ru(SC)/NaY and Ru(IE)/NaY catalysts had Ea values of 18.58 and 24.11 kJ mol-1, respectively. Notably, the Ru(PS)/NaY catalyst yielded a significantly higher pre-exponential factor of 5.22 × 105 h-1, which is about 5 orders of magnitude larger than that of the Ru(SC)/NaY catalyst (7.15 × 100 h-1). This suggests that collision between benzyl alcohol and molecular oxygen was very intensive on the Ru(PS)/NaY catalyst, which explains the higher TOF of the Ru(PS)/NaY catalyst relative to the others in spite of the higher Ea value of the former. In terms of recyclability, the pristine crystallinity of the zeolite framework was maintained in the Ru(SC)/NaY catalyst and the RuO2 phase exhibited an insignificant loss of the initial activity up to three catalytic cycles, whereas Ru(PS)/NaY showed slight loss of activity and Ru(IE)/NaY showed a significant loss of activity due to the disappearance of the RuO2 phase.

CH4 dehydrogenation on Cu(1 1 1), Cu@Cu(1 1 1), Rh@Cu(1 1 1) and RhCu(1 1 1) surfaces: A comparison studies of catalytic activity

NASA Astrophysics Data System (ADS)

Zhang, Riguang; Duan, Tian; Ling, Lixia; Wang, Baojun

2015-06-01

In the CVD growth of graphene, the reaction barriers of the dehydrogenation for hydrocarbon molecules directly decide the graphene CVD growth temperature. In this study, density functional theory method has been employed to comparatively probe into CH4 dehydrogenation on four types of Cu(1 1 1) surface, including the flat Cu(1 1 1) surface (labeled as Cu(1 1 1)) and the Cu(1 1 1) surface with one surface Cu atom substituted by one Rh atom (labeled as RhCu(1 1 1)), as well as the Cu(1 1 1) surface with one Cu or Rh adatom (labeled as Cu@Cu(1 1 1) and Rh@Cu(1 1 1), respectively). Our results show that the highest barrier of the whole CH4 dehydrogenation process is remarkably reduced from 448.7 and 418.4 kJ mol-1 on the flat Cu(1 1 1) and Cu@Cu(1 1 1) surfaces to 258.9 kJ mol-1 on RhCu(1 1 1) surface, and to 180.0 kJ mol-1 on Rh@Cu(1 1 1) surface, indicating that the adsorbed or substituted Rh atom on Cu catalyst can exhibit better catalytic activity for CH4 complete dehydrogenation; meanwhile, since the differences for the highest barrier between Cu@Cu(1 1 1) and Cu(1 1 1) surfaces are smaller, the catalytic behaviors of Cu@Cu(1 1 1) surface are very close to the flat Cu(1 1 1) surface, suggesting that the morphology of Cu substrate does not obviously affect the dehydrogenation of CH4, which accords with the reported experimental observations. As a result, the adsorbed or substituted Rh atom on Cu catalyst exhibit a better catalytic activity for CH4 dehydrogenation compared to the pure Cu catalyst, especially on Rh-adsorbed Cu catalyst, we can conclude that the potential of synthesizing high-quality graphene with the help of Rh on Cu foils may be carried out at relatively low temperatures. Meanwhile, the adsorbed Rh atom is the reaction active center, namely, the CVD growth can be controlled by manipulating the graphene nucleation position.

Access channels to the buried active site control substrate specificity in CYP1A P450 enzymes.

PubMed

Urban, Philippe; Truan, Gilles; Pompon, Denis

2015-04-01

A cytochrome P450 active site is buried within the protein molecule and several channels connect the catalytic cavity to the protein surface. Their role in P450 catalysis is still matter of debate. The aim of this study was to understand the possible relations existing between channels and substrate specificity. Time course studies were carried out with a collection of polycyclic substrates of increasing sizes assayed with a library of wild-type and chimeric CYP1A enzymes. This resulted in a matrix of activities sufficiently large to allow statistical analysis. Multivariate statistical tools were used to decipher the correlation between observed activity shifts and sequence segment swaps. The global kinetic behavior of CYP1A enzymes toward polycyclic substrates is significantly different depending on the size of the substrate. Mutations which are close or lining the P450 channels significantly affect this discrimination, whereas mutations distant from the P450 channels do not. Size discrimination is taking place for polycyclic substrates at the entrance of the different P450 access channels. It is thus hypothesized that channels differentiate small from large substrates in CYP1A enzymes, implying that residues located at the surface of the protein may be implied in this differential recognition. Catalysis thus occurs after a two-step recognition process, one at the surface of the protein and the second within the catalytic cavity in enzymes with a buried active site. Copyright © 2014 Elsevier B.V. All rights reserved.

SABER: A computational method for identifying active sites for new reactions

PubMed Central

Nosrati, Geoffrey R; Houk, K N

2012-01-01

A software suite, SABER (Selection of Active/Binding sites for Enzyme Redesign), has been developed for the analysis of atomic geometries in protein structures, using a geometric hashing algorithm (Barker and Thornton, Bioinformatics 2003;19:1644–1649). SABER is used to explore the Protein Data Bank (PDB) to locate proteins with a specific 3D arrangement of catalytic groups to identify active sites that might be redesigned to catalyze new reactions. As a proof-of-principle test, SABER was used to identify enzymes that have the same catalytic group arrangement present in o-succinyl benzoate synthase (OSBS). Among the highest-scoring scaffolds identified by the SABER search for enzymes with the same catalytic group arrangement as OSBS were l-Ala d/l-Glu epimerase (AEE) and muconate lactonizing enzyme II (MLE), both of which have been redesigned to become effective OSBS catalysts, demonstrated by experiments. Next, we used SABER to search for naturally existing active sites in the PDB with catalytic groups similar to those present in the designed Kemp elimination enzyme KE07. From over 2000 geometric matches to the KE07 active site, SABER identified 23 matches that corresponded to residues from known active sites. The best of these matches, with a 0.28 Å catalytic atom RMSD to KE07, was then redesigned to be compatible with the Kemp elimination using RosettaDesign. We also used SABER to search for potential Kemp eliminases using a theozyme predicted to provide a greater rate acceleration than the active site of KE07, and used Rosetta to create a design based on the proteins identified. PMID:22492397

Redox competition mode of scanning electrochemical microscopy (RC-SECM) for visualisation of local catalytic activity.

PubMed

Eckhard, Kathrin; Chen, Xingxing; Turcu, Florin; Schuhmann, Wolfgang

2006-12-07

In order to locally analyse catalytic activity on modified surfaces a transient redox competition mode of scanning electrochemical microscopy (SECM) has been developed. In a bi-potentiostatic experiment the SECM tip competes with the sample for the very same analyte. This leads to a current decrease at the SECM tip, if it is positioned in close proximity to an active catalyst site on the surface. Specifically, local catalytic activity of a Pt-catalyst modified sample with respect to the catalytic reduction of molecular oxygen was investigated. At higher local catalytic activity the local 02 partial pressure within the gap between accurately positioned SECM tip and sample is depleted, leading to a noticeable tip current decrease over active sites. A flexible software module has been implemented into the SECM to adapt the competition conditions by proper definition of tip and sample potentials. A potential pulse profile enables the localised electrochemically induced generation of molecular oxygen prior to the competition detection. The current decay curves are recorded over the entire duration of the applied reduction pulse. Hence, a time resolved processing of the acquired current values provides movies of the local oxygen concentration against x,y-position. The SECM redox competition mode was verified with a macroscopic Pt-disk electrode as a test sample to demonstrate the feasibility of the approach. Moreover, highly dispersed electro-deposited spots of gold and platinum on glassy carbon were visualised using the redox competition mode of SECM. Catalyst spots of different nature as well as activity inhomogeneities within one spot caused by local variations in Pt-loading were visualised successfully.

Probing the Catalytic Mechanism of Vibrio harveyi GH20 β-N-Acetylglucosaminidase by Chemical Rescue

PubMed Central

Meekrathok, Piyanat; Suginta, Wipa

2016-01-01

Background Vibrio harveyi GH20 β-N-acetylglucosaminidase (VhGlcNAcase) is a chitinolytic enzyme responsible for the successive degradation of chitin fragments to GlcNAc monomers, activating the onset of the chitin catabolic cascade in marine Vibrios. Methods Two invariant acidic pairs (Asp303-Asp304 and Asp437-Glu438) of VhGlcNAcase were mutated using a site-directed mutagenesis strategy. The effects of these mutations were examined and the catalytic roles of these active-site residues were elucidated using a chemical rescue approach. Enhancement of the enzymic activity of the VhGlcNAcase mutants was evaluated by a colorimetric assay using pNP-GlcNAc as substrate. Results Substitution of Asp303, Asp304, Asp437 or Glu438 with Ala/Asn/Gln produced a dramatic loss of the GlcNAcase activity. However, the activity of the inactive D437A mutant was recovered in the presence of sodium formate. Our kinetic data suggest that formate ion plays a nucleophilic role by mimicking the β-COO-side chain of Asp437, thereby stabilizing the reaction intermediate during both the glycosylation and the deglycosylation steps. Conclusions Chemical rescue of the inactive D437A mutant of VhGlcNAcase by an added nucleophile helped to identify Asp437 as the catalytic nucleophile/base, and hence its acidic partner Glu438 as the catalytic proton donor/acceptor. General Significance Identification of the catalytic nucleophile of VhGlcNAcases supports the proposal of a substrate-assisted mechanism of GH20 GlcNAcases, requiring the catalytic pair Asp437-Glu438 for catalysis. The results suggest the mechanistic basis of the participation of β-N-acetylglucosaminidase in the chitin catabolic pathway of marine Vibrios. PMID:26870945

Engineering of Helicobacter pylori L-asparaginase: characterization of two functionally distinct groups of mutants.

PubMed

Maggi, Maristella; Chiarelli, Laurent R; Valentini, Giovanna; Scotti, Claudia

2015-01-01

Bacterial L-asparaginases have been used as anti-cancer drugs for over 4 decades though presenting, along with their therapeutic efficacy, several side effects due to their bacterial origin and, seemingly, to their secondary glutaminase activity. Helicobacter pylori type II L-asparaginase possesses interesting features, among which a reduced catalytic efficiency for L-GLN, compared to the drugs presently used in therapy. In the present study, we describe some enzyme variants with catalytic and in vitro cytotoxic activities different from the wild type enzyme. Particularly, replacements on catalytic threonines (T16D and T95E) deplete the enzyme of both its catalytic activities, once more underlining the essential role of such residues. One serendipitous mutant, M121C/T169M, had a preserved efficiency vs L-asparagine but was completely unable to carry out L-glutamine hydrolysis. Interestingly, this variant did not exert any cytotoxic effect on HL-60 cells. The M121C and T169M single mutants had reduced catalytic activities (nearly 2.5- to 4-fold vs wild type enzyme, respectively). Mutant Q63E, endowed with a similar catalytic efficiency versus asparagine and halved glutaminase efficiency with respect to the wild type enzyme, was able to exert a cytotoxic effect comparable to, or higher than, the one of the wild type enzyme when similar asparaginase units were used. These findings may be relevant to determine the role of glutaminase activity of L-asparaginase in the anti-proliferative effect of the drug and to shed light on how to engineer the best asparaginase/glutaminase combination for an ever improved, patients-tailored therapy.

Engineering of Helicobacter pylori L-Asparaginase: Characterization of Two Functionally Distinct Groups of Mutants

PubMed Central

Maggi, Maristella; Chiarelli, Laurent R.; Valentini, Giovanna; Scotti, Claudia

2015-01-01

Bacterial L-asparaginases have been used as anti-cancer drugs for over 4 decades though presenting, along with their therapeutic efficacy, several side effects due to their bacterial origin and, seemingly, to their secondary glutaminase activity. Helicobacter pylori type II L-asparaginase possesses interesting features, among which a reduced catalytic efficiency for L-GLN, compared to the drugs presently used in therapy. In the present study, we describe some enzyme variants with catalytic and in vitro cytotoxic activities different from the wild type enzyme. Particularly, replacements on catalytic threonines (T16D and T95E) deplete the enzyme of both its catalytic activities, once more underlining the essential role of such residues. One serendipitous mutant, M121C/T169M, had a preserved efficiency vs L-asparagine but was completely unable to carry out L-glutamine hydrolysis. Interestingly, this variant did not exert any cytotoxic effect on HL-60 cells. The M121C and T169M single mutants had reduced catalytic activities (nearly 2.5- to 4-fold vs wild type enzyme, respectively). Mutant Q63E, endowed with a similar catalytic efficiency versus asparagine and halved glutaminase efficiency with respect to the wild type enzyme, was able to exert a cytotoxic effect comparable to, or higher than, the one of the wild type enzyme when similar asparaginase units were used. These findings may be relevant to determine the role of glutaminase activity of L-asparaginase in the anti-proliferative effect of the drug and to shed light on how to engineer the best asparaginase/glutaminase combination for an ever improved, patients-tailored therapy. PMID:25664771

Investigation of the Origin of Catalytic Activity in Oxide-Supported Nanoparticle Gold

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrison, Ian

Since Haruta’s discovery in 1987 of the surprising catalytic activity of supported Au nanoparticles, we have seen a very large number of experimental and theoretical efforts to explain this activity and to fully understand the nature of the behavior of the responsible active sites. In 2011, we discovered that a dual catalytic site at the perimeter of ~3nm diameter Au particles supported on TiO 2 is responsible for oxidative catalytic activity. O 2 molecules bind with Au atoms and Ti4+ ions in the TiO 2 support and the weakened O-O bond dissociates at low temperatures, proceeding to produce O atomsmore » which act as oxidizing agents for the test molecule, CO. The papers supported by DOE have built on this finding and have been concerned with two aspects of the behavior of Au/TiO 2 catalysts: (1). Mechanistic behavior of dual catalytic sites in the oxidation of organic molecules such as ethylene and acetic acid; (2). Studies of the electronic properties of the TiO 2 (110) single crystal in relation to its participation in charge transfer at the occupied dual catalytic site. A total of 20 papers have been produced through DOE support of this work. The papers combine IR spectroscopic investigations of Au/TiO 2 catalysts with surface science on the TiO 2(110) and TiO 2 nanoparticle surfaces with modern density functional modeling. The primary goals of the work were to investigate the behavior of the dual Au/Ti 4+ site for the partial oxidation of alcohols to acids, the hydrogenation of aldehydes and ketones to alcohols, and the condensation of oxygenate intermediates- all processes related to the utilization of biomass in the production of useful chemical energy sources.« less

Role of κ→λ light-chain constant-domain switch in the structure and functionality of A17 reactibody

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ponomarenko, Natalia; Chatziefthimiou, Spyros D.; Kurkova, Inna

2014-03-01

Catalytic antibody variants with κ and λ light-chain constant domains show differences in their crystal structures which lead to subtle changes in catalytic efficiency and thermodynamic parameters as well as in their affinity for peptide substrates. The engineering of catalytic function in antibodies requires precise information on their structure. Here, results are presented that show how the antibody domain structure affects its functionality. The previously designed organophosphate-metabolizing reactibody A17 has been re-engineered by replacing its constant κ light chain by the λ chain (A17λ), and the X-ray structure of A17λ has been determined at 1.95 Å resolution. It was foundmore » that compared with A17κ the active centre of A17λ is displaced, stabilized and made more rigid owing to interdomain interactions involving the CDR loops from the V{sub L} and V{sub H} domains. These V{sub L}/V{sub H} domains also have lower mobility, as deduced from the atomic displacement parameters of the crystal structure. The antibody elbow angle is decreased to 126° compared with 138° in A17κ. These structural differences account for the subtle changes in catalytic efficiency and thermodynamic parameters determined with two organophosphate ligands, as well as in the affinity for peptide substrates selected from a combinatorial cyclic peptide library, between the A17κ and A17λ variants. The data presented will be of interest and relevance to researchers dealing with the design of antibodies with tailor-made functions.« less

Exploring the Reaction Pathways of Bioglycerol Hydrodeoxygenation to Propene over Molybdena-Based Catalysts.

PubMed

Zacharopoulou, Vasiliki; Vasiliadou, Efterpi S; Lemonidou, Angeliki A

2018-01-10

The one-step reaction of glycerol with hydrogen to form propene selectively is a particularly challenging catalytic pathway that has not yet been explored thoroughly. Molybdena-based catalysts are active and selective to C-O bond scission; propene is the only product in the gas phase under the standard reaction conditions, and further hydrogenation to propane is impeded. Within this context, this work focuses on the exploration of the reaction pathways and the investigation of various parameters that affect the catalytic performance, such as the role of hydrogen on the product distribution and the effect of the catalyst pretreatment step. Under a hydrogen atmosphere, propene is produced primarily via 2-propenol, whereas under an inert atmosphere propanal and glycerol dissociation products are formed mainly. The reaction most likely proceeds through a reverse Mars-van Krevelen mechanism as partially reduced Mo species drive the reaction to the formation of the desired product. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Two stages catalytic pyrolysis of refuse derived fuel: production of biofuel via syncrude.

PubMed

Miskolczi, N; Buyong, F; Angyal, A; Williams, P T; Bartha, L

2010-11-01

Thermo-catalytic pyrolysis of refuse derived fuels with different catalysts had been conducted in a two stages process due to its important potential value as fuel. The first stage was a pure thermal pyrolysis in a horizontal tubular reactor with feed rate of 0.5kg hourly. The second stage was a semi-batch process in the presence of catalysts. Results showed that the tested catalysts significantly have affected the quantity of products. E.g. gas yield could be increased with 350% related to the catalyst free case using ZSM-5, while that of pyrolytic oil was 115% over Y-zeolite. Gases consisted of mainly CO and CO(2) obtained from the tubular reactor, while dominantly hydrocarbons from the second stage. Ni-Mo-catalyst and Co-Mo-catalyst had shown activity in pyrolytic oil upgrading via in-situ hydrogenation-dehydrogenation reactions. Sulphur, nitrogen and chlorine level in pyrolytic oils could be significantly declined by using of catalysts.

Drosophila variable nurse cells encodes Arrest defective 1 (ARD1), the catalytic subunit of the major N-terminal acetyltransferase complex

PubMed Central

Wang, Ying; Mijares, Michelle; Gall, Megan D.; Turan, Tolga; Javier, Anna; Bornemann, Douglas J; Manage, Kevin; Warrior, Rahul

2010-01-01

Mutations in the Drosophila variable nurse cells (vnc) gene result in female sterility and oogenesis defects, including egg chambers with too many or too few nurse cells. We show that vnc corresponds to Arrest Defective1 (Ard1) and encodes the catalytic subunit of NatA, the major N-terminal acetyl-transferase complex. While N-terminal acetylation is one of the most prevalent covalent protein modifications in eukaryotes, analysis of its role in development has been challenging since mutants that compromise NatA activity have not been described in any multicellular animal. Our data show that reduced ARD1 levels result in pleiotropic oogenesis defects including abnormal cyst encapsulation, desynchronized cystocyte division, disrupted nurse cell chromosome dispersion and abnormal chorion patterning, consistent with the wide range of predicted NatA substrates. Further we find that loss of Ard1 affects cell survival/proliferation and is lethal for the animal, providing the first demonstration that this modification is essential in higher eukaryotes. PMID:20882681

Biodiesel production via the transesterification of soybean oil using waste starfish (Asterina pectinifera).

PubMed

Jo, Yong Beom; Park, Sung Hoon; Jeon, Jong-Ki; Ko, Chang Hyun; Ryu, Changkook; Park, Young-Kwon

2013-07-01

Calcined waste starfish was used as a base catalyst for the production of biodiesel from soybean oil for the first time. A batch reactor was used for the transesterification reaction. The thermal characteristics and crystal structures of the waste starfish were investigated by thermo-gravimetric analysis and X-ray diffraction. The biodiesel yield was determined by measuring the content of fatty acid methyl esters (FAME). The calcination temperature appeared to be a very important parameter affecting the catalytic activity. The starfish-derived catalyst calcined at 750 °C or higher exhibited high activity for the transesterification reaction. The FAME content increased with increasing catalyst dose and methanol-over-oil ratio.

In situ IR and X-ray high spatial-resolution microspectroscopy measurements of multistep organic transformation in flow microreactor catalyzed by Au nanoclusters.

PubMed

Gross, Elad; Shu, Xing-Zhong; Alayoglu, Selim; Bechtel, Hans A; Martin, Michael C; Toste, F Dean; Somorjai, Gabor A

2014-03-05

Analysis of catalytic organic transformations in flow reactors and detection of short-lived intermediates are essential for optimization of these complex reactions. In this study, spectral mapping of a multistep catalytic reaction in a flow microreactor was performed with a spatial resolution of 15 μm, employing micrometer-sized synchrotron-based IR and X-ray beams. Two nanometer sized Au nanoclusters were supported on mesoporous SiO2, packed in a flow microreactor, and activated toward the cascade reaction of pyran formation. High catalytic conversion and tunable products selectivity were achieved under continuous flow conditions. In situ synchrotron-sourced IR microspectroscopy detected the evolution of the reactant, vinyl ether, into the primary product, allenic aldehyde, which then catalytically transformed into acetal, the secondary product. By tuning the residence time of the reactants in a flow microreactor a detailed analysis of the reaction kinetics was performed. An in situ micrometer X-ray absorption spectroscopy scan along the flow reactor correlated locally enhanced catalytic conversion, as detected by IR microspectroscopy, to areas with high concentration of Au(III), the catalytically active species. These results demonstrate the fundamental understanding of the mechanism of catalytic reactions which can be achieved by the detailed mapping of organic transformations in flow reactors.

The physicochemical properties and catalytic performance of carbon-covered alumina for oxidative dehydrogenation of ethylbenzene with CO2

NASA Astrophysics Data System (ADS)

Wang, Tehua; Chong, Siying; Wang, Tongtong; Lu, Huiyi; Ji, Min

2018-01-01

In order to correlate the physicochemical properties of carbon-covered alumina (CCA) materials with their catalytic performance for oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB), a series of CCA materials with diverse carbon contents (8.7-31.3 wt%) and pyrolysis temperatures (600-800 °C), which were synthesized via an impregnation method followed by pyrolysis, were applied. These catalytic materials were characterized by TGA, N2 physisorption, XRD, Raman spectroscopy and XPS techniques. It was found that the catalytic performance of these CCA materials highly depended on their physicochemical properties, and the optimum CCA catalyst exhibited much better catalytic stability than conventional hydroxyl carbon nanotubes. Below an optimum value of carbon content, the CCA catalyst preserved the main pore characteristics of the Al2O3 support and its catalytic activity increased with the carbon content. Excessive carbon loading resulted in significant textural alterations and thereby decreased both the ethylbenzene conversion and styrene selectivity. On the other hand, high pyrolysis temperature was detrimental to the ordered graphitic structure of the carbon species within the Al2O3 pore. The decreased ordered graphitic degree was found to be associated with the loss of the surface active carbonyl groups, consequently hampering the catalytic efficiency of the CCA catalyst.

Development of a high-temperature durable catalyst for use in catalytic combustors for advanced automotive gas turbine engines

NASA Astrophysics Data System (ADS)

Tong, H.; Snow, G. C.; Chu, E. K.; Chang, R. L. S.; Angwin, M. J.; Pessagno, S. L.

1981-09-01

Durable catalytic reactors for advanced gas turbine engines were developed. Objectives were: to evaluate furnace aging as a cost effective catalytic reactor screening test, measure reactor degradation as a function of furnace aging, demonstrate 1,000 hours of combustion durability, and define a catalytic reactor system with a high probability of successful integration into an automotive gas turbine engine. Fourteen different catalytic reactor concepts were evaluated, leading to the selection of one for a durability combustion test with diesel fuel for combustion conditions. Eight additional catalytic reactors were evaluated and one of these was successfully combustion tested on propane fuel. This durability reactor used graded cell honeycombs and a combination of noble metal and metal oxide catalysts. The reactor was catalytically active and structurally sound at the end of the durability test.

Development of a high-temperature durable catalyst for use in catalytic combustors for advanced automotive gas turbine engines

NASA Technical Reports Server (NTRS)

Tong, H.; Snow, G. C.; Chu, E. K.; Chang, R. L. S.; Angwin, M. J.; Pessagno, S. L.

1981-01-01

Durable catalytic reactors for advanced gas turbine engines were developed. Objectives were: to evaluate furnace aging as a cost effective catalytic reactor screening test, measure reactor degradation as a function of furnace aging, demonstrate 1,000 hours of combustion durability, and define a catalytic reactor system with a high probability of successful integration into an automotive gas turbine engine. Fourteen different catalytic reactor concepts were evaluated, leading to the selection of one for a durability combustion test with diesel fuel for combustion conditions. Eight additional catalytic reactors were evaluated and one of these was successfully combustion tested on propane fuel. This durability reactor used graded cell honeycombs and a combination of noble metal and metal oxide catalysts. The reactor was catalytically active and structurally sound at the end of the durability test.

Mechanism and Catalytic Site Atlas (M-CSA): a database of enzyme reaction mechanisms and active sites.

PubMed

Ribeiro, António J M; Holliday, Gemma L; Furnham, Nicholas; Tyzack, Jonathan D; Ferris, Katherine; Thornton, Janet M

2018-01-04

M-CSA (Mechanism and Catalytic Site Atlas) is a database of enzyme active sites and reaction mechanisms that can be accessed at www.ebi.ac.uk/thornton-srv/m-csa. Our objectives with M-CSA are to provide an open data resource for the community to browse known enzyme reaction mechanisms and catalytic sites, and to use the dataset to understand enzyme function and evolution. M-CSA results from the merging of two existing databases, MACiE (Mechanism, Annotation and Classification in Enzymes), a database of enzyme mechanisms, and CSA (Catalytic Site Atlas), a database of catalytic sites of enzymes. We are releasing M-CSA as a new website and underlying database architecture. At the moment, M-CSA contains 961 entries, 423 of these with detailed mechanism information, and 538 with information on the catalytic site residues only. In total, these cover 81% (195/241) of third level EC numbers with a PDB structure, and 30% (840/2793) of fourth level EC numbers with a PDB structure, out of 6028 in total. By searching for close homologues, we are able to extend M-CSA coverage of PDB and UniProtKB to 51 993 structures and to over five million sequences, respectively, of which about 40% and 30% have a conserved active site. © The Author(s) 2017. Published by Oxford University Press on behalf of Nucleic Acids Research.

Atomic-Scale Principles of Combustion Nanocatalysis

DTIC Science & Technology

2014-05-19

of Combustion Nanocatalysts: Structures, Electronic Characteristics and Catalytic Pathways MURI FINAL REPORT Reporting Period: June 1, 2008 to...properties of nanoscale materials to be employed for catalytic combustion of fuels and propellants. Furthermore the research program seeks to establish... catalytic cycle. Both the carbon– hydrogen bond activation and the subsequent desorption of the ethylene product molecule require cooperative action

Effects of protonation state of Asp181 and position of active site water molecules on the conformation of PTP1B.

PubMed

Ozcan, Ahmet; Olmez, Elif Ozkirimli; Alakent, Burak

2013-05-01

In protein tyrosine phosphatase 1B (PTP1B), the flexible WPD loop adopts a closed conformation (WPDclosed ) in the active state of PTP1B, bringing the catalytic Asp181 close to the active site pocket, while WPD loop is in an open conformation (WPDopen ) in the inactive state. Previous studies showed that Asp181 may be protonated at physiological pH, and ordered water molecules exist in the active site. In the current study, molecular dynamics simulations are employed at different Asp181 protonation states and initial positions of active site water molecules, and compared with the existing crystallographic data of PTP1B. In WPDclosed conformation, the active site is found to maintain its conformation only in the protonated state of Asp181 in both free and liganded states, while Asp181 is likely to be deprotonated in WPDopen conformation. When the active site water molecule network that is a part of the free WPDclosed crystal structure is disrupted, intermediate WPD loop conformations, similar to that in the PTPRR crystal structure, are sampled in the MD simulations. In liganded PTP1B, one active site water molecule is found to be important for facilitating the orientation of Cys215 and the phosphate ion, thus may play a role in the reaction. In conclusion, conformational stability of WPD loop, and possibly catalytic activity of PTP1B, is significantly affected by the protonation state of Asp181 and position of active site water molecules, showing that these aspects should be taken into consideration both in MD simulations and inhibitor design. Copyright © 2013 Wiley Periodicals, Inc.

The Design, Synthesis, and Characterization of Open Sites on Metal Clusters

NASA Astrophysics Data System (ADS)

Nigra, Michael Mark

Coordinatively unsaturated corner and edge atoms have been hypothesized to have the highest activity of sites responsible for many catalytic reactions on a metal surface. Recent studies have validated this hypothesis in varied reaction systems. However, quantification of different types of coordinatively unsaturated sites, and elucidation of their individual catalytic rates has remained a largely unresolved challenge when understanding catalysis on metal surfaces. Yet such structure-function knowledge would be invaluable to the design of more active and selective metal-surface catalysts in the future. I investigated the catalytic contributions of undercoordinated sites such as corner and edge atoms are investigated in a model reaction system using organic ligands bound to the gold nanoparticle surface. The catalyst consisted of 4 nm gold nanoparticles on a metal oxide support, using resazurin to resorufin as a model reaction system. My results demonstrate that in this system, corner atom sites are the most undercoordinated sites, and are over an order of magnitude more active when compared to undercoordinated edge atom sites, while terrace sites remain catalytically inactive for the reduction reaction of resazurin to resorufin. Catalytic activity has been also demonstrated for calixarene-bound gold nanoparticles using the reduction of 4-nitrophenol. With the 4-nitrophenol reduction reaction, a comparative study was undertaken to compare calixarene phosphine and calixarene thiol bound 4 nm gold particles. The results of the study suggested that a leached site was responsible for catalysis and not sites on the original gold nanoparticles. Future experiments with calixarene bound gold clusters could investigate ligand effects in reactions where the active site is not a leached or aggregated gold species, possibly in oxidation reactions, where electron-rich gold is hypothesized to be a good catalyst. The results that emphasize the enhanced catalytic activity of undercoordinated sites led me to synthesize small gold clusters consisting of a high fraction of coordinatively unsaturated open sites. This was enabled through an approach that utilized bulky calix[4]arene ligands that are bound to a gold core. Since the size of the calix[4]arene ligand is commensurate with the size of the gold cluster core, the calix[4]arene ligand does not pack closely together on the gold cluster surface. This in turn results in areas of accessible gold atom sites between ligands. Additionally, these calix[4]arene ligands prevent cluster aggregation and electronically tune the gold core in a manner conceptually similar to enzymes affecting reactivity through organic side-chains acting as ligands. I quantified the number of open sites that result from this packing problem on the gold cluster surface, using fluorescence probe chemisorption experiments. The results of these chemisorption measurements support the mechanical model of accessibility whereby accessibility is not dependent on the identity of the functional group, whether it be calixarene phosphines or N-heterocyclic carbenes, bound to the gold surface, but rather to the relative radii of curvature of bound ligands and the gold cluster core. Additional materials characterization was completed with transmission electron microscopy in both bright-field imaging of zeolites, in MCM-22 and delaminated ITQ-2 and UCB-1 materials, and in dark field imaging of glucan coatings on oxide particles. These materials could prove to be interesting materials as to use as supports for the calixarene-bound metal clusters described above or for other metal clusters.

Metal active site elasticity linked to activation of homocysteine in methionine synthases

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koutmos, Markos; Pejchal, Robert; Bomer, Theresa M.

2008-04-02

Enzymes possessing catalytic zinc centers perform a variety of fundamental processes in nature, including methyl transfer to thiols. Cobalamin-independent (MetE) and cobalamin-dependent (MetH) methionine synthases are two such enzyme families. Although they perform the same net reaction, transfer of a methyl group from methyltetrahydrofolate to homocysteine (Hcy) to form methionine, they display markedly different catalytic strategies, modular organization, and active site zinc centers. Here we report crystal structures of zinc-replete MetE and MetH, both in the presence and absence of Hcy. Structural investigation of the catalytic zinc sites of these two methyltransferases reveals an unexpected inversion of zinc geometry uponmore » binding of Hcy and displacement of an endogenous ligand in both enzymes. In both cases a significant movement of the zinc relative to the protein scaffold accompanies inversion. These structures provide new information on the activation of thiols by zinc-containing enzymes and have led us to propose a paradigm for the mechanism of action of the catalytic zinc sites in these and related methyltransferases. Specifically, zinc is mobile in the active sites of MetE and MetH, and its dynamic nature helps facilitate the active site conformational changes necessary for thiol activation and methyl transfer.« less

Synthesis of urease hybrid nanoflowers and their enhanced catalytic properties.

PubMed

Somturk, Burcu; Yilmaz, Ismail; Altinkaynak, Cevahir; Karatepe, Aslıhan; Özdemir, Nalan; Ocsoy, Ismail

2016-05-01

Increasing numbers of materials have been extensively used as platforms for enzyme immobilization to enhance catalytic activity and stability. Although stability of enzyme was accomplished with immobilization approaches, activity of the most of the enzymes was declined after immobilization. Herein, we synthesize the flower shaped-hybrid nanomaterials called hybrid nanoflower (HNF) consisting of urease enzyme and copper ions (Cu(2+)) and report a mechanistic elucidation of enhancement in both activity and stability of the HNF. We demonstrated how experimental factors influence morphology of the HNF. We proved that the HNF (synthesized from 0.02mgmL(-1) urease in 10mM PBS (pH 7.4) at +4°C) exhibited the highest catalytic activity of ∼2000% and ∼4000% when stored at +4°C and RT, respectively compared to free urease. The highest stability was also achieved by this HNF by maintaining 96.3% and 90.28% of its initial activity within storage of 30 days at +4°C and RT, respectively. This dramatically enhanced activity is attributed to high surface area, nanoscale-entrapped urease and favorable urease conformation of the HNF. The exceptional catalytic activity and stability properties of HNF can be taken advantage of to use it in fields of biomedicine and chemistry. Copyright © 2015 Elsevier Inc. All rights reserved.

Facile solid-state synthesis of highly dispersed Cu nanospheres anchored on coal-based activated carbons as an efficient heterogeneous catalyst for the reduction of 4-nitrophenol

NASA Astrophysics Data System (ADS)

Wang, Shan; Gao, Shasha; Tang, Yakun; Wang, Lei; Jia, Dianzeng; Liu, Lang

2018-04-01

Coal-based activated carbons (AC) were acted as the support, Cu/AC catalysts were synthesized by a facile solid-state reaction combined with subsequent heat treatment. In Cu/AC composites, highly dispersed Cu nanospheres were anchored on AC. The catalytic activity for 4-nitrophenol (4-NP) was investigated, the effects of activation temperature and copper loading on the catalytic performance were studied. The catalysts exhibited very high catalytic activity and moderate chemical stability due to the unique characteristics of the particle-assembled nanostructures, the high surface area and the porous structure of coal-based AC and the good dispersion of metal particles. Design and preparation of non-noble metal composite catalysts provide a new direction for improving the added value of coal.

Catalytic activity of platinum on ruthenium electrodes with modified (electro)chemical states.

PubMed

Park, Kyung-Won; Sung, Yung-Eun

2005-07-21

Using Pt on Ru thin-film electrodes with various (electro)chemical states designed by the sputtering method, the effect of Ru states on the catalytic activity of Pt was investigated. The chemical and electrochemical properties of Pt/Ru thin-film samples were confirmed by X-ray photoelectron spectroscopy (XPS) and cyclic voltammetry. In addition, Pt nanoparticles on Ru metal or oxide for an actual fuel cell system showed an effect of Ru states on the catalytic activity of Pt in methanol electrooxidation. Finally, it was concluded that such an enhancement of methanol electrooxidation on the Pt is responsible for Ru metallic and/or oxidation sites compared to pure Pt without any Ru state.

Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling

PubMed Central

2012-01-01

Background The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst. Results It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4′-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4′-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1. Conclusions Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst. PMID:22947394

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

NASA Astrophysics Data System (ADS)

Forbes, Lauren Marie

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

Immobilization of Acetobacter sp. CCTCC M209061 for efficient asymmetric reduction of ketones and biocatalyst recycling.

PubMed

Chen, Xiao-Hong; Wang, Xiao-Ting; Lou, Wen-Yong; Li, Ying; Wu, Hong; Zong, Min-Hua; Smith, Thomas J; Chen, Xin-De

2012-09-04

The bacterium Acetobacter sp. CCTCC M209061 is a promising whole-cell biocatalyst with exclusive anti-Prelog stereoselectivity for the reduction of prochiral ketones that can be used to make valuable chiral alcohols such as (R)-4-(trimethylsilyl)-3-butyn-2-ol. Although it has promising catalytic properties, its stability and reusability are relatively poor compared to other biocatalysts. Hence, we explored various materials for immobilizing the active cells, in order to improve the operational stability of biocatalyst. It was found that Ca-alginate give the best immobilized biocatalyst, which was then coated with chitosan to further improve its mechanical strength and swelling-resistance properties. Conditions were optimized for formation of reusable immobilized beads which can be used for repeated batch asymmetric reduction of 4'-chloroacetophenone. The optimized immobilized biocatalyst was very promising, with a specific activity of 85% that of the free-cell biocatalyst (34.66 μmol/min/g dw of cells for immobilized catalyst vs 40.54 μmol/min/g for free cells in the asymmetric reduction of 4'-chloroacetophenone). The immobilized cells showed better thermal stability, pH stability, solvent tolerance and storability compared with free cells. After 25 cycles reaction, the immobilized beads still retained >50% catalytic activity, which was 3.5 times higher than degree of retention of activity by free cells reused in a similar way. The cells could be recultured in the beads to regain full activity and perform a further 25 cycles of the reduction reaction. The external mass transfer resistances were negligible as deduced from Damkohler modulus Da < <1, and internal mass transfer restriction affected the reduction action but was not the principal rate-controlling step according to effectiveness factors η < 1 and Thiele modulus 0.3<∅ <1. Ca-alginate coated with chitosan is a highly effective material for immobilization of Acetobacter sp. CCTCC M209061 cells for repeated use in the asymmetric reduction of ketones. Only a small cost in terms of the slightly lower catalytic activity compared to free cells could give highly practicable immobilized biocatalyst.

Techno-economic and uncertainty analysis of in situ and ex situ fast pyrolysis for biofuel production.

PubMed

Li, Boyan; Ou, Longwen; Dang, Qi; Meyer, Pimphan; Jones, Susanne; Brown, Robert; Wright, Mark

2015-11-01

This study evaluates the techno-economic uncertainty in cost estimates for two emerging technologies for biofuel production: in situ and ex situ catalytic pyrolysis. The probability distributions for the minimum fuel-selling price (MFSP) indicate that in situ catalytic pyrolysis has an expected MFSP of $1.11 per liter with a standard deviation of 0.29, while the ex situ catalytic pyrolysis has a similar MFSP with a smaller deviation ($1.13 per liter and 0.21 respectively). These results suggest that a biorefinery based on ex situ catalytic pyrolysis could have a lower techno-economic uncertainty than in situ pyrolysis compensating for a slightly higher MFSP cost estimate. Analysis of how each parameter affects the NPV indicates that internal rate of return, feedstock price, total project investment, electricity price, biochar yield and bio-oil yield are parameters which have substantial impact on the MFSP for both in situ and ex situ catalytic pyrolysis. Copyright © 2015 Elsevier Ltd. All rights reserved.

Solution structure of the catalytic domain of RICH protein from goldfish.

PubMed

Kozlov, Guennadi; Denisov, Alexey Y; Pomerantseva, Ekaterina; Gravel, Michel; Braun, Peter E; Gehring, Kalle

2007-03-01

Regeneration-induced CNPase homolog (RICH) is an axonal growth-associated protein, which is induced in teleost fish upon optical nerve injury. RICH consists of a highly acidic N-terminal domain, a catalytic domain with 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity and a C-terminal isoprenylation site. In vitro RICH and mammalian brain CNPase specifically catalyze the hydrolysis of 2',3'-cyclic nucleotides to produce 2'-nucleotides, but the physiologically relevant in vivo substrate remains unknown. Here, we report the NMR structure of the catalytic domain of goldfish RICH and describe its binding to CNPase inhibitors. The structure consists of a twisted nine-stranded antiparallel beta-sheet surrounded by alpha-helices on both sides. Despite significant local differences mostly arising from a seven-residue insert in the RICH sequence, the active site region is highly similar to that of human CNPase. Likewise, refinement of the catalytic domain of rat CNPase using residual dipolar couplings gave improved agreement with the published crystal structure. NMR titrations of RICH with inhibitors point to a similar catalytic mechanism for RICH and CNPase. The results suggest a functional importance for the evolutionarily conserved phosphodiesterase activity and hint of a link with pre-tRNA splicing.

A novel 3D Ag(I)-MOF: Surfactant-directed syntheses and catalytic degradation of o/m/p-Nitrophenol

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Xue-Qian; Wen, Guo-Xuan; Wu, Ya-Pan

2016-10-15

For the first time, sodium caprylate has been investigated to direct the crystal growth of 3D Ag-MOF, [Ag{sub 2}(ddcba)(4,4′-bipy){sub 2}] (1), constructing from 3,5-(di(2′,5′-dicarboxylphenyl)benozoic acid and 4,4′-bipy. The single crystal diffraction analyses shows that complex 1 possess 3D neutral framework with a three-connected ThSi{sub 2} (10{sup 3}-b) topology. Compound 1 exhibits predominant catalytic activity towards the degradation of o-Nitrophenol (ONP), m-Nitrophenol (MNP) and p-Nitrophenol (PNP) in aqueous solution. The kinetics of such catalytic degradation reactions was also studied. - Graphical abstract: A novel 3D Ag(I)-MOF with ThSi{sub 2} (10{sup 3}-b) topology exhibits predominant catalytic activity towards the degradation of o-Nitrophenolmore » (ONP), m-Nitrophenol (MNP) and p-Nitrophenol (PNP) in aqueous solution. - Highlights: • A novel 3D Ag(I)-MOF with ThSi{sub 2} (10{sup 3}-b) topology. • Surfactant as additive for directing the crystal growth. • Predominant catalytic activities for the degradation of o/m/p-nitrophenol.« less

Catalytic Oxidation of Hydroquinone in Aqueous Solution over Bimetallic PdCo Catalyst Supported on Carbon: Effect of Interferents and Electrochemical Measurement.

PubMed

Ye, Weichun; Shi, Xuezhao; Zhang, Yane; Hong, Chenghui; Wang, Chunming; Budzianowski, Wojciech M; Xue, Desheng

2016-02-10

Palladium-cobalt alloy nanoparticles were synthesized and dispersed on carbon black support, aiming to have a less expensive catalyst. Catalytic behaviors of PdCo/C catalyst for the oxidation of hydroquinone (HQ) with H2O2 in aqueous solution were evaluated using high-performance liquid chromatography (HPLC). The results revealed that PdCo/C catalyst had better catalytic activity than an equal amount of commercial Pd/C and Co/C catalysts because of the d-band hybridization between Pd and Co. The effects of pH value, solvent, and various interferents including inorganic and organic compounds on the efficiency of HQ oxidation were further investigated. Furthermore, on the basis of mixed potential theory, comprehensive electrochemical measurements such as the open-circuit potential-time (OCP-t) technique and Tafel plot were efficient to assess the catalytic activity of the catalyst, and the results obtained were consistent with those of HPLC measurements. The efficient HQ oxidation was closely associated with the catalytic activity of PdCo nanoparticles because they accelerated the electron-transfer process and facilitated the generation of OH radicals.

An evolutionary analysis identifies a conserved pentapeptide stretch containing the two essential lysine residues for rice L-myo-inositol 1-phosphate synthase catalytic activity

PubMed Central

Basak, Papri; Maitra-Majee, Susmita; Das, Jayanta Kumar; Mukherjee, Abhishek; Ghosh Dastidar, Shubhra; Pal Choudhury, Pabitra

2017-01-01

A molecular evolutionary analysis of a well conserved protein helps to determine the essential amino acids in the core catalytic region. Based on the chemical properties of amino acid residues, phylogenetic analysis of a total of 172 homologous sequences of a highly conserved enzyme, L-myo-inositol 1-phosphate synthase or MIPS from evolutionarily diverse organisms was performed. This study revealed the presence of six phylogenetically conserved blocks, out of which four embrace the catalytic core of the functional protein. Further, specific amino acid modifications targeting the lysine residues, known to be important for MIPS catalysis, were performed at the catalytic site of a MIPS from monocotyledonous model plant, Oryza sativa (OsMIPS1). Following this study, OsMIPS mutants with deletion or replacement of lysine residues in the conserved blocks were made. Based on the enzyme kinetics performed on the deletion/replacement mutants, phylogenetic and structural comparison with the already established crystal structures from non-plant sources, an evolutionarily conserved peptide stretch was identified at the active pocket which contains the two most important lysine residues essential for catalytic activity. PMID:28950028

In-situ and self-distributed: A new understanding on catalyzed thermal decomposition process of ammonium perchlorate over Nd{sub 2}O{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zou, Min, E-mail: zoumin3362765@163.com; Wang, Xin, E-mail: wangx@mail.njust.edu.cn; Jiang, Xiaohong, E-mail: jxh0668@sina.com

2014-05-01

Catalyzed thermal decomposition process of ammonium perchlorate (AP) over neodymium oxide (Nd{sub 2}O{sub 3}) was investigated. Catalytic performances of nanometer-sized Nd{sub 2}O{sub 3} and micrometer-sized Nd{sub 2}O{sub 3} were evaluated by differential scanning calorimetry (DSC). In contrast to universal concepts, catalysts in different sizes have nearly similar catalytic activities. Based on structural and morphological variation of the catalysts during the reaction, combined with mass spectrum analyses and studies of unmixed style, a new understanding of this catalytic process was proposed. We believed that the newly formed chloride neodymium oxide (NdOCl) was the real catalytic species in the overall thermal decompositionmore » of AP over Nd{sub 2}O{sub 3}. Meanwhile, it was the “self-distributed” procedure which occurred within the reaction that also worked for the improvement of overall catalytic activities. This work is of great value in understanding the roles of micrometer-sized catalysts used in heterogeneous reactions, especially the solid–solid reactions which could generate a large quantity of gaseous species. - Graphical abstract: In-situ and self-distributed reaction process in thermal decomposition of AP catalyzed by Nd{sub 2}O{sub 3}. - Highlights: • Micro- and nano-Nd{sub 2}O{sub 3} for catalytic thermal decomposition of AP. • No essential differences on their catalytic performances. • Structural and morphological variation of catalysts digs out catalytic mechanism. • This catalytic process is “in-situ and self-distributed” one.« less

An Iron Reservoir to the Catalytic Metal

PubMed Central

Liu, Fange; Geng, Jiafeng; Gumpper, Ryan H.; Barman, Arghya; Davis, Ian; Ozarowski, Andrew; Hamelberg, Donald; Liu, Aimin

2015-01-01

The rubredoxin motif is present in over 74,000 protein sequences and 2,000 structures, but few have known functions. A secondary, non-catalytic, rubredoxin-like iron site is conserved in 3-hydroxyanthranilate 3,4-dioxygenase (HAO), from single cellular sources but not multicellular sources. Through the population of the two metal binding sites with various metals in bacterial HAO, the structural and functional relationship of the rubredoxin-like site was investigated using kinetic, spectroscopic, crystallographic, and computational approaches. It is shown that the first metal presented preferentially binds to the catalytic site rather than the rubredoxin-like site, which selectively binds iron when the catalytic site is occupied. Furthermore, an iron ion bound to the rubredoxin-like site is readily delivered to an empty catalytic site of metal-free HAO via an intermolecular transfer mechanism. Through the use of metal analysis and catalytic activity measurements, we show that a downstream metabolic intermediate can selectively remove the catalytic iron. As the prokaryotic HAO is often crucial for cell survival, there is a need for ensuring its activity. These results suggest that the rubredoxin-like site is a possible auxiliary iron source to the catalytic center when it is lost during catalysis in a pathway with metabolic intermediates of metal-chelating properties. A spare tire concept is proposed based on this biochemical study, and this concept opens up a potentially new functional paradigm for iron-sulfur centers in iron-dependent enzymes as transient iron binding and shuttling sites to ensure full metal loading of the catalytic site. PMID:25918158

AMP-Activated Protein Kinase Interacts with the Peroxisome Proliferator-Activated Receptor Delta to Induce Genes Affecting Fatty Acid Oxidation in Human Macrophages.

PubMed

Kemmerer, Marina; Finkernagel, Florian; Cavalcante, Marcela Frota; Abdalla, Dulcineia Saes Parra; Müller, Rolf; Brüne, Bernhard; Namgaladze, Dmitry

2015-01-01

AMP-activated protein kinase (AMPK) maintains energy homeostasis by suppressing cellular ATP-consuming processes and activating catabolic, ATP-producing pathways such as fatty acid oxidation (FAO). The transcription factor peroxisome proliferator-activated receptor δ (PPARδ) also affects fatty acid metabolism, stimulating the expression of genes involved in FAO. To question the interplay of AMPK and PPARδ in human macrophages we transduced primary human macrophages with lentiviral particles encoding for the constitutively active AMPKα1 catalytic subunit, followed by microarray expression analysis after treatment with the PPARδ agonist GW501516. Microarray analysis showed that co-activation of AMPK and PPARδ increased expression of FAO genes, which were validated by quantitative PCR. Induction of these FAO-associated genes was also observed upon infecting macrophages with an adenovirus coding for AMPKγ1 regulatory subunit carrying an activating R70Q mutation. The pharmacological AMPK activator A-769662 increased expression of several FAO genes in a PPARδ- and AMPK-dependent manner. Although GW501516 significantly increased FAO and reduced the triglyceride amount in very low density lipoproteins (VLDL)-loaded foam cells, AMPK activation failed to potentiate this effect, suggesting that increased expression of fatty acid catabolic genes alone may be not sufficient to prevent macrophage lipid overload.

AMP-Activated Protein Kinase Interacts with the Peroxisome Proliferator-Activated Receptor Delta to Induce Genes Affecting Fatty Acid Oxidation in Human Macrophages

PubMed Central

Kemmerer, Marina; Finkernagel, Florian; Cavalcante, Marcela Frota; Abdalla, Dulcineia Saes Parra; Müller, Rolf; Brüne, Bernhard; Namgaladze, Dmitry

2015-01-01

AMP-activated protein kinase (AMPK) maintains energy homeostasis by suppressing cellular ATP-consuming processes and activating catabolic, ATP-producing pathways such as fatty acid oxidation (FAO). The transcription factor peroxisome proliferator-activated receptor δ (PPARδ) also affects fatty acid metabolism, stimulating the expression of genes involved in FAO. To question the interplay of AMPK and PPARδ in human macrophages we transduced primary human macrophages with lentiviral particles encoding for the constitutively active AMPKα1 catalytic subunit, followed by microarray expression analysis after treatment with the PPARδ agonist GW501516. Microarray analysis showed that co-activation of AMPK and PPARδ increased expression of FAO genes, which were validated by quantitative PCR. Induction of these FAO-associated genes was also observed upon infecting macrophages with an adenovirus coding for AMPKγ1 regulatory subunit carrying an activating R70Q mutation. The pharmacological AMPK activator A-769662 increased expression of several FAO genes in a PPARδ- and AMPK-dependent manner. Although GW501516 significantly increased FAO and reduced the triglyceride amount in very low density lipoproteins (VLDL)-loaded foam cells, AMPK activation failed to potentiate this effect, suggesting that increased expression of fatty acid catabolic genes alone may be not sufficient to prevent macrophage lipid overload. PMID:26098914

Self-catalytic growth of unmodified gold nanoparticles as conductive bridges mediated gap-electrical signal transduction for DNA hybridization detection.

PubMed

Zhang, Jing; Nie, Huagui; Wu, Zhan; Yang, Zhi; Zhang, Lijie; Xu, Xiangju; Huang, Shaoming

2014-01-21

A simple and sensitive gap-electrical biosensor based on self-catalytic growth of unmodified gold nanoparticles (AuNPs) as conductive bridges has been developed for amplifying DNA hybridization events. In this strategy, the signal amplification degree of such conductive bridges is closely related to the variation of the glucose oxidase (GOx)-like catalytic activity of AuNPs upon interaction with single- and double-stranded DNA (ssDNA and dsDNA), respectively. In the presence of target DNA, the obtained dsDNA product cannot adsorb onto the surface of AuNPs due to electrostatic interaction, which makes the unmodified AuNPs exhibit excellent GOx-like catalytic activity. Such catalytic activity can enlarge the diameters of AuNPs in the glucose and HAuCl4 solution and result in a connection between most of the AuNPs and a conductive gold film formation with a dramatically increased conductance. For the control sample, the catalytic activity sites of AuNPs are fully blocked by ssDNA due to the noncovalent interaction between nucleotide bases and AuNPs. Thus, the growth of the assembled AuNPs will not happen and the conductance between microelectrodes will be not changed. Under the optimal experimental conditions, the developed strategy exhibited a sensitive response to target DNA with a high signal-to-noise ratio. Moreover, this strategy was also demonstrated to provide excellent differentiation ability for single-nucleotide polymorphism. Such performances indicated the great potential of this label-free electrical strategy for clinical diagnostics and genetic analysis under real biological sample separation.

Preparation of raspberry-like γ-Fe2O3/crackled nitrogen-doped carbon capsules and their application as supports to improve catalytic activity.

PubMed

Zhang, Junshuai; Yao, Tongjie; Zhang, Hui; Zhang, Xiao; Wu, Jie

2016-11-10

In this manuscript, we have introduced a novel method to improve the catalytic activity of metal nanoparticles via optimizing the support structure. To this end, raspberry-like γ-Fe 2 O 3 /crackled nitrogen-doped carbon (CNC) capsules were prepared by a two-step method. Compared with traditional magnetic capsules, in γ-Fe 2 O 3 /CNC capsules, the γ-Fe 2 O 3 nanoparticles were embedded in a CNC shell; therefore, they neither occupied the anchoring sites for metal nanoparticles nor came into contact with them, which was beneficial for increasing the metal nanoparticle loading. Numerous tiny cracks appeared on the porous CNC shell, which effectively improved the mass diffusion and transport in catalytic reactions. Additionally, the coordination interaction could be generated between the precursor metal ions and doped-nitrogen atoms in the capsule shell. With the help of these structural merits, γ-Fe 2 O 3 /CNC capsules were ideal supports for Pd nanoparticles, because they were beneficial for improving the Pd loading, reducing the nanoparticle size, increasing their dispersity and maximizing the catalytic performance of Pd nanoparticles anchored on the inner shell surface. As expected, γ-Fe 2 O 3 /CNC@Pd catalysts exhibited a dramatically enhanced catalytic activity towards hydrophilic 4-nitrophenol and hydrophobic nitrobenzene. The reaction rate constant k was compared with recent work and the corresponding reference samples. Moreover, they could be easily recycled by using a magnet and reused without an obvious loss of catalytic activity.

Ozone-Activated Nanoporous Gold: A Stable and Storable Material for Catalytic Oxidation

DOE PAGES

Personick, Michelle L.; Zugic, Branko; Biener, Monika M.; ...

2015-05-28

We report a new method for facile and reproducible activation of nanoporous gold (npAu) materials of different forms for the catalytic selective partial oxidation of alcohols under ambient pressure, steady flow conditions. This method, based on the surface cleaning of npAu ingots with ozone to remove carbon documented in ultrahigh vacuum conditions, produces active npAu catalysts from ingots, foils, and shells by flowing an ozone/dioxygen mixture over the catalyst at 150 °C, followed by a temperature ramp from 50 to 150 °C in a flowing stream of 10% methanol and 20% oxygen. With this treatment, all three materials (ingots, foils,more » and shells) can be reproducibly activated, despite potential carbonaceous poisons resulting from their synthesis, and are highly active for the selective oxidation of primary alcohols over prolonged periods of time. The npAu materials activated in this manner exhibit catalytic behavior substantially different from those activated under different conditions previously reported. Once activated in this manner, they can be stored and easily reactivated by flow of reactant gases at 150 °C for a few hours. They possess improved selectivity for the coupling of higher alcohols, such as 1-butanol, and are not active for carbon monoxide oxidation. As a result, this ozone-treated npAu is a functionally new catalytic material.« less

Ozone-Activated Nanoporous Gold: A Stable and Storable Material for Catalytic Oxidation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Personick, Michelle L.; Zugic, Branko; Biener, Monika M.

We report a new method for facile and reproducible activation of nanoporous gold (npAu) materials of different forms for the catalytic selective partial oxidation of alcohols under ambient pressure, steady flow conditions. This method, based on the surface cleaning of npAu ingots with ozone to remove carbon documented in ultrahigh vacuum conditions, produces active npAu catalysts from ingots, foils, and shells by flowing an ozone/dioxygen mixture over the catalyst at 150 °C, followed by a temperature ramp from 50 to 150 °C in a flowing stream of 10% methanol and 20% oxygen. With this treatment, all three materials (ingots, foils,more » and shells) can be reproducibly activated, despite potential carbonaceous poisons resulting from their synthesis, and are highly active for the selective oxidation of primary alcohols over prolonged periods of time. The npAu materials activated in this manner exhibit catalytic behavior substantially different from those activated under different conditions previously reported. Once activated in this manner, they can be stored and easily reactivated by flow of reactant gases at 150 °C for a few hours. They possess improved selectivity for the coupling of higher alcohols, such as 1-butanol, and are not active for carbon monoxide oxidation. As a result, this ozone-treated npAu is a functionally new catalytic material.« less

Conformational motions regulate phosphoryl transfer in related protein tyrosine phosphatases

PubMed Central

Whittier, Sean K.; Hengge, Alvan C.; Loria, J. Patrick

2014-01-01

Many studies have implicated a role for conformational motions during the catalytic cycle, acting to optimize the binding pocket or facilitate product release, but a more intimate role in the chemical reaction has not been described. We address this by monitoring active-site loop motion in two protein tyrosine phosphatases (PTPs) using NMR spectroscopy. The PTPs, YopH and PTP1B, have very different catalytic rates, however we find in both that the active-site loop closes to its catalytically competent position at rates that mirror the phosphotyrosine cleavage kinetics. This loop contains the catalytic acid, suggesting that loop closure occurs concomitantly with the protonation of the leaving group tyrosine and explains the different kinetics of two otherwise chemically and mechanistically indistinguishable enzymes. PMID:23970698

Use of an Improved Matching Algorithm to Select Scaffolds for Enzyme Design Based on a Complex Active Site Model.

PubMed

Huang, Xiaoqiang; Xue, Jing; Lin, Min; Zhu, Yushan

2016-01-01

Active site preorganization helps native enzymes electrostatically stabilize the transition state better than the ground state for their primary substrates and achieve significant rate enhancement. In this report, we hypothesize that a complex active site model for active site preorganization modeling should help to create preorganized active site design and afford higher starting activities towards target reactions. Our matching algorithm ProdaMatch was improved by invoking effective pruning strategies and the native active sites for ten scaffolds in a benchmark test set were reproduced. The root-mean squared deviations between the matched transition states and those in the crystal structures were < 1.0 Å for the ten scaffolds, and the repacking calculation results showed that 91% of the hydrogen bonds within the active sites are recovered, indicating that the active sites can be preorganized based on the predicted positions of transition states. The application of the complex active site model for de novo enzyme design was evaluated by scaffold selection using a classic catalytic triad motif for the hydrolysis of p-nitrophenyl acetate. Eighty scaffolds were identified from a scaffold library with 1,491 proteins and four scaffolds were native esterase. Furthermore, enzyme design for complicated substrates was investigated for the hydrolysis of cephalexin using scaffold selection based on two different catalytic motifs. Only three scaffolds were identified from the scaffold library by virtue of the classic catalytic triad-based motif. In contrast, 40 scaffolds were identified using a more flexible, but still preorganized catalytic motif, where one scaffold corresponded to the α-amino acid ester hydrolase that catalyzes the hydrolysis and synthesis of cephalexin. Thus, the complex active site modeling approach for de novo enzyme design with the aid of the improved ProdaMatch program is a promising approach for the creation of active sites with high catalytic efficiencies towards target reactions.

Use of an Improved Matching Algorithm to Select Scaffolds for Enzyme Design Based on a Complex Active Site Model

PubMed Central

Huang, Xiaoqiang; Xue, Jing; Lin, Min; Zhu, Yushan

2016-01-01

Active site preorganization helps native enzymes electrostatically stabilize the transition state better than the ground state for their primary substrates and achieve significant rate enhancement. In this report, we hypothesize that a complex active site model for active site preorganization modeling should help to create preorganized active site design and afford higher starting activities towards target reactions. Our matching algorithm ProdaMatch was improved by invoking effective pruning strategies and the native active sites for ten scaffolds in a benchmark test set were reproduced. The root-mean squared deviations between the matched transition states and those in the crystal structures were < 1.0 Å for the ten scaffolds, and the repacking calculation results showed that 91% of the hydrogen bonds within the active sites are recovered, indicating that the active sites can be preorganized based on the predicted positions of transition states. The application of the complex active site model for de novo enzyme design was evaluated by scaffold selection using a classic catalytic triad motif for the hydrolysis of p-nitrophenyl acetate. Eighty scaffolds were identified from a scaffold library with 1,491 proteins and four scaffolds were native esterase. Furthermore, enzyme design for complicated substrates was investigated for the hydrolysis of cephalexin using scaffold selection based on two different catalytic motifs. Only three scaffolds were identified from the scaffold library by virtue of the classic catalytic triad-based motif. In contrast, 40 scaffolds were identified using a more flexible, but still preorganized catalytic motif, where one scaffold corresponded to the α-amino acid ester hydrolase that catalyzes the hydrolysis and synthesis of cephalexin. Thus, the complex active site modeling approach for de novo enzyme design with the aid of the improved ProdaMatch program is a promising approach for the creation of active sites with high catalytic efficiencies towards target reactions. PMID:27243223

The influence of desilication on high-silica MFI and its catalytic performance for N2O decomposition

NASA Astrophysics Data System (ADS)

Shen, Qun; Wu, Minfang; Wang, Hui; Sun, Nannan; He, Chi; Wei, Wei

2018-05-01

A series of MFI zeolites with different Si/Al ratios were pretreated by a basic solution and their catalytic activity was evaluated in N2O decomposition after iron exchange. The performance of Fe-ZSM-5 catalysts could be improved by alkaline pretreatment. Among these samples, the activity curve of Fe-Z5-250-S sample could move to low temperature by >100 °C with a good preservation of hydrothermal stability. It is found that with the meso-microporous hybrid structure, the content of iron as active metal is significantly increased. Additionally, well preservation of the chemical environment around the tetrahedral aluminum and the site accessibility probably may be the other important factors to influence the catalytic activity.

Replacement of Val3 in human thymidylate synthase affects its kinetic properties and intracellular stability .

PubMed

Huang, Xiao; Gibson, Lydia M; Bell, Brittnaie J; Lovelace, Leslie L; Peña, Maria Marjorette O; Berger, Franklin G; Berger, Sondra H; Lebioda, Lukasz

2010-03-23

Human and other mammalian thymidylate synthase (TS) enzymes have an N-terminal extension of approximately 27 amino acids that is not present in bacterial TSs. The extension, which is disordered in all reported crystal structures of TSs, has been considered to play a primary role in protein turnover but not in catalytic activity. In mammalian cells, the variant V3A has a half-life similar to that of wild-type human TS (wt hTS) while V3T is much more stable; V3L, V3F, and V3Y have half-lives approximately half of that for wt hTS. Catalytic turnover rates for most Val3 mutants are only slightly diminished, as expected. However, two mutants, V3L and V3F, have strongly compromised dUMP binding, with K(m,app) values increased by factors of 47 and 58, respectively. For V3L, this observation can be explained by stabilization of the inactive conformation of the loop of residues 181-197, which prevents substrate binding. In the crystal structure of V3L, electron density corresponding to a leucine residue is present in a position that stabilizes the loop of residues 181-197 in the inactive conformation. Since this density is not observed in other mutants and all other leucine residues are ordered in this structure, it is likely that this density represents Leu3. In the crystal structure of a V3F.FdUMP binary complex, the nucleotide is bound in an alternative mode to that proposed for the catalytic complex, indicating that the high K(m,app) value is caused not by stabilization of the inactive conformer but by substrate binding in a nonproductive, inhibitory site. These observations show that the N-terminal extension affects the conformational state of the hTS catalytic region. Each of the mechanisms leading to the high K(m,app) values can be exploited to facilitate design of compounds acting as allosteric inhibitors of hTS.

Design and Preparation of Supported Au Catalyst with Enhanced Catalytic Activities by Rationally Positioning Au Nanoparticles on Anatase.

PubMed

Wang, Liang; Wang, Hong; Rice, Andrew E; Zhang, Wei; Li, Xiaokun; Chen, Mingshu; Meng, Xiangju; Lewis, James P; Xiao, Feng-Shou

2015-06-18

A synergistic effect between individual components is crucial for increasing the activity of metal/metal oxide catalysts. The greatest challenge is how to control the synergistic effect to obtain enhanced catalytic performance. Through density functional theory calculations of model Au/TiO2 catalysts, it is suggested that there is strong interaction between Au nanoparticles and Ti species at the edge/corner sites of anatase, which is favorable for the formation of stable oxygen vacancies. Motivated by this theoretical analysis, we have rationally prepared Au nanoparticles attached to edge/corner sites of anatase support (Au/TiO2-EC), confirmed by their HR-TEM images. As expected, this strong interaction is well characterized by Raman, UV-visible, and XPS techniques. Very interestingly, compared with conventional Au catalysts, Au/TiO2-EC exhibits superior catalytic activity in the oxidations using O2. Our approach to controlling Au nanoparticle positioning on anatase to obtain enhanced catalytic activity offers an efficient strategy for developing more novel supported metal catalysts.

Catalytic hydrolysis of ammonia borane via cobalt palladium nanoparticles.

PubMed

Sun, Daohua; Mazumder, Vismadeb; Metin, Önder; Sun, Shouheng

2011-08-23

Monodisperse 8 nm CoPd nanoparticles (NPs) with controlled compositions were synthesized by the reduction of cobalt acetylacetonate and palladium bromide in the presence of oleylamine and trioctylphosphine. These NPs were active catalysts for hydrogen generation from the hydrolysis of ammonia borane (AB), and their activities were composition dependent. Among the 8 nm CoPd catalysts tested for the hydrolysis of AB, the Co(35)Pd(65) NPs exhibited the highest catalytic activity and durability. Their hydrolysis completion time and activation energy were 5.5 min and 27.5 kJ mol(-1), respectively, which were comparable to the best Pt-based catalyst reported. The catalytic performance of the CoPd/C could be further enhanced by a preannealing treatment at 300 °C under air for 15 h with the hydrolysis completion time reduced to 3.5 min. This high catalytic performance of Co(35)Pd(65) NP catalyst makes it an exciting alternative in pursuit of practical implementation of AB as a hydrogen storage material for fuel cell applications. © 2011 American Chemical Society

Spatial decoupling of light absorption and catalytic activity of Ni-Mo-loaded high-aspect-ratio silicon microwire photocathodes

NASA Astrophysics Data System (ADS)

Vijselaar, Wouter; Westerik, Pieter; Veerbeek, Janneke; Tiggelaar, Roald M.; Berenschot, Erwin; Tas, Niels R.; Gardeniers, Han; Huskens, Jurriaan

2018-03-01

A solar-driven photoelectrochemical cell provides a promising approach to enable the large-scale conversion and storage of solar energy, but requires the use of Earth-abundant materials. Earth-abundant catalysts for the hydrogen evolution reaction, for example nickel-molybdenum (Ni-Mo), are generally opaque and require high mass loading to obtain high catalytic activity, which in turn leads to parasitic light absorption for the underlying photoabsorber (for example silicon), thus limiting production of hydrogen. Here, we show the fabrication of a highly efficient photocathode by spatially and functionally decoupling light absorption and catalytic activity. Varying the fraction of catalyst coverage over the microwires, and the pitch between the microwires, makes it possible to deconvolute the contributions of catalytic activity and light absorption to the overall device performance. This approach provided a silicon microwire photocathode that exhibited a near-ideal short-circuit photocurrent density of 35.5 mA cm-2, a photovoltage of 495 mV and a fill factor of 62% under AM 1.5G illumination, resulting in an ideal regenerative cell efficiency of 10.8%.

Soot Combustion over Nanostructured Ceria with Different Morphologies

PubMed Central

Zhang, Wen; Niu, Xiaoyu; Chen, Liqiang; Yuan, Fulong; Zhu, Yujun

2016-01-01

In this study, nano-structure ceria with three different morphologies (nanorod, nanoparticle and flake) have been prepared by hydrothermal and solvothermal methods. The ceria samples were deeply characterized by XRD, SEM, TEM, H2-TPR, XPS and in-situ DRIFTS, and tested for soot combustion in absence/presence NO atmospheres under loose and tight contact conditions. The prepared ceria samples exhibit excellent catalytic activities, especially, the CeO2 with nanorod (Ce-R) shows the best catalytic activity, for which the peak temperature of soot combustion (Tm) is about 500 and 368 °C in loose and tight contact conditions, respectively. The catalytic activity for Ce-R is higher than that of the reported CeO2 catalysts and reaches a level that of precious metals. The characterization results reveal that the maximal amounts of adsorbed oxygen species on the surface of the nanostructure Ce-R catalyst should be the crucial role to decide the catalytic soot performance. High BET surface area may also be a positive effect on soot oxidation activity under loose contact conditions. PMID:27353143

Novel application of thermally expanded graphite as the support of catalysts for direct synthesis of DMC from CH3OH and CO2.

PubMed

Bian, J; Xiao, M; Wang, S J; Lu, Y X; Meng, Y Z

2009-06-01

Novel Cu-Ni bimetallic catalysts supported on thermally expanded graphite (TEG) were prepared as an example to show the particular characteristics of TEG as a carbon support material. The structures of TEG and the synthesized Cu-Ni/TEG catalysts were characterized using BET, FTIR, TG, SEM, TEM, XRD and TPR techniques. The catalytic activities of the prepared catalysts were investigated by performing micro-reaction in the direct synthesis of dimethyl carbonate (DMC) from CH3OH and CO2. The experimental results indicated that the prepared Cu-Ni/TEG catalysts exhibited highly catalytic activity. Under the optimal catalytic conditions at 100 degrees C and under 1.2 MPa, the highest conversion of CH3OH of 4.97% and high selectivity of DMC of 89.3% can be achieved. The highly catalytic activity of Cu-Ni/TEG in DMC synthesis can be attributed to the synergetic effects of metal Cu, Ni and Cu-Ni alloy in the activation of CH3OH and CO2 and the particular characteristics of TEG as a carbon support material.

Enzymatic Detoxication, Conformational Selection, and the Role of Molten Globule Active Sites*

PubMed Central

Honaker, Matthew T.; Acchione, Mauro; Zhang, Wei; Mannervik, Bengt; Atkins, William M.

2013-01-01

The role of conformational ensembles in enzymatic reactions remains unclear. Discussion concerning “induced fit” versus “conformational selection” has, however, ignored detoxication enzymes, which exhibit catalytic promiscuity. These enzymes dominate drug metabolism and determine drug-drug interactions. The detoxication enzyme glutathione transferase A1–1 (GSTA1–1), exploits a molten globule-like active site to achieve remarkable catalytic promiscuity wherein the substrate-free conformational ensemble is broad with barrierless transitions between states. A quantitative index of catalytic promiscuity is used to compare engineered variants of GSTA1–1 and the catalytic promiscuity correlates strongly with characteristics of the thermodynamic partition function, for the substrate-free enzymes. Access to chemically disparate transition states is encoded by the substrate-free conformational ensemble. Pre-steady state catalytic data confirm an extension of the conformational selection model, wherein different substrates select different starting conformations. The kinetic liability of the conformational breadth is minimized by a smooth landscape. We propose that “local” molten globule behavior optimizes detoxication enzymes. PMID:23649628

Remarkable photo-catalytic degradation of malachite green by nickel doped bismuth selenide under visible light irradiation

NASA Astrophysics Data System (ADS)

Kulsi, Chiranjit; Ghosh, Amrita; Mondal, Anup; Kargupta, Kajari; Ganguly, Saibal; Banerjee, Dipali

2017-01-01

Bismuth selenide (Bi2Se3) and nickel (Ni) doped Bi2Se3 were prepared by a solvothermal approach to explore the photo-catalytic performance of the materials in degradation of malachite green (MG). The presence of nickel was confirmed by X-ray photoelectron spectroscopy (XPS) measurement in doped Bi2Se3. The results showed that the nickel doping played an important role in microstructure and photo-catalytic activity of the samples. Nickel doped Bi2Se3 sample exhibited higher photo-catalytic activity than that of the pure Bi2Se3 sample under visible-light irradiation. The photo-catalytic degradation followed first-order reaction kinetics. Fast degradation kinetics and complete (100% in 5 min of visible light irradiation) removal of MG was achieved by nickel doped Bi2Se3 in presence of hydrogen peroxide (H2O2) due to modification of band gap energies leading to suppression of photo-generated electron-hole recombination.

High-resolution single-molecule fluorescence imaging of zeolite aggregates within real-life fluid catalytic cracking particles.

PubMed

Ristanović, Zoran; Kerssens, Marleen M; Kubarev, Alexey V; Hendriks, Frank C; Dedecker, Peter; Hofkens, Johan; Roeffaers, Maarten B J; Weckhuysen, Bert M

2015-02-02

Fluid catalytic cracking (FCC) is a major process in oil refineries to produce gasoline and base chemicals from crude oil fractions. The spatial distribution and acidity of zeolite aggregates embedded within the 50-150 μm-sized FCC spheres heavily influence their catalytic performance. Single-molecule fluorescence-based imaging methods, namely nanometer accuracy by stochastic chemical reactions (NASCA) and super-resolution optical fluctuation imaging (SOFI) were used to study the catalytic activity of sub-micrometer zeolite ZSM-5 domains within real-life FCC catalyst particles. The formation of fluorescent product molecules taking place at Brønsted acid sites was monitored with single turnover sensitivity and high spatiotemporal resolution, providing detailed insight in dispersion and catalytic activity of zeolite ZSM-5 aggregates. The results point towards substantial differences in turnover frequencies between the zeolite aggregates, revealing significant intraparticle heterogeneities in Brønsted reactivity. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Assembling strategy to synthesize palladium modified kaolin nanocomposites with different morphologies

PubMed Central

Li, Xiaoyu; Ouyang, Jing; Zhou, Yonghua; Yang, Huaming

2015-01-01

Nanocomposites of aluminosilicate minerals, kaolins (kaolinite and halloysite) with natural different morphologies assembling with palladium (Pd) nanoparticles have been successfully synthesized through strong electrostatic adsorption and chemical bonding after surface modification with 3-aminopropyl triethoxysilane (APTES). Meanwhile, the influence of different morphologies supports on catalytic hydrogenation properties was explored. The surface concentration of amino groups on the kaolins was related to the morphology and surface nature. Electronmicroscopy revealed that the monodisperse Pd nanoparticles were uniformly deposited onto the surface of kaolins, ranging in diameter from 0.5 nm to 5.5 nm. The functional groups could not only improve the dispersion of kaolins with different morphologies in solution, but also enhance the interaction between Pd precursors and kaolins, thus preventing small Pd nanoparticles from agglomerating and leading to high activity for the catalytic hydrogenation of styrene. Pd-FK@APTES was more active compared to other samples. Selecting the kaolin morphology with a different surface nature allows the selective surface modification of a larger fraction of the reactive facets on which the active sites can be enriched and tuned. This desirable surface coordination of catalytically active atoms could substantially improve catalytic activity. PMID:26333629

Assembling strategy to synthesize palladium modified kaolin nanocomposites with different morphologies

NASA Astrophysics Data System (ADS)

Li, Xiaoyu; Ouyang, Jing; Zhou, Yonghua; Yang, Huaming

2015-09-01

Nanocomposites of aluminosilicate minerals, kaolins (kaolinite and halloysite) with natural different morphologies assembling with palladium (Pd) nanoparticles have been successfully synthesized through strong electrostatic adsorption and chemical bonding after surface modification with 3-aminopropyl triethoxysilane (APTES). Meanwhile, the influence of different morphologies supports on catalytic hydrogenation properties was explored. The surface concentration of amino groups on the kaolins was related to the morphology and surface nature. Electronmicroscopy revealed that the monodisperse Pd nanoparticles were uniformly deposited onto the surface of kaolins, ranging in diameter from 0.5 nm to 5.5 nm. The functional groups could not only improve the dispersion of kaolins with different morphologies in solution, but also enhance the interaction between Pd precursors and kaolins, thus preventing small Pd nanoparticles from agglomerating and leading to high activity for the catalytic hydrogenation of styrene. Pd-FK@APTES was more active compared to other samples. Selecting the kaolin morphology with a different surface nature allows the selective surface modification of a larger fraction of the reactive facets on which the active sites can be enriched and tuned. This desirable surface coordination of catalytically active atoms could substantially improve catalytic activity.

Assembling strategy to synthesize palladium modified kaolin nanocomposites with different morphologies.

PubMed

Li, Xiaoyu; Ouyang, Jing; Zhou, Yonghua; Yang, Huaming

2015-09-03

Nanocomposites of aluminosilicate minerals, kaolins (kaolinite and halloysite) with natural different morphologies assembling with palladium (Pd) nanoparticles have been successfully synthesized through strong electrostatic adsorption and chemical bonding after surface modification with 3-aminopropyl triethoxysilane (APTES). Meanwhile, the influence of different morphologies supports on catalytic hydrogenation properties was explored. The surface concentration of amino groups on the kaolins was related to the morphology and surface nature. Electronmicroscopy revealed that the monodisperse Pd nanoparticles were uniformly deposited onto the surface of kaolins, ranging in diameter from 0.5 nm to 5.5 nm. The functional groups could not only improve the dispersion of kaolins with different morphologies in solution, but also enhance the interaction between Pd precursors and kaolins, thus preventing small Pd nanoparticles from agglomerating and leading to high activity for the catalytic hydrogenation of styrene. Pd-FK@APTES was more active compared to other samples. Selecting the kaolin morphology with a different surface nature allows the selective surface modification of a larger fraction of the reactive facets on which the active sites can be enriched and tuned. This desirable surface coordination of catalytically active atoms could substantially improve catalytic activity.

A spontaneous change in the oxidation states of Pd/WO3 toward an active phase during catalytic cycles of CO oxidation

NASA Astrophysics Data System (ADS)

Jeon, Byungwook; Kim, Ansoon; Lee, Young-Ahn; Seo, Hyungtak; Kim, Yu Kwon

2017-11-01

CO oxidation over Pd/WO3 films prepared on a glass substrate has been examined at the substrate temperature of 150 - 250 °C and pressures less than 1 Torr with a stoichiometric mixture of CO and O2. Under the given reaction condition, the chemical states of the Pd/WO3 film gradually change into the most catalytically active form with the highest saturation reaction rate regardless of the initial oxidation states. The measured CO oxidation rate over the Pd/WO3 is strongly dependent on the chemical states of Pd and W. Either metallic Pd or fully oxidized PdO phase is not as catalytically active as the active form with mixed metallic Pd and thin PdO layers supported on WO3 with partially reduced W5+ state which is spontaneously obtained during the catalytic reaction cycles. Our results indicate that the facile oxygen transfer between Pd and WO3 layers not only facilitate the spontaneous changes into the active form, but also act as a promotional role in CO oxidation over the Pd layer.

Detection of Intracellular Reduced (Catalytically Active) SHP-1 and Analyses of Catalytically Inactive SHP-1 after Oxidation by Pervanadate or H2O2.

PubMed

Choi, Seeyoung; Love, Paul E

2018-01-05

Oxidative inactivation of cysteine-dependent Protein Tyrosine Phosphatases (PTPs) by cellular reactive oxygen species (ROS) plays a critical role in regulating signal transduction in multiple cell types. The phosphatase activity of most PTPs depends upon a 'signature' cysteine residue within the catalytic domain that is maintained in the de-protonated state at physiological pH rendering it susceptible to ROS-mediated oxidation. Direct and indirect techniques for detection of PTP oxidation have been developed (Karisch and Neel, 2013). To detect catalytically active PTPs, cell lysates are treated with iodoacetyl-polyethylene glycol-biotin (IAP-biotin), which irreversibly binds to reduced (S - ) cysteine thiols. Irreversible oxidation of SHP-1 after treatment of cells with pervanadate or H 2 O 2 is detected with antibodies specific for the sulfonic acid (SO 3 H) form of the conserved active site cysteine of PTPs. In this protocol, we describe a method for the detection of the reduced (S - ; active) or irreversibly oxidized (SO 3 H; inactive) form of the hematopoietic PTP SHP-1 in thymocytes, although this method is applicable to any cysteine-dependent PTP in any cell type.

Effect of point mutations on Herbaspirillum seropedicae NifA activity.

PubMed

Aquino, B; Stefanello, A A; Oliveira, M A S; Pedrosa, F O; Souza, E M; Monteiro, R A; Chubatsu, L S

2015-08-01

NifA is the transcriptional activator of the nif genes in Proteobacteria. It is usually regulated by nitrogen and oxygen, allowing biological nitrogen fixation to occur under appropriate conditions. NifA proteins have a typical three-domain structure, including a regulatory N-terminal GAF domain, which is involved in control by fixed nitrogen and not strictly required for activity, a catalytic AAA+ central domain, which catalyzes open complex formation, and a C-terminal domain involved in DNA-binding. In Herbaspirillum seropedicae, a β-proteobacterium capable of colonizing Graminae of agricultural importance, NifA regulation by ammonium involves its N-terminal GAF domain and the signal transduction protein GlnK. When the GAF domain is removed, the protein can still activate nif genes transcription; however, ammonium regulation is lost. In this work, we generated eight constructs resulting in point mutations in H. seropedicae NifA and analyzed their effect on nifH transcription in Escherichia coli and H. seropedicae. Mutations K22V, T160E, M161V, L172R, and A215D resulted in inactive proteins. Mutations Q216I and S220I produced partially active proteins with activity control similar to wild-type NifA. However, mutation G25E, located in the GAF domain, resulted in an active protein that did not require GlnK for activity and was partially sensitive to ammonium. This suggested that G25E may affect the negative interaction between the N-terminal GAF domain and the catalytic central domain under high ammonium concentrations, thus rendering the protein constitutively active, or that G25E could lead to a conformational change comparable with that when GlnK interacts with the GAF domain.

Effect of point mutations on Herbaspirillum seropedicae NifA activity

PubMed Central

Aquino, B.; Stefanello, A.A.; Oliveira, M.A.S.; Pedrosa, F.O.; Souza, E.M.; Monteiro, R.A.; Chubatsu, L.S.

2015-01-01

NifA is the transcriptional activator of the nif genes in Proteobacteria. It is usually regulated by nitrogen and oxygen, allowing biological nitrogen fixation to occur under appropriate conditions. NifA proteins have a typical three-domain structure, including a regulatory N-terminal GAF domain, which is involved in control by fixed nitrogen and not strictly required for activity, a catalytic AAA+ central domain, which catalyzes open complex formation, and a C-terminal domain involved in DNA-binding. In Herbaspirillum seropedicae, a β-proteobacterium capable of colonizing Graminae of agricultural importance, NifA regulation by ammonium involves its N-terminal GAF domain and the signal transduction protein GlnK. When the GAF domain is removed, the protein can still activate nif genes transcription; however, ammonium regulation is lost. In this work, we generated eight constructs resulting in point mutations in H. seropedicae NifA and analyzed their effect on nifH transcription in Escherichia coli and H. seropedicae. Mutations K22V, T160E, M161V, L172R, and A215D resulted in inactive proteins. Mutations Q216I and S220I produced partially active proteins with activity control similar to wild-type NifA. However, mutation G25E, located in the GAF domain, resulted in an active protein that did not require GlnK for activity and was partially sensitive to ammonium. This suggested that G25E may affect the negative interaction between the N-terminal GAF domain and the catalytic central domain under high ammonium concentrations, thus rendering the protein constitutively active, or that G25E could lead to a conformational change comparable with that when GlnK interacts with the GAF domain. PMID:26176311

Structural coupling of SH2-kinase domains links Fes and Abl substrate recognition and kinase activation.

PubMed

Filippakopoulos, Panagis; Kofler, Michael; Hantschel, Oliver; Gish, Gerald D; Grebien, Florian; Salah, Eidarus; Neudecker, Philipp; Kay, Lewis E; Turk, Benjamin E; Superti-Furga, Giulio; Pawson, Tony; Knapp, Stefan

2008-09-05

The SH2 domain of cytoplasmic tyrosine kinases can enhance catalytic activity and substrate recognition, but the molecular mechanisms by which this is achieved are poorly understood. We have solved the structure of the prototypic SH2-kinase unit of the human Fes tyrosine kinase, which appears specialized for positive signaling. In its active conformation, the SH2 domain tightly interacts with the kinase N-terminal lobe and positions the kinase alphaC helix in an active configuration through essential packing and electrostatic interactions. This interaction is stabilized by ligand binding to the SH2 domain. Our data indicate that Fes kinase activation is closely coupled to substrate recognition through cooperative SH2-kinase-substrate interactions. Similarly, we find that the SH2 domain of the active Abl kinase stimulates catalytic activity and substrate phosphorylation through a distinct SH2-kinase interface. Thus, the SH2 and catalytic domains of active Fes and Abl pro-oncogenic kinases form integrated structures essential for effective tyrosine kinase signaling.

Improved activity of immobilized horseradish peroxidase on gold nanoparticles in the presence of bovine serum albumin

NASA Astrophysics Data System (ADS)

Ni, Yuyang; Li, Jun; Huang, Zhenzhen; He, Ke; Zhuang, Jiaqi; Yang, Wensheng

2013-11-01

The using of macromolecular additives is known to be a simple and effective way to improve the activity of immobilized enzymes on solid support, yet the mechanism has not been well understood. Taking horseradish peroxidase (HRP) as an example, only 30 % of its catalytic activity was kept after being immobilized on the surface of 25-nm Au nanoparticles, mainly attributed to the conformational change of the heme-containing active site. The catalytic activity of HRP was significantly improved to 80 % when a certain amount of bovine serum albumin (BSA) was added at the initial stage of the immobilization. Systematic spectral investigation indicated that the addition of BSA inhibited the tertiary structure change around the active site, which was a prerequisite for improved activity of the immobilized HRP. Steady-state kinetic analyses revealed that the introduction of BSA could effectively improve the turnover rate of substrate to product in spite of slight reduced affinity to substrates, which also contributed to the improved catalytic activity.

Responses of soil hydrolase kinetics to nitrogen and phosphorus additions in Chinese fir plantations of subtropical China

NASA Astrophysics Data System (ADS)

Zhang, X.; Zhang, C.; Yang, Y.; Wang, H.; Chen, F.; Fu, X.; Fang, X.; Sun, X.

2016-12-01

Nitrogen (N) deposition and low soil phosphorus (P) content aggravate the P limitation in subtropical forest soils. However, the responses of soil organic matter related hydrolyase kinetics to N and P additions in subtropical plantations are still not clear. We tested the hypothesis that P application can improve the potential maximum activities of soil carbon (C) and N related hydrolayase but substrate demand (Km) may tradeoff the catalytic efficiency of the enzymes. Thirty 20m×20m plots were established in November 2011 and six different treatments were randomly distributed with five replicates in the Chinese fir plantations in subtropical China. The ongoing treatments are control (CK, no N and P application), low N addition (N1:50 kg N ha-1 yr-1), high N addition (N2: 100 kg N ha-1 yr-1), P addition (P: 50 kg P ha-1 yr-1), low N andP addition (N1P: 50 kg N ha-1 yr-1 and 50 kg P ha-1 yr-1) and high N and P addition (N2P: 100 kg N ha-1yr-1and 50 kg P ha-1 yr-1). Soil enzyme kinetic parameters for b-1,4-glucosidase (βG), β-1,4-N-acetylglucosaminidase (NAG), and acid phosphatase (aP) were measured in November 2015. The substrate affinities (Km) of βG and NAG were not affected by N or /and P additions. However, the substrate affinities of aP were decreased by N additions (N1, N2) with higher Km values than the other treatments. N additions (N1, N2) or higher N combined P additions (N2P) increased Vmax and catalytic efficiencies for βG, while with P addition treatments (N1P, N2P, and P) decreased Vmax and catalytic efficiencies for aP. The effects of N combined P treatments (N1P and N2P) on kinetic parameters (Vmax, Km) and catalytic efficiencies for AP were similar to P treatment, indicating that P had stronger effects on organic phosphorus hydrolysis than N in the research site. The N additions (N1 and N2) did not affect the catalytic efficiencies for NAG despite of their positive responses to Vmax for NAG compared with CK. The catalytic efficiencies of aP and NAG were negatively correlated with soil TP and available P contents, and both the enzyme kinetics for aP exhibited strong negative correlations with TP and available P contents. However, the Vmax for BG and NAG were positively correlated with SOC contents, but were negatively correlated with soil pH.

Functional Effects of Genetic Polymorphisms in the N-acetyltransferase 1 Coding and 3′ Untranslated Regions

PubMed Central

Zhu, Yuanqi; States, J. Christopher; Wang, Yang; Hein, David W.

2011-01-01

BACKGROUND The functional effects of N-acetyltransferase 1 (NAT1) polymorphisms and haplotypes are poorly understood, compromising the validity of associations reported with diseases including birth defects and numerous cancers. METHODS We investigated the effects of genetic polymorphisms within the NAT1 coding region and the 3′-untranslated region (3′-UTR) and their associated haplotypes on N- and O-acetyltransferase catalytic activities, and NAT1 mRNA and protein levels following recombinant expression in COS-1 cells. RESULTS 1088T>A (rs1057126; 3′-UTR) and 1095C>A (rs15561; 3′-UTR) each slightly reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. A 9-base pair (TAATAATAA) deletion between nucleotides 1065-1090 (3′-UTR) reduced NAT1 catalytic activity and NAT1 mRNA and protein levels. In contrast, a 445G>A (rs4987076; V149I), 459G>A (rs4986990; T153T), 640T>G (rs4986783; S214A) coding region haplotype present in NAT1*11 increased NAT1 catalytic activity and NAT1 protein, but not NAT1 mRNA levels. A combination of the 9-base pair (TAATAATAA) deletion and the 445G>A, 459G>A, 640T>G coding region haplotypes, both present in NAT1*11, appeared to neutralize the opposing effects on NAT1 protein and catalytic activity, resulting in levels of NAT1 protein and catalytic activity that did not differ significantly from the NAT1*4 reference. CONCLUSIONS Since 1095C>A (3′-UTR) is the sole polymorphism present in NAT1*3, our data suggests that NAT1*3 is not functionally equivalent to the NAT1*4 reference. Furthermore, our findings provide biological support for reported associations of 1088T>A and 1095C>A polymorphisms with birth defects. PMID:21290563