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.

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.

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.

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

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.

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.

LETTER TO THE EDITOR: Single-species reactions on a random catalytic chain

NASA Astrophysics Data System (ADS)

Oshanin, G.; Burlatsky, S. F.

2002-11-01

We present an exact solution for a catalytically activated annihilation A + A → 0 reaction taking place on a one-dimensional chain in which some segments (placed at random, with mean concentration p) possess special, catalytic properties. An annihilation reaction takes place as soon as any two A particles land from the reservoir onto two vacant sites at the extremities of the catalytic segment, or when any A particle lands onto a vacant site on a catalytic segment while the site at the other extremity of this segment is already occupied by another A particle. We find that the disorder-average pressure P(quen) per site of such a chain is given by P(quen) = P(Lan) + β-1F, where P(Lan) = β-1 ln(1 + z) is the Langmuir adsorption pressure, (z being the activity and β-1 the temperature), while β-1F is the reaction-induced contribution, which can be expressed, under appropriate change of notation, as the Lyapunov exponent for the product of 2 × 2 random matrices, obtained exactly by Derrida and Hilhorst (1983 J. Phys. A: Math. Gen. 16 2641). Explicit asymptotic formulae for the particle mean density and the compressibility are also presented.

Influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for the synthesis of dimethyl carbonate

NASA Astrophysics Data System (ADS)

Zhang, Guoqiang; Li, Zhong; Zheng, Huayan; Hao, Zhiqiang; Wang, Xia; Wang, Jiajun

2016-12-01

Activated carbon (AC) supported Cu catalysts are employed to study the influence of surface oxygenated groups on the formation of active Cu species and the catalytic activity of Cu/AC catalyst for oxidative carbonylation of methanol to dimethyl carbonate (DMC). The AC supports are thermal treated under different temperatures in order to adjust the levels of surface oxygenated groups. The AC supports are characterized by BET, TPD-MS and XRD, and the Cu/AC catalysts are characterized by BET, XRD, TEM, XPS, AAS, CH3OH-TPD and N2O chemisorption. The results show that as the treatment temperature is below 800 °C, the BET surface area of the corresponding AC supports are nearly unchanged and close to that of the original AC (1529.6 m2/g). But as the thermal treatment temperature is elevated from 1000 to 1600 °C, the BET surface area of AC supports gradually decreases from 1407.6 to 972.2 m2/g. After loading of Cu, the BET surface area of copper catalysts is in the range of 834.4 to 1545.3 m2/g, which is slightly less than that of the respective supports. When AC is thermal treated at 400 and 600 °C, the unstable carboxylic acid and anhydrides groups are selectively removed, which has weakened the mobility and agglomeration of Cu species during the calcination process, and thus improve the Cu species dispersion over AC support. But as the treatment temperature is elevated from 600 °C to 1200 °C, the Cu species dispersion begins to decline suggesting further removal of stable surface oxygenated groups is unfavorable for Cu species dispersion. Moreover, higher thermal treatment temperature (above 1200 °C) promotes the graphitization degree of AC and leds to the decrease of Cu loading on AC support. Meanwhile, the removal of surface oxygenated groups by thermal treatment is conducive to the formation of more π-sites, and thus promote the reduction of Cu2+ to Cu+ and Cu0 as active centers. The specific surface area of (Cu+ + Cu0) is improved by thermal treatment of AC

Catalytic and regulatory roles of species involved in metal-nucleotide equilibriums in human pyridoxal kinase.

PubMed

Navarro, Freddy; Ramírez-Sarmiento, César A; Guixé, Victoria

2013-10-01

Pyridoxal 5'-phosphate is the active form of vitamin B6 and its deficiency is directly related with several human disorders, which make human pyridoxal kinase (hPLK) an important pharmacologic target. In spite of this, a carefully kinetic characterization of hPLK including the main species that regulates the enzymatic activity is at date missing. Here we analyse the catalytic and regulatory mechanisms of hPLK as a function of a precise determination of the species involved in metal-nucleotide equilibriums and describe new regulatory mechanisms for this enzyme. hPLK activity is supported by several metals, being Zn(2+) the most effective, although the magnitude of the effect observed is highly dependent on the relative concentrations of metal and nucleotide used. The true substrate for the reaction catalyzed by hPLK is the metal nucleotide complex, while ATP(4-) and HATP(3-) did not affect the activity. The enzyme presents substrate inhibition by both pyridoxal (PL) and ZnATP(2-), although the latter behaves as a weakly inhibitor. Our study also established, for the first time, a dual role for free Zn(2+); as an activator at low concentrations (19 μM optimal concentration) and as a potent inhibitor with a IC50 of 37 μM. These results highlighted the importance of an accurate estimation of the actual concentration of the species involved in metal-nucleotide equilibriums in order to obtain reliable values for the kinetic parameters, and for determine the true regulators of the PLK activity. They also help to explain the dissimilar kinetic parameters reported in the literature for this enzyme.

Large stability and high catalytic activities of sub-nm metal (0) clusters: implications into the nucleation and growth theory.

PubMed

Piñeiro, Yolanda; Buceta, David; Calvo, Javier; Huseyinova, Shahana; Cuerva, Miguel; Pérez, Ángel; Domínguez, Blanca; López-Quintela, M Arturo

2015-07-01

Clusters are stable catalytic species, which are produced during the synthesis of nanoparticles (NPs). Their existence contradicts the thermodynamic principles used to explain the formation of NPs by the classical nucleation and growth theories (NGTs). Using chemical and electrochemical methods we will show that depending on the experimental conditions one can produce either Ag clusters or Ag NPs. Moreover, using already prepared Ag clusters one can observe the disappearance of the usual induction period observed for the kinetics of NP formation, indicating that clusters catalyze the formation of NPs. Taking these data together with some previous examples of cluster-catalyzed anisotropic growth, we derived a qualitative approach to include the catalytic activities of clusters into the formation of NPs, which is incorporated into the NGT. Some qualitative conclusions about the main experimental parameters, which affect the formation of clusters versus NPs, as well as the catalytic mechanism versus the non-catalytic one, are also described. Copyright © 2015 Elsevier Inc. All rights reserved.

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

DOE PAGES

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

2015-03-04

Ab initio Molecular Dynamics simulations and static Density Functional Theory calculations have been performed to investigate the reaction mechanism of CO oxidation on Au/CeO 2 catalyst. It is found that under reaction condition CO adsorption significantly labializes the surface atoms of the Au cluster and leads to the formation of isolated Au+-CO species that resides on the support in the vicinity of the Au particle. In this context, we identified a dynamic single-atom catalytic mechanism at the interfacial area for CO oxidation on Au/CeO 2 catalyst, which is a lower energy pathway than that of CO oxidation at the interfacemore » with the metal particle. This results from the ability of the single atom site to strongly couple with the redox properties of the support in a synergistic manner thereby lowering the barrier for redox reactions. We find that the single Au+ ion, which only exists under reaction conditions, breaks away from the Au cluster to catalyze CO oxidation and returns to the Au cluster after the catalytic cycle is completed. Generally, our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in a catalytic process.« less

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.

Effect of Redox “Non-Innocent” Linker on the Catalytic Activity of Copper-Catecholate-Decorated Metal–Organic Frameworks

DOE PAGES

Zhang, Xuan; Vermeulen, Nicolaas A.; Huang, Zhiyuan; ...

2017-12-26

Two new UiO-68 type of Zr-MOFs featuring redox non-innocent catechol-based linkers of different redox activities have been synthesized through a de novo mixed-linker strategy. Also, metalation of the MOFs with Cu(II) precursors triggers the reduction of Cu(II) by the phenyl-catechol groups to Cu(I) with the concomitant formation of semiquinone radicals as evidenced by EPR and XPS characterization. The MOF-supported catalysts are selective toward the allylic oxidation of cyclohexene and it is found that the presence of in situ-generated Cu(I) species exhibits enhanced catalytic activity as compared to a similar MOF with Cu(II) metalated naphthalenyl-dihydroxy groups. Here, this work unveils themore » importance of metal-support redox interactions in the catalytic activity of MOF-supported catalysts which are not easily accessible in traditional metal oxide supports.« less

Effect of Redox “Non-Innocent” Linker on the Catalytic Activity of Copper-Catecholate-Decorated Metal–Organic Frameworks

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

Zhang, Xuan; Vermeulen, Nicolaas A.; Huang, Zhiyuan

Two new UiO-68 type of Zr-MOFs featuring redox non-innocent catechol-based linkers of different redox activities have been synthesized through a de novo mixed-linker strategy. Also, metalation of the MOFs with Cu(II) precursors triggers the reduction of Cu(II) by the phenyl-catechol groups to Cu(I) with the concomitant formation of semiquinone radicals as evidenced by EPR and XPS characterization. The MOF-supported catalysts are selective toward the allylic oxidation of cyclohexene and it is found that the presence of in situ-generated Cu(I) species exhibits enhanced catalytic activity as compared to a similar MOF with Cu(II) metalated naphthalenyl-dihydroxy groups. Here, this work unveils themore » importance of metal-support redox interactions in the catalytic activity of MOF-supported catalysts which are not easily accessible in traditional metal oxide supports.« less

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

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.

Catalytic activity of nanostructured Au: Scale effects versus bimetallic/bifunctional effects in low-temperature CO oxidation on nanoporous Au

PubMed Central

Wang, Lu-Cun; Zhong, Yi; Jin, Haijun; Widmann, Daniel; Weissmüller, Jörg

2013-01-01

Summary The catalytic properties of nanostructured Au and their physical origin were investigated by using the low-temperature CO oxidation as a test reaction. In order to distinguish between structural effects (structure–activity correlations) and bimetallic/bifunctional effects, unsupported nanoporous gold (NPG) samples prepared from different Au alloys (AuAg, AuCu) by selective leaching of a less noble metal (Ag, Cu) were employed, whose structure (surface area, ligament size) as well as their residual amount of the second metal were systematically varied by applying different potentials for dealloying. The structural and chemical properties before and after 1000 min reaction were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The catalytic behavior was evaluated by kinetic measurements in a conventional microreactor and by dynamic measurements in a temporal analysis of products (TAP) reactor. The data reveal a clear influence of the surface contents of residual Ag and Cu species on both O2 activation and catalytic activity, while correlations between activity and structural parameters such as surface area or ligament/crystallite size are less evident. Consequences for the mechanistic understanding and the role of the nanostructure in these NPG catalysts are discussed. PMID:23503603

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

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.

Outstanding catalytic activity of ultra-pure platinum nanoparticles.

PubMed

Januszewska, Aneta; Dercz, Grzegorz; Piwowar, Justyna; Jurczakowski, Rafal; Lewera, Adam

2013-12-09

Small (4 nm) nanoparticles with a narrow size distribution, exceptional surface purity, and increased surface order, which exhibits itself as an increased presence of basal crystallographic planes, can be obtained without the use of any surfactant. These nanoparticles can be used in many applications in an as-received state and are threefold more active towards a model catalytic reaction (oxidation of ethylene glycol). Furthermore, the superior properties of this material are interesting not only due to the increase in their intrinsic catalytic activity, but also due to the exceptional surface purity itself. The nanoparticles can be used directly (i.e., as-received, without any cleaning steps) in biomedical applications (i.e., as more efficient drug carriers due to an increased number of adsorption sites) and in energy-harvesting/data-storage devices. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Active Site Characterization of Proteases Sequences from Different Species of Aspergillus.

PubMed

Morya, V K; Yadav, Virendra K; Yadav, Sangeeta; Yadav, Dinesh

2016-09-01

A total of 129 proteases sequences comprising 43 serine proteases, 36 aspartic proteases, 24 cysteine protease, 21 metalloproteases, and 05 neutral proteases from different Aspergillus species were analyzed for the catalytically active site residues using MEROPS database and various bioinformatics tools. Different proteases have predominance of variable active site residues. In case of 24 cysteine proteases of Aspergilli, the predominant active site residues observed were Gln193, Cys199, His364, Asn384 while for 43 serine proteases, the active site residues namely Asp164, His193, Asn284, Ser349 and Asp325, His357, Asn454, Ser519 were frequently observed. The analysis of 21 metalloproteases of Aspergilli revealed Glu298 and Glu388, Tyr476 as predominant active site residues. In general, Aspergilli species-specific active site residues were observed for different types of protease sequences analyzed. The phylogenetic analysis of these 129 proteases sequences revealed 14 different clans representing different types of proteases with diverse active site residues.

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.

[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.

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.

How low does iron go? Chasing the active species in fe-catalyzed cross-coupling reactions.

PubMed

Bedford, Robin B

2015-05-19

The catalytic cross-coupling reactions of organic halides or related substrates with organometallic nucleophiles form the cornerstone of many carbon-carbon bond-forming processes. While palladium-based catalysts typically mediate such reactions, there are increasing concerns about the long-term sustainability of palladium in synthesis. This is due to the high cost of palladium, coupled with its low natural abundance, environmentally deleterious extraction (∼6 g of metal are produced per ton of ore), toxicity, and competition for its use from the automotive and consumer electronics sectors. Therefore, there is a growing interest in replacing palladium-based catalysts with those incorporating more earth-abundant elements. With its low cost, high natural abundance, and low toxicity, iron makes a particularly appealing alternative, and accordingly, the development of iron-catalyzed cross-coupling is undergoing explosive growth. However, our understanding of the mechanisms that underpin the iron-based catalytic cycles is still very much in its infancy. Mechanistic insight into catalytic reactions is not only academically important but also allows us to maximize the efficiency of processes or even to develop entirely new transformations. Key to the development of robust mechanistic models for cross-coupling is knowing the lowest oxidation state in the cycle. Once this is established, we can explore subsequent redox processes and build the catalytic manifold. Until we know with confidence what the lowest oxidation state is, any cycles proposed are largely just guesswork. To date, Fe(-II), Fe(-I), Fe(0), Fe(I), and Fe(II) have been proposed as contenders for the lowest-oxidation-state species in the cycle in iron-catalyzed cross-coupling; the aim of this Account is to pull together the various pieces of evidence in support, or otherwise, of each of these suggestions in turn. There currently exists no direct evidence that oxidation states below Fe(0) are active in the

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.

Electrochemically assisted localized etching of ZnO single crystals in water using a catalytically active Pt-coated atomic force microscopy probe

NASA Astrophysics Data System (ADS)

Shibata, Takayuki; Yamamoto, Kota; Sasano, Junji; Nagai, Moeto

2017-09-01

This paper presents a nanofabrication technique based on the electrochemically assisted chemical dissolution of zinc oxide (ZnO) single crystals in water at room temperature using a catalytically active Pt-coated atomic force microscopy (AFM) probe. Fabricated grooves featured depths and widths of several tens and several hundreds of nanometers, respectively. The material removal rate of ZnO was dramatically improved by controlling the formation of hydrogen ions (H+) on the surface of the catalytic Pt-coated probe via oxidation of H2O molecules; this reaction can be enhanced by applying a cathodic potential to an additional Pt-wire working electrode in a three-electrode configuration. Consequently, ZnO can be dissolved chemically in water as a soluble Zn2+ species via a reaction with H+ species present in high concentrations in the immediate vicinity of the AFM tip apex.

[Catalytic performance of Ce/Zr series catalysts on soot combustion].

PubMed

Zhu, Ling; Wang, Xue-Zhong; Hao, Zheng-Ping

2005-09-01

Catalytic performances of Ce/Zr series catalysts (Ce(x)Zr(1-x)O2) on soot combustion and the influence of feed gas were investigated by TG and TPO. The catalytic activity is high, and affects by the Ce/Zr ratio. The concentration of O2 affects the speed-limited step during the process of soot combustion. H2O showed no effect on the catalytic activity for soot combustion on Ce(0.5)Zr(0.5)O2. NO could promote soot combustion by presenting NO2, a more powerful oxidant than O2, and the ignition temperature of soot decreased 30 degrees C. Results of TG and TPO show that the beta species oxygen on the catalyst take part in the combustion process.

Promoting effect of alkaline earth metal doping on catalytic activity of HC and NOx conversion over Pd-only three-way catalyst.

PubMed

Yang, Linyan; Lin, Siyu; Yang, Xue; Fang, Weimin; Zhou, Renxian

2014-08-30

The influence of alkaline earth metal (M=Mg, Ca, Sr and Ba) promoter on the structural/textural properties of Ce0.67Zr0.33O2 (designated as CZ) and the catalytic behavior of its supported Pd-only three-way catalyst (Pd/CZM) have been investigated. The results show that the modification with alkaline earth metal obviously improves the catalytic activity for hydrocarbon (HC) and nitrogen oxides (NOx) conversion, especially the introduction of Ba. Furthermore, the operation window of the promoted catalysts has also been widened. The doping of alkaline earth metal leads to the formation of more homogeneous Ce-Zr-M ternary solid solution with higher surface area and smaller crystallite size, and the corresponding Pd/CZM catalysts present improved reducibility of PdO species. The modification with Ca, Sr and Ba improves the thermal aging resistance, especially Ba. DRIFTS results reveal that the doping of alkaline earth metal enhances the oxygen and electron transfer ability and favors the dissociation of NO, which promotes the activation and storage capacity of the acidic atoms like NOx, and leads to enhanced catalytic activity performance. Copyright © 2014 Elsevier B.V. All rights reserved.

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.

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%.

Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

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

He, Qian; Freakley, Simon J.; Edwards, Jennifer K.

The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviors after heat treatment of Au/FeO x materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed tomore » reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. As a result, correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeO x catalyst.« less

Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation

DOE PAGES

He, Qian; Freakley, Simon J.; Edwards, Jennifer K.; ...

2016-09-27

The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviors after heat treatment of Au/FeO x materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed tomore » reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. As a result, correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeO x catalyst.« less

Population and hierarchy of active species in gold iron oxide catalysts for carbon monoxide oxidation.

PubMed

He, Qian; Freakley, Simon J; Edwards, Jennifer K; Carley, Albert F; Borisevich, Albina Y; Mineo, Yuki; Haruta, Masatake; Hutchings, Graham J; Kiely, Christopher J

2016-09-27

The identity of active species in supported gold catalysts for low temperature carbon monoxide oxidation remains an unsettled debate. With large amounts of experimental evidence supporting theories of either gold nanoparticles or sub-nm gold species being active, it was recently proposed that a size-dependent activity hierarchy should exist. Here we study the diverging catalytic behaviours after heat treatment of Au/FeO x materials prepared via co-precipitation and deposition precipitation methods. After ruling out any support effects, the gold particle size distributions in different catalysts are quantitatively studied using aberration corrected scanning transmission electron microscopy (STEM). A counting protocol is developed to reveal the true particle size distribution from HAADF-STEM images, which reliably includes all the gold species present. Correlation of the populations of the various gold species present with catalysis results demonstrate that a size-dependent activity hierarchy must exist in the Au/FeO x catalyst.

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...

Exponential growth for self-reproduction in a catalytic reaction network: relevance of a minority molecular species and crowdedness

NASA Astrophysics Data System (ADS)

Kamimura, Atsushi; Kaneko, Kunihiko

2018-03-01

Explanation of exponential growth in self-reproduction is an important step toward elucidation of the origins of life because optimization of the growth potential across rounds of selection is necessary for Darwinian evolution. To produce another copy with approximately the same composition, the exponential growth rates for all components have to be equal. How such balanced growth is achieved, however, is not a trivial question, because this kind of growth requires orchestrated replication of the components in stochastic and nonlinear catalytic reactions. By considering a mutually catalyzing reaction in two- and three-dimensional lattices, as represented by a cellular automaton model, we show that self-reproduction with exponential growth is possible only when the replication and degradation of one molecular species is much slower than those of the others, i.e., when there is a minority molecule. Here, the synergetic effect of molecular discreteness and crowding is necessary to produce the exponential growth. Otherwise, the growth curves show superexponential growth because of nonlinearity of the catalytic reactions or subexponential growth due to replication inhibition by overcrowding of molecules. Our study emphasizes that the minority molecular species in a catalytic reaction network is necessary for exponential growth at the primitive stage of life.

Engineering a hyper-catalytic enzyme by photo-activated conformation modulation

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

Agarwal, Pratul K

2012-01-01

Enzyme engineering for improved catalysis has wide implications. We describe a novel chemical modification of Candida antarctica lipase B that allows modulation of the enzyme conformation to promote catalysis. Computational modeling was used to identify dynamical enzyme regions that impact the catalytic mechanism. Surface loop regions located distal to active site but showing dynamical coupling to the reaction were connected by a chemical bridge between Lys136 and Pro192, containing a derivative of azobenzene. The conformational modulation of the enzyme was achieved using two sources of light that alternated the azobenzene moiety in cis and trans conformations. Computational model predicted thatmore » mechanical energy from the conformational fluctuations facilitate the reaction in the active-site. The results were consistent with predictions as the activity of the engineered enzyme was found to be enhanced with photoactivation. Preliminary estimations indicate that the engineered enzyme achieved 8-52 fold better catalytic activity than the unmodulated enzyme.« less

Strong catalytic activity of iron nanoparticles on the surfaces of reduced olivine

NASA Astrophysics Data System (ADS)

Tucker, William C.; Quadery, Abrar H.; Schulte, Alfons; Blair, Richard G.; Kaden, William E.; Schelling, Patrick K.; Britt, Daniel T.

2018-01-01

It is demonstrated that olivine powders heated to subsolidus temperatures in reducing conditions can develop significant concentrations of 10-50 nm diameter Fe nanoparticles on grain surfaces and that these display strong catalytic activity not observed in powders without Fe nanoparticles. Reduced surfaces were exposed to NH3, CO, and H2, volatiles that may be present on the surfaces of comet and volatile-rich asteroids. In the case of NH3 exposure, rapid decomposition was observed. When exposed to a mixture of CO and H2, significant coking of the mineral surfaces occurred. Analysis of the mineral grains after reaction indicated primarily the presence of graphene or graphitic carbon. The results demonstrate that strong chemical activity can be expected at powders that contain nanophase Fe particles. This suggests space-weathered mineral surfaces may play an important role in the synthesis and processing of organic species. This processing may be part of the weathering processes of volatile-rich but atmosphereless solar-system bodies.

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.

Molecular-orbital models for the catalytic activity and selectivity of coordinatively unsaturated platinum surfaces and complexes

NASA Astrophysics Data System (ADS)

Balazs, A. C.; Johnson, K. H.

1982-01-01

Electronic structures have been calculated for 5-, 6-, and 10-atom Pt clusters, as well as for a Pt(PH 3) 4 coordination complex, using the self-consistent-field X-alpha scattered-wave (SCF-Xα-SW) molecular-orbital technique. The 10-atom cluster models the local geometry of a flat, unreconstructed Pt(100) surface, while the 5- and 6-atom clusters show features of a stepped Pt surface. Pt(PH 3) 4 resembles the chemically similar homogeneous catalyst Pt(PPh 3) 4. Common to all these coordinatively unsaturated complexes are orbitals lying near or coinciding with the highest occupied molecular orbital ("Fermi level") which show pronounced d lobes pointing directly into the vacuum. Under the hypothesis that these molecular orbitals are mainly responsible for the chemical activities of the above species, one can account for the relative similarities and differences in catalytic activity and selectivity displayed by unreconstructed Pt(100) surfaces, stepped Pt surfaces or particles, and isolated Pt(PPh 3) 4 coordination complexes. The relevance of these findings to catalyst-support interactions is also discussed. Finally, relativistic corrections to the electronic structures are calculated and their implications on catalytic properties discussed.

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

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

Method to produce catalytically active nanocomposite coatings

DOEpatents

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

2016-02-09

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

Catalytic ozonation of dimethyl phthalate over cerium supported on activated carbon.

PubMed

Li, Laisheng; Ye, Weiying; Zhang, Qiuyun; Sun, Fengqiang; Lu, Ping; Li, Xukai

2009-10-15

Cerium supported on activated carbon (Ce/AC), which was prepared by dipping method, was employed to degrade dimethyl phthalate (DMP) in water. The mineral matter present in the activated carbon positively contributes to its activity to enhance DMP ozonation process. A higher dipping Ce(NO(3))(3) concentration and calcination process increase its microporous volume and surface area, and decreases its exterior surface area. The catalytic activity reaches optimal when 0.2% (w/w) cerium is deposited on activated carbon. Ce/AC catalyst was characterized by XRD, SEM and BET. The presence of either activated carbon or Ce/AC catalyst considerably improves their degradation and mineralization in the ozonation of DMP. During the ozonation (50mg/h ozone flow rate) of a 30 mg/L DMP (initial pH 5.0) with the presence of Ce/AC catalyst, TOC removal rate reaches 68% at 60 min oxidation time, 48% using activated carbon as catalyst, only 22% with ozonation alone. The presence of tert-butanol (a well known OH radical scavenger) strongly inhibits DMP degradation by activated carbon or Ce/AC catalytic ozonation. TOC removal rate follows the second-order kinetics model well. In the ozonation of DMP with 50mg/h ozone flow rate, its mineralization rate constant with the presence of Ce/AC catalyst is 2.5 times higher than that of activated carbon, 7.5 times higher than that of O(3) alone. Ce/AC catalyst shows the better catalytic activity and stability based on 780 min sequential reaction in the ozonation of DMP. Ce/AC was a promising catalyst for ozonizing organic pollutants in the aqueous solution.

Topological entropy of catalytic sets: Hypercycles revisited

NASA Astrophysics Data System (ADS)

Sardanyés, Josep; Duarte, Jorge; Januário, Cristina; Martins, Nuno

2012-02-01

The dynamics of catalytic networks have been widely studied over the last decades because of their implications in several fields like prebiotic evolution, virology, neural networks, immunology or ecology. One of the most studied mathematical bodies for catalytic networks was initially formulated in the context of prebiotic evolution, by means of the hypercycle theory. The hypercycle is a set of self-replicating species able to catalyze other replicator species within a cyclic architecture. Hypercyclic organization might arise from a quasispecies as a way to increase the informational containt surpassing the so-called error threshold. The catalytic coupling between replicators makes all the species to behave like a single and coherent evolutionary multimolecular unit. The inherent nonlinearities of catalytic interactions are responsible for the emergence of several types of dynamics, among them, chaos. In this article we begin with a brief review of the hypercycle theory focusing on its evolutionary implications as well as on different dynamics associated to different types of small catalytic networks. Then we study the properties of chaotic hypercycles with error-prone replication with symbolic dynamics theory, characterizing, by means of the theory of topological Markov chains, the topological entropy and the periods of the orbits of unimodal-like iterated maps obtained from the strange attractor. We will focus our study on some key parameters responsible for the structure of the catalytic network: mutation rates, autocatalytic and cross-catalytic interactions.

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

Synthesis and activity of histidine-containing catalytic peptide dendrimers.

PubMed

Delort, Estelle; Nguyen-Trung, Nhat-Quang; Darbre, Tamis; Reymond, Jean-Louis

2006-06-09

Peptide dendrimers built by iteration of the diamino acid dendron Dap-His-Ser (His = histidine, Ser = Serine, Dap = diamino propionic acid) display a strong positive dendritic effect for the catalytic hydrolysis of 8-acyloxypyrene 1,3,6-trisulfonates, which proceeds with enzyme-like kinetics in aqueous medium (Delort, E.; Darbre, T.; Reymond, J.-L. J. Am. Chem. Soc. 2004, 126, 15642-3). Thirty-two mutants of the original third generation dendrimer A3 ((Ac-His-Ser)8(Dap-His-Ser)4(Dap-His-Ser)2Dap-His-Ser-NH2) were prepared by manual synthesis or by automated synthesis with use of a Chemspeed PSW1100 peptide synthesizer. Dendrimer catalysis was specific for 8-acyloxypyrene 1,3,6-trisulfonates, and there was no activity with other types of esters. While dendrimers with hydrophobic residues at the core and histidine residues at the surface only showed weak activity, exchanging serine residues in dendrimer A3 against alanine (A3A), beta-alanine (A3B), or threonine (A3C) improved catalytic efficiency. Substrate binding was correlated with the total number of histidines per dendrimer, with an average of three histidines per substrate binding site. The catalytic rate constant kcat depended on the placement of histidines within the dendrimers and the nature of the other amino acid residues. The fastest catalyst was the threonine mutant A3C ((Ac-His-Thr)8(Dap-His-Thr)4(Dap-His-Thr)2Dap-His-Thr-NH2), with kcat = 1.3 min(-1), kcat/k(uncat) = 90'000, KM = 160 microM for 8-bytyryloxypyrene 1,3,6-trisulfonate, corresponding to a rate acceleration of 18'000 per catalytic site and a 5-fold improvement over the original sequence A3.

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

Nature of active tin species and promoting effect of nickle in silica supported tin oxide for dehydrogenation of propane

NASA Astrophysics Data System (ADS)

Wang, Haoren; Wang, Hui; Li, Xiuyi; Li, Chunyi

2017-06-01

Different with Wang et. al.'s study, we found that polymeric Si-O-Sn2+ rather than Ni-Sn alloy and metallic Sn are active species in silica-supported tin oxide catalysts for dehydrogenation of propane. The results showed that high surface area of mesoporous silica brought about high dispersion of tin oxide species, as a result, catalytic activity and stability were both improved. DRUV-vis, XPS, TPR and XRD studies of fresh and reduced catalysts indicated that the deactivation was related to the reduction of active species rather than the coke formation since active tin species cannot maintain its oxidation state at reaction conditions (high temperature and reducing atmosphere). The formed Ni3Sn2 alloy after reduction just functioned as promoter which accelerated the desorption of H2 and regeneration of active site. A synergy effect between active tin species and Ni3Sn2 alloy were observed.

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.

Detection of human Dicer and Argonaute 2 catalytic activity

PubMed Central

Perron, Marjorie P.; Landry, Patricia; Plante, Isabelle; Provost, Patrick

2013-01-01

The microRNA (miRNA)-guided RNA silencing pathway is a central and well-defined cellular process involved in messenger RNA (mRNA) translational control. This complex regulatory process is achieved by a well orchestrated machinery composed of a relatively few protein components, among which the ribonuclease III (RNase III) Dicer and Argonaute 2 (Ago2) play a central role. These two proteins are essential and it is of particular interest to measure and detect their catalytic activity under various situations and/or conditions. In this chapter, we describe different protocols that aim to study and determine the catalytic activity of Dicer and Ago2 in cell extracts, immune complexes and size-fractionated cell extracts. Another protocol aimed at assessing miRNA binding to Ago2 is also described. These experimental approaches are likely to be useful to researchers investigating the main steps of miRNA biogenesis and function in human health and diseases. PMID:21528451

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.

Catalytic activation of carbon-carbon bonds in cyclopentanones.

PubMed

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

2016-11-24

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

Catalytic activation of carbon–carbon bonds in cyclopentanones

PubMed Central

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

2017-01-01

In the chemical industry, molecules of interest are based primarily on carbon skeletons. When synthesizing such molecules, the activation of carbon–carbon single bonds (C–C bonds) in simple substrates is strategically important: it offers a way of disconnecting such inert bonds, forming more active linkages (for example, between carbon and a transition metal) and eventually producing more versatile scaffolds1–13. The challenge in achieving such activation is the kinetic inertness of C–C bonds and the relative weakness of newly formed carbon–metal bonds6,14. The most common tactic starts with a three- or four-membered carbon-ring system9–13, in which strain release provides a crucial thermodynamic driving force. However, broadly useful methods that are based on catalytic activation of unstrained C–C bonds have proven elusive, because the cleavage process is much less energetically favourable. Here we report a general approach to the catalytic activation of C–C bonds in simple cyclopentanones and some cyclohexanones. The key to our success is the combination of a rhodium pre-catalyst, an N-heterocyclic carbene ligand and an amino-pyridine co-catalyst. When an aryl group is present in the C3 position of cyclopentanone, the less strained C–C bond can be activated; this is followed by activation of a carbon–hydrogen bond in the aryl group, leading to efficient synthesis of functionalized α-tetralones—a common structural motif and versatile building block in organic synthesis. Furthermore, this method can substantially enhance the efficiency of the enantioselective synthesis of some natural products of terpenoids. Density functional theory calculations reveal a mechanism involving an intriguing rhodium-bridged bicyclic intermediate. PMID:27806379

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

Rapid enzyme regeneration results in the striking catalytic longevity of an engineered, single species, biocatalytic biofilm.

PubMed

Tong, Xiaoxue; Barberi, Tania Triscari; Botting, Catherine H; Sharma, Sunil V; Simmons, Mark J H; Overton, Tim W; Goss, Rebecca J M

2016-10-21

Engineering of single-species biofilms for enzymatic generation of fine chemicals is attractive. We have recently demonstrated the utility of an engineered Escherichia coli biofilm as a platform for synthesis of 5-halotryptophan. E. coli PHL644, expressing a recombinant tryptophan synthase, was employed to generate a biofilm. Its rapid deposition, and instigation of biofilm formation, was enforced by employing a spin-down method. The biofilm presents a large three-dimensional surface area, excellent for biocatalysis. The catalytic longevity of the engineered biofilm is striking, and we had postulated that this was likely to largely result from protection conferred to recombinant enzymes by biofilm's extracellular matrix. SILAC (stable isotopic labelled amino acids in cell cultures), and in particular dynamic SILAC, in which pulses of different isotopically labelled amino acids are administered to cells over a time course, has been used to follow the fate of proteins. To explore within our spin coated biofilm, whether the recombinant enzyme's longevity might be in part due to its regeneration, we introduced pulses of isotopically labelled lysine and phenylalanine into medium overlaying the biofilm and followed their incorporation over the course of biofilm development. Through SILAC analysis, we reveal that constant and complete regeneration of recombinant enzymes occurs within spin coated biofilms. The striking catalytic longevity within the biofilm results from more than just simple protection of active enzyme by the biofilm and its associated extracellular matrix. The replenishment of recombinant enzyme is likely to contribute significantly to the catalytic longevity observed for the engineered biofilm system. Here we provide the first evidence of a recombinant enzyme's regeneration in an engineered biofilm. The recombinant enzyme was constantly replenished over time as evidenced by dynamic SILAC, which suggests that the engineered E. coli biofilms are highly

Enhanced activity and stability of copper oxide/γ-alumina catalyst in catalytic wet-air oxidation: Critical roles of cerium incorporation

NASA Astrophysics Data System (ADS)

Zhang, Yongli; Zhou, Yanbo; Peng, Chao; Shi, Junjun; Wang, Qingyu; He, Lingfeng; Shi, Liang

2018-04-01

By successive impregnation method, the Ce-modified Cu-O/γ-Al2O3 catalyst was prepared and characterized using nitrogen adsorption-desorption, scanning electron microscopy energy dispersive X-ray analysis (SEM-EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman, and H2-Temperature programming reduction (H2-TPR). In catalytic wet-air oxidation (CWAO) process for the printing and dyeing wastewater (PDW), the effects of Ce addition on performance, mechanism and kinetics of the catalyst were investigated. The Ce addition increases the Brunauer-Emmett-Teller (BET) surface area and pore volume of the catalyst and makes the active components uniformly distributed on the catalyst surface. Formation of a stable CuAl2O4 solid solution by anchoring Cu onto the γ-Al2O3 crystal lattice leads to a significant decrease in metal leaching of the Ce-modified catalyst. The proportion of lattice oxygen in the catalyst substantially increases and the apparent activation energy of Cu-O/γ-Al2O3 catalyst decreases owing to Ce addition. Therefore, the catalytic activity and stability of the Ce-modified catalyst are considerably improved. The scavengers experiments identify the active species existed in the CWAO reaction system, with the order of reactivity: h+ > O2•- > H2O2 > HO•. This novel Cu-Ce-O/γ-Al2O3 catalyst has great potential in applications for treatment of concentrated organic wastewater due to its superior catalytic activity and improved stability.

Direct instrumental identification of catalytically active surface sites

NASA Astrophysics Data System (ADS)

Pfisterer, Jonas H. K.; Liang, Yunchang; Schneider, Oliver; Bandarenka, Aliaksandr S.

2017-09-01

The activity of heterogeneous catalysts—which are involved in some 80 per cent of processes in the chemical and energy industries—is determined by the electronic structure of specific surface sites that offer optimal binding of reaction intermediates. Directly identifying and monitoring these sites during a reaction should therefore provide insight that might aid the targeted development of heterogeneous catalysts and electrocatalysts (those that participate in electrochemical reactions) for practical applications. The invention of the scanning tunnelling microscope (STM) and the electrochemical STM promised to deliver such imaging capabilities, and both have indeed contributed greatly to our atomistic understanding of heterogeneous catalysis. But although the STM has been used to probe and initiate surface reactions, and has even enabled local measurements of reactivity in some systems, it is not generally thought to be suited to the direct identification of catalytically active surface sites under reaction conditions. Here we demonstrate, however, that common STMs can readily map the catalytic activity of surfaces with high spatial resolution: we show that by monitoring relative changes in the tunnelling current noise, active sites can be distinguished in an almost quantitative fashion according to their ability to catalyse the hydrogen-evolution reaction or the oxygen-reduction reaction. These data allow us to evaluate directly the importance and relative contribution to overall catalyst activity of different defects and sites at the boundaries between two materials. With its ability to deliver such information and its ready applicability to different systems, we anticipate that our method will aid the rational design of heterogeneous catalysts.

Physics-based enzyme design: predicting binding affinity and catalytic activity.

PubMed

Sirin, Sarah; Pearlman, David A; Sherman, Woody

2014-12-01

Computational enzyme design is an emerging field that has yielded promising success stories, but where numerous challenges remain. Accurate methods to rapidly evaluate possible enzyme design variants could provide significant value when combined with experimental efforts by reducing the number of variants needed to be synthesized and speeding the time to reach the desired endpoint of the design. To that end, extending our computational methods to model the fundamental physical-chemical principles that regulate activity in a protocol that is automated and accessible to a broad population of enzyme design researchers is essential. Here, we apply a physics-based implicit solvent MM-GBSA scoring approach to enzyme design and benchmark the computational predictions against experimentally determined activities. Specifically, we evaluate the ability of MM-GBSA to predict changes in affinity for a steroid binder protein, catalytic turnover for a Kemp eliminase, and catalytic activity for α-Gliadin peptidase variants. Using the enzyme design framework developed here, we accurately rank the most experimentally active enzyme variants, suggesting that this approach could provide enrichment of active variants in real-world enzyme design applications. © 2014 Wiley Periodicals, Inc.

Ce-Sn binary oxide catalyst for the selective catalytic reduction of NOx by NH3

NASA Astrophysics Data System (ADS)

Liu, Zhiming; Feng, Xu; Zhou, Zizheng; Feng, Yongjun; Li, Junhua

2018-01-01

Ce-Sn binary oxide catalysts prepared by the hydrothermal method have been investigated for the selective catalytic reduction (SCR) of NOx with NH3. Compared with pure CeO2 and SnO2, Ce-Sn binary oxide catalyst showed significantly higher NH3-SCR activity. Moreover, Ce-Sn catalyst showed high resistance against H2O and SO2. The high catalytic performance of Ce-Sn binary oxide is attributed to the synergetic effect between Ce and Sn species, which not only enhances the redox property of the catalyst but also increases the Lewis acidity, thus promoting the adsorption and activation of NH3 species, which contributes to improving the NH3-SCR performance.

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.

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.

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.

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

PubMed Central

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

2017-01-01

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

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.

[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.

Design of activated serine-containing catalytic triads with atomic level accuracy

PubMed Central

Rajagopalan, Sridharan; Wang, Chu; Yu, Kai; Kuzin, Alexandre P.; Richter, Florian; Lew, Scott; Miklos, Aleksandr E.; Matthews, Megan L.; Seetharaman, Jayaraman; Su, Min; Hunt, John. F.; Cravatt, Benjamin F.; Baker, David

2014-01-01

A challenge in the computational design of enzymes is that multiple properties must be simultaneously optimized -- substrate-binding, transition state stabilization, and product release -- and this has limited the absolute activity of successful designs. Here, we focus on a single critical property of many enzymes: the nucleophilicity of an active site residue that initiates catalysis. We design proteins with idealized serine-containing catalytic triads, and assess their nucleophilicity directly in native biological systems using activity-based organophosphate probes. Crystal structures of the most successful designs show unprecedented agreement with computational models, including extensive hydrogen bonding networks between the catalytic triad (or quartet) residues, and mutagenesis experiments demonstrate that these networks are critical for serine activation and organophosphate-reactivity. Following optimization by yeast-display, the designs react with organophosphate probes at rates comparable to natural serine hydrolases. Co-crystal structures with diisopropyl fluorophosphate bound to the serine nucleophile suggest the designs could provide the basis for a new class of organophosphate captures agents. PMID:24705591

Metal Vinylidenes as Catalytic Species in Organic Reactions

PubMed Central

McClory, Andrew

2008-01-01

Organic vinylidene species have found limited use in organic synthesis due to their inaccessibility. In contrast, metal vinylidenes are much more stable, and may be readily accessed through transition metal activation of terminal alkynes. These electrophilic species may be trapped by a number of nucleophiles. Additionally, metal vinylidenes can participate in pericyclic reactions and processes involving migration of a metal ligand to the vinylidene species. This review addresses the reactions and applications of metal vinylidenes in organic synthesis. PMID:18172846

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

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

Curran, Christopher D.; Lu, Li; Jia, Yue

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

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

QM/MM simulations identify the determinants of catalytic activity differences between type II dehydroquinase enzymes.

PubMed

Lence, Emilio; van der Kamp, Marc W; González-Bello, Concepción; Mulholland, Adrian J

2018-05-16

Type II dehydroquinase enzymes (DHQ2), recognized targets for antibiotic drug discovery, show significantly different activities dependent on the species: DHQ2 from Mycobacterium tuberculosis (MtDHQ2) and Helicobacter pylori (HpDHQ2) show a 50-fold difference in catalytic efficiency. Revealing the determinants of this activity difference is important for our understanding of biological catalysis and further offers the potential to contribute to tailoring specificity in drug design. Molecular dynamics simulations using a quantum mechanics/molecular mechanics potential, with correlated ab initio single point corrections, identify and quantify the subtle determinants of the experimentally observed difference in efficiency. The rate-determining step involves the formation of an enolate intermediate: more efficient stabilization of the enolate and transition state of the key step in MtDHQ2, mainly by the essential residues Tyr24 and Arg19, makes it more efficient than HpDHQ2. Further, a water molecule, which is absent in MtDHQ2 but involved in generation of the catalytic Tyr22 tyrosinate in HpDHQ2, was found to destabilize both the transition state and the enolate intermediate. The quantification of the contribution of key residues and water molecules in the rate-determining step of the mechanism also leads to improved understanding of higher potencies and specificity of known inhibitors, which should aid ongoing inhibitor design.

Catalytically active Au-O(OH) x- species stabilized by alkali ions on zeolites and mesoporous oxides

DOE PAGES

Yang, Ming; Li, Sha; Wang, Yuan; ...

2014-11-27

Here we report that the addition of alkali ions (sodium or potassium) to gold on KLTL-zeolite and mesoporous MCM-41 silica stabilizes mononuclear gold in Au-O(OH) x-(Na or K) ensembles. This single-site gold species is active for the low-temperature (<200°C) water-gas shift (WGS) reaction. Unexpectedly, gold is thus similar to platinum in creating –O linkages with more than eight alkali ions and establishing an active site on various supports. The intrinsic activity of the single-site gold species is the same on irreducible supports as on reducible ceria, iron oxide, and titania supports, apparently all sharing a common, similarly structured gold activemore » site. This finding paves the way for using earth-abundant supports to disperse and stabilize precious metal atoms with alkali additives for the WGS and potentially other fuel-processing reactions.« less

Gold-Copper Nanoparticles: Nanostructural Evolution and Bifunctional Catalytic Sites

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

Yin, Jun; Shan, Shiyao; Yang, Lefu

2012-12-12

Understanding of the atomic-scale structure is essential for exploiting the unique catalytic properties of any nanoalloy catalyst. This report describes novel findings of an investigation of the nanoscale alloying of gold-copper (AuCu) nanoparticles and its impact on the surface catalytic functions. Two pathways have been explored for the formation of AuCu nanoparticles of different compositons, including wet chemical synthesis from mixed Au- and Cu-precursor molecules, and nanoscale alloying via an evolution of mixed Au- and Cu-precursor nanoparticles near the nanoscale melting temperatures. For the evolution of mixed precursor nanoparticles, synchrotron x-ray based in-situ real time XRD was used to monitormore » the structural changes, revealing nanoscale alloying and reshaping towards an fcc-type nanoalloy (particle or cube) via a partial melting–resolidification mechanism. The nanoalloys supported on carbon or silica were characterized by in-situ high-energy XRD/PDFs, revealing an intriguing lattice "expanding-shrinking" phenomenon depending on whether the catalyst is thermochemically processed under oxidative or reductive atmosphere. This type of controllable structural changes is found to play an important role in determining the catalytic activity of the catalysts for carbon monoxide oxidation reaction. The tunable catalytic activities of the nanoalloys under thermochemically oxidative and reductive atmospheres are also discussed in terms of the bifunctional sites and the surface oxygenated metal species for carbon monoxide and oxygen activation.« less

In situ formed catalytically active ruthenium nanocatalyst in room temperature dehydrogenation/dehydrocoupling of ammonia-borane from Ru(cod)(cot) precatalyst.

PubMed

Zahmakiran, Mehmet; Ayvalı, Tuğçe; Philippot, Karine

2012-03-20

The development of simply prepared and effective catalytic materials for dehydrocoupling/dehydrogenation of ammonia-borane (AB; NH(3)BH(3)) under mild conditions remains a challenge in the field of hydrogen economy and material science. Reported herein is the discovery of in situ generated ruthenium nanocatalyst as a new catalytic system for this important reaction. They are formed in situ during the dehydrogenation of AB in THF at 25 °C in the absence of any stabilizing agent starting with homogeneous Ru(cod)(cot) precatalyst (cod = 1,5-η(2)-cyclooctadiene; cot = 1,3,5-η(3)-cyclooctatriene). The preliminary characterization of the reaction solutions and the products was done by using ICP-OES, ATR-IR, TEM, XPS, ZC-TEM, GC, EA, and (11)B, (15)N, and (1)H NMR, which reveal that ruthenium nanocatalyst is generated in situ during the dehydrogenation of AB from homogeneous Ru(cod)(cot) precatalyst and B-N polymers formed at the initial stage of the catalytic reaction take part in the stabilization of this ruthenium nanocatalyst. Moreover, following the recently updated approach (Bayram, E.; et al. J. Am. Chem. Soc.2011, 133, 18889) by performing Hg(0), CS(2) poisoning experiments, nanofiltration, time-dependent TEM analyses, and kinetic investigation of active catalyst formation to distinguish single metal or in the present case subnanometer Ru(n) cluster-based catalysis from polymetallic Ru(0)(n) nanoparticle catalysis reveals that in situ formed Ru(n) clusters (not Ru(0)(n) nanoparticles) are kinetically dominant catalytically active species in our catalytic system. The resulting ruthenium catalyst provides 120 total turnovers over 5 h with an initial turnover frequency (TOF) value of 35 h(-1) at room temperature with the generation of more than 1.0 equiv H(2) at the complete conversion of AB to polyaminoborane (PAB; [NH(2)BH(2)](n)) and polyborazylene (PB; [NHBH](n)) units.

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J; Hryn, John N; Elam, Jeffrey W

2013-08-27

A nanoporous catalytic membrane which displays several unique features Including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity. Also provided is a method for producing a catalytic membrane having flow-through pores and discreet catalytic clusters adhering to the inside surfaces of the pores.

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.

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 transfer hydrogenation with terdentate CNN ruthenium complexes: the influence of the base.

PubMed

Baratta, Walter; Siega, Katia; Rigo, Pierluigi

2007-01-01

The catalytic activity of the terdentate complex [RuCl(CNN)(dppb)] (A) [dppb=Ph(2)P(CH(2))(4)PPh(2); HCNN=6-(4'-methylphenyl)-2-pyridylmethylamine] in the transfer hydrogenation of acetophenone (S) with 2-propanol has been found to be dependent on the base concentration. The limit rate has been observed when NaOiPr is used in high excess (A/base molar ratio > 10). The amino-isopropoxide species [Ru(OiPr)(CNN)(dppb)] (B), which forms by reaction of A with sodium isopropoxide via displacement of the chloride, is catalytically active. The rate of conversion of acetophenone obeys second-order kinetics v=k[S][B] with the rate constants in the range 218+/-8 (40 degrees C) to 3000+/-70 M(-1) s(-1) (80 degrees C). The activation parameters, evaluated from the Eyring equation are DeltaH(++)=14.0+/-0.2 kcal mol(-1) and DeltaS(++)=-3.2 +/-0.5 eu. In a pre-equilibrium reaction with 2-propanol complex B gives the cationic species [Ru(CNN)(dppb)(HOiPr)](+)[OiPr](-) (C) with K approximately 2x10(-5) M. The hydride species [RuH(CNN)(dppb)] (H), which forms from B via beta-hydrogen elimination process, catalyzes the reduction of S and, importantly, its activity increases by addition of base. The catalytic behavior of the hydride H has been compared to that of the system A/NaOiPr (1:1 molar ratio) and indicates that the two systems are equivalent.

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

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.

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.

Catalytic Activity of a Binary Informational Macromolecule

NASA Technical Reports Server (NTRS)

Reader, John S.; Joyce, Gerald F.

2003-01-01

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

Evaluation of the Catalytic Activity and Cytotoxicity of Palladium Nanocubes. The Role of Oxygen

PubMed Central

Dahal, Eshan; Curtiss, Jessica; Subedi, Deepak; Chen, Gen; Houston, Jessica P.; Smirnov, Sergei

2015-01-01

Recently it has been reported that palladium nanocubes (PdNC) are capable of generating singlet oxygen without photo-excitation simply via chemisorption of molecular oxygen on its surface. Such a trait would make PdNC a highly versatile catalyst suitable in organic synthesis and a Reactive Oxygen Species (ROS) inducing cancer treatment reagent. Here we thoroughly investigated the catalytic activity of PdNC with respect to their ability to produce singlet oxygen and to oxidize 3,5,3′,5′-tetramethyl-benzidine (TMB), as well as, analyzed the cytotoxic properties of PdNC on HeLa cells. Our findings showed no evidence of singlet oxygen production by PdNC. The nanocubes’ activity is not necessarily linked to activation of oxygen. The oxidation of substrate on PdNC can be a first step followed by PdNC regeneration with oxygen or other oxidant. The catalytic activity of PdNC towards oxidation of TMB is very high and shows direct two-electrons oxidation when the surface of PdNC is clean and the ratio of TMB/PdNC is not very high. Sequential one electron oxidation is observed when the pristine quality of PdNC surface is compromised by serum or uncontrolled impurities and/or the ratio of TMB/PdNC is high. Clean PdNC in serum-free media efficiently induce apoptosis of HeLa cells. It is the primary route of cell death and is associated with hyperpolarization of mitochondria, contrary to a common mitochondrial depolarization initiated by ROS. Again, the effects are very sensitive to how well the pristine surface of PdNC is preserved, suggesting that PdNC can be used as an apoptosis inducing agent but only with appropriate drug delivery system. PMID:25886644

Optical manipulation and catalytic activity enhanced by surface plasmon effect

NASA Astrophysics Data System (ADS)

Zou, Ningmu; Min, Jiang; Jiao, Wenxiang; Wang, Guanghui

2017-02-01

For optical manipulation, a nano-optical conveyor belt consisting of an array of gold plasmonic non-concentric nano-rings (PNNRs) is demonstrated for the realization of trapping and unidirectional transportation of nanoparticles by polarization rotation of excitation beam. These hot spots of an asymmetric plasmonic nanostructure are polarization dependent, therefore, one can use the incident polarization state to manipulate the trapped targets. Trapped particles could be transferred between adjacent PNNRs in a given direction just by rotating the polarization of incident beam due to unbalanced potential. The angular dependent distribution of electric field around PNNR has been solved using the three- dimensional finite-difference time-domain (FDTD) technique. For optical enhanced catalytic activity, the spectral properties of dimers of Au nanorod-Au nanorod nanostructures under the excitation of 532nm photons have been investigated. With a super-resolution catalytic mapping technique, we identified the existence of "hot spot" in terms of catalytic reactivity at the gap region within the twined plasmonic nanostructure. Also, FDTD calculation has revealed an intrinsic correlation between hot electron transfer.

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.

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.

Al-doped TiO{sub 2} mesoporous material supported Pd with enhanced catalytic activity for complete oxidation of ethanol

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

Zhu, Jing, E-mail: mlczjsls123@163.com; Mu, Wentao, E-mail: mwt15035687833@163.com; Su, Liqing, E-mail: suliqing0163@163.com

Pd catalysts supported on Al-doped TiO{sub 2} mesoporous materials were evaluated in complete oxidation of ethanol. The catalysts synthesized by wet impregnation based on evaporation-induced self-assembly were characterized by X-ray diffraction, measurement of pore structure, XPS, FT-IR, temperature programmed reduction and TEM. Characteristic results showed that the aluminium was doped into the lattice of mesoporous anatase TiO{sub 2} to form Al-O-Ti defect structure. Catalytic results revealed that Al-doped catalysts were much more active than the pristine one, especially at low temperature (≤200 °C). This should be ascribed to the introduction of aluminium ions that suppressed the strong metal-support interaction andmore » increased the active sites of Pd oxides, enhanced the stabilized anatase TiO{sub 2}, improved well dispersed high valence palladium species with high reducibility and enriched chemisorption oxygen. - Graphical abstract: Al-doped Pd/TiO{sub 2} exhibited optimal catalytic performance for ethanol oxidation and CO{sub 2} yield by the suppression of SMSI. - Highlights: • Palladium catalysts supported on Al-doped TiO{sub 2} mesoporous materials were studied. • The introduction of Al can enhance anatase stabilization and increase defect TiO{sub 2}. • The Pd/Al-TiO{sub 2} catalysts show higher ethanol conversion and CO{sub 2} yield than Pd/TiO{sub 2}. • The influence of Al on SMSI and catalytic performance were evaluated by TPR and XPS.« less

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.

Catalytically and biologically active silver nanoparticles synthesized using essential oil

NASA Astrophysics Data System (ADS)

Vilas, Vidya; Philip, Daizy; Mathew, Joseph

2014-11-01

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

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

Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

NASA Astrophysics Data System (ADS)

Sherly, K. B.; Rakesh, K.

2014-01-01

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

Synthesis and catalytic activity of polysaccharide templated nanocrystalline sulfated zirconia

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

Sherly, K. B.; Rakesh, K.

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

Cardiac HDAC6 Catalytic Activity is Induced in Response to Chronic Hypertension

PubMed Central

Lemon, Douglas D.; Horn, Todd R.; Cavasin, Maria A.; Jeong, Mark Y.; Haubold, Kurt W.; Long, Carlin S.; Irwin, David C.; McCune, Sylvia A.; Chung, Eunhee; Leinwand, Leslie A.; McKinsey, Timothy A.

2011-01-01

Small molecule histone deacetylase (HDAC) inhibitors block adverse cardiac remodeling in animal models of heart failure. The efficacious compounds target class I, class IIb and, to a lesser extent, class IIa HDACs. It is hypothesized that a selective inhibitor of a specific HDAC class (or an isoform within that class) will provide a favorable therapeutic window for the treatment of heart failure, although the optimal selectivity profile for such a compound remains unknown. Genetic studies have suggested that class I HDACs promote pathological cardiac remodeling, while class IIa HDACs are protective. In contrast, nothing is known about the function or regulation of class IIb HDACs in the heart. We developed assays to quantify catalytic activity of distinct HDAC classes in left and right ventricular cardiac tissue from animal models of hypertensive heart disease. Class I and IIa HDAC activity was elevated in some but not all diseased tissues. In contrast, catalytic activity of the class IIb HDAC, HDAC6, was consistently increased in stressed myocardium, but not in a model of physiologic hypertrophy. HDAC6 catalytic activity was also induced by diverse extracellular stimuli in cultured cardiac myocytes and fibroblasts. These findings suggest an unforeseen role for HDAC6 in the heart, and highlight the need for pre-clinical evaluation of HDAC6-selective inhibitors to determine whether this HDAC isoform is pathological or protective in the setting of cardiovascular disease. PMID:21539845

Identification of an active acidic residue in the catalytic site of beta-hexosaminidase.

PubMed

Tse, R; Vavougios, G; Hou, Y; Mahuran, D J

1996-06-11

Human beta-hexosaminidases A and B (EC 3.2.1.52) are dimeric lysosomal glycosidases composed of evolutionarily related alpha and/or beta subunits. Both isozymes hydrolyze terminal beta-linked GalNAc or GlcNAc residues from numerous artificial and natural substrates; however, in vivo GM2 ganglioside is a substrate for only the heterodimeric A isozyme. Thus, mutations in either gene encoding its alpha or beta subunits can result in GM2 ganglioside storage and Tay-Sachs or Sandhoff disease, respectively. All glycosyl hydrolases ae believed to have one or more acidic residues in their catalytic site. We demonstrate that incubation of hexosaminidase with a chemical modifier specific for carboxyl side chains produces a time-dependent loss of activity, and that this effect can be blocked by the inclusion of a strong competitive inhibitor in the reaction mix. We hypothesized that the catalytic acid residue(s) should be located in a region of overall homology and be invariant within the aligned deduced primary sequences of the human alpha and beta subunits, as well as hexosaminidases from other species, including bacteria. Such a region is encoded by exons 5-6 of the HEXA and HEXB genes. This region includes beta Arg211 (invariant in 15 sequences), which we have previously shown to be an active residue. This region also contains two invariant and one conserved acidic residues. A fourth acidic residue, Asp alpha 258, beta 290, in exon 7 was also investigated because of its association with the B1 variant of Tay-Sachs disease. Conservative substitutions were made at each candidate residue by in vitro mutagenesis of a beta cDNA, followed by cellular expression. Of these, only the beta Asp196Asn substitution decreased the kcat (350-910-fold) without any noticeable effect on the K(m). Mutagenesis of either beta Asp240 or beta Asp290 to Asn decreased kcat by 10- or 1.4-fold but also raised the K(m) of the enzyme 11- of 3-fold, respectively. The above results strongly suggest that

Metal-ligand cooperation in catalytic intramolecular hydroamination: a computational study of iridium-pyrazolato cooperative activation of aminoalkenes.

PubMed

Tobisch, Sven

2012-06-04

The present study comprehensively explores diverse mechanistic pathways for intramolecular hydroamination of prototype 2,2-dimethyl-4-penten-1-amine by Cp*Ir chloropyrazole (1; Cp*=pentamethylcyclopentadienyl) in the presence of KOtBu base with the aid of density functional theory (DFT) calculations. The most accessible mechanistic pathway for catalytic turnover commences from Cp*Ir pyrazolato (Pz) substrate adduct 2⋅S, representing the catalytically competent compound and proceeds via initial electrophilic activation of the olefin C=C bond by the metal centre. It entails 1) facile and reversible anti nucleophilic amine attack on the iridium-olefin linkage; 2) Ir-C bond protonolysis via stepwise transfer of the ammonium N-H proton at the zwitterionic [Cp*IrPz-alkyl] intermediate onto the metal that is linked to turnover-limiting, reductive, cycloamine elimination commencing from a high-energy, metastable [Cp*IrPz-hydrido-alkyl] species; and 3) subsequent facile cycloamine liberation to regenerate the active catalyst species. The amine-iridium bound 2 a⋅S likely corresponds to the catalyst resting state and the catalytic reaction is expected to proceed with a significant primary kinetic isotope. This study unveils the vital role of a supportive hydrogen-bonded network involving suitably aligned β-basic pyrazolato and cycloamido moieties together with an external amine molecule in facilitating metal protonation and reductive elimination. Cooperative hydrogen bonding thus appears pivotal for effective catalysis. The mechanistic scenario is consonant with catalyst performance data and furthermore accounts for the variation in performance for [Cp*IrPz] compounds featuring a β- or γ-basic pyrazolato unit. As far as the route that involves amine N-H bond activation is concerned, a thus far undocumented pathway for concerted amidoalkene → cycloamine conversion through olefin protonation by the pyrazole N-H concurrent with N-C ring closure is disclosed as a

Probing Active Species in the Nanoscale by Combining XAFS and TEM in Operando Conditions

NASA Astrophysics Data System (ADS)

Frenkel, Anatoly

Understanding mechanisms of work in nanoscale systems is often hindered by their inherent complexity and by our inability to identify and characterize their ``active'' sites. In the size range of 1-5nm, they feature a variety of structural motifs, sizes, shapes, compositions, degrees of crystalline order as well as multiple temporal scales. An additional challenge is that only a fraction of them are actors in the catalytic performance, while majority are spectators. Significant progress in developing such tools for studying nanomaterials can be achieved only when active species can be reliably isolated from spectators, and their role in mechanism of work is understood. In our approach the activity of nanomaterial is measured concurrently with other characteristics, obtained by advanced scattering, spectroscopy and imaging methods. In this talk I will demonstrate the application of a microreactor, compatible with electron microscopy and X-ray Absorption Fine Structure spectroscopy probes, for this purpose. I will illustrate its application by our observation of reaction-driven restructuring of Pt catalysts in the size range from single atoms to 3nm in diameter during catalytic hydrogenation of ethylene. We acknowledge support of DOE BES Grant No. DE-FG02- 03ER15476.

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.

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

PubMed

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

2012-06-30

The concern about the fate of pharmaceutical products has raised owing to the increasing contamination of rivers, lakes and groundwater. The aim of this paper is to evaluate two different processes for paracetamol removal. The catalytic wet air oxidation (CWAO) of paracetamol on activated carbon was investigated both as a water treatment technique using an autoclave reactor and as a regenerative treatment of the carbon after adsorption in a sequential fixed bed process. Three activated carbons (ACs) from different source materials were used as catalysts: two microporous basic ACs (S23 and C1) and a meso- and micro-porous acidic one (L27). During the first CWAO experiment the adsorption capacity and catalytic performance of fresh S23 and C1 were higher than those of fresh L27 despite its higher surface area. This situation changed after AC reuse, as finally L27 gave the best results after five CWAO cycles. Respirometry tests with activated sludge revealed that in the studied conditions the use of CWAO enhanced the aerobic biodegradability of the effluent. In the ADOX process L27 also showed better oxidation performances and regeneration efficiency. This different ageing was examined through AC physico-chemical properties. Copyright © 2012 Elsevier B.V. All rights reserved.

Structural Basis for the Catalytic Activity of Human SER/THR Protein Phosphatase-5

NASA Technical Reports Server (NTRS)

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

2004-01-01

Serinekhreonine protein phosphatase-5 (PP5) affects many signaling networks that regulate cell growth. Here we report the 1.6 Angstrom resolution crystal structure of PP5 catalytic domain with metal and phosphate ions in the active site. The structure reveals a mechanism for PPS-mediated catalysis that requires the precise positioning of two metal ions within a conserved Asp(sup 271)-M(sub 1),-M(sub 2)-His(sup 427)-W(sup 2)-His(sup 304)-Asp(sup 274) catalytic motif, and provides a structural basis for the exceptional catalytic proficiency of protein phosphatases placing them among the most powerful catalysts. Resolution of the entire C-terminus revealed a novel subdomain, and the structure of PP5 should aid development of specific inhibitors.

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.

Three critical hydrogen bonds determine the catalytic activity of the Diels–Alderase ribozyme

PubMed Central

Kraut, Stefanie; Bebenroth, Dirk; Nierth, Alexander; Kobitski, Andrei Y.; Nienhaus, G. Ulrich; Jäschke, Andres

2012-01-01

Compared to protein enzymes, our knowledge about how RNA accelerates chemical reactions is rather limited. The crystal structures of a ribozyme that catalyzes Diels–Alder reactions suggest a rich tertiary architecture responsible for catalysis. In this study, we systematically probe the relevance of crystallographically observed ground-state interactions for catalytic function using atomic mutagenesis in combination with various analytical techniques. The largest energetic contribution apparently arises from the precise shape complementarity between transition state and catalytic pocket: A single point mutant that folds correctly into the tertiary structure but lacks one H-bond that normally stabilizes the pocket is completely inactive. In the rate-limiting chemical step, the dienophile is furthermore activated by two weak H-bonds that contribute ∼7–8 kJ/mol to transition state stabilization, as indicated by the 25-fold slower reaction rates of deletion mutants. These H-bonds are also responsible for the tight binding of the Diels–Alder product by the ribozyme that causes product inhibition. For high catalytic activity, the ribozyme requires a fine-tuned balance between rigidity and flexibility that is determined by the combined action of one inter-strand H-bond and one magnesium ion. A sharp 360° turn reminiscent of the T-loop motif observed in tRNA is found to be important for catalytic function. PMID:21976731

The effect of soot on ammonium nitrate species and NO2 selective catalytic reduction over Cu-zeolite catalyst-coated particulate filter.

PubMed

Mihai, Oana; Tamm, Stefanie; Stenfeldt, Marie; Olsson, Louise

2016-02-28

A selective catalytic reduction (SCR)-coated particulate filter was evaluated by means of dynamic tests performed using NH3, NO2, O2 and H2O. The reactions were examined both prior to and after soot removal in order to study the effect of soot on ammonium nitrate formation and decomposition, ammonia storage and NO2 SCR. A slightly larger ammonia storage capacity was observed when soot was present in the sample, which indicated that small amounts of ammonia can adsorb on the soot. Feeding of NO2 and NH3 in the presence of O2 and H2O at low temperature (150, 175 and 200°C) leads to a large formation of ammonium nitrate species and during the subsequent temperature ramp using H2O and argon, a production of nitrous oxides was observed. The N2O formation is often related to ammonium nitrate decomposition, and our results showed that the N2O formation was clearly decreased by the presence of soot. We therefore propose that in the presence of soot, there are fewer ammonium nitrate species on the surface due to the interactions with the soot. Indeed, we do observe CO2 production during the reaction conditions also at 150°C, which shows that there is a reaction with these species and soot. In addition, the conversion of NOx due to NO2 SCR was significantly enhanced in the presence of soot; we attribute this to the smaller amount of ammonium nitrate species present in the experiments where soot is available since it is well known that ammonium nitrate formation is a major problem at low temperature due to the blocking of the catalytic sites. Further, a scanning electron microscopy analysis of the soot particles shows that they are about 30-40 nm and are therefore too large to enter the pores of the zeolites. There are likely CuxOy or other copper species available on the outside of the zeolite crystallites, which could have been enhanced due to the hydrothermal treatment at 850°C of the SCR-coated filter prior to the soot loading. We therefore propose that soot is

Enhancement of Catalytic Activity of Reduced Graphene Oxide Via Transition Metal Doping Strategy

NASA Astrophysics Data System (ADS)

Lee, Hangil; Hong, Jung A.

2017-06-01

To compare the catalytic oxidation activities of reduced graphene oxide (rGO) and rGO samples doped with five different transition metals (TM-rGO), we determine their effects on the oxidation of L-cysteine (Cys) in aqueous solution by performing electrochemistry (EC) measurements and on the photocatalytic oxidation of Cys by using high-resolution photoemission spectroscopy (HRPES) under UV illumination. Our results show that Cr-, Fe-, and Co-doped rGO with 3+ charge states (stable oxide forms: Cr3+, Fe3+, and Co3+) exhibit enhanced catalytic activities that are due to the charge states of the doped metal ions as we compare them with Cr-, Fe-, and Co-doped rGO with 2+ charge states.

Self-propulsion and interactions of catalytic particles in a chemically active medium.

PubMed

Banigan, Edward J; Marko, John F

2016-01-01

Enzymatic "machines," such as catalytic rods or colloids, can self-propel and interact by generating gradients of their substrates. We theoretically investigate the behaviors of such machines in a chemically active environment where their catalytic substrates are continuously synthesized and destroyed, as occurs in living cells. We show how the kinetic properties of the medium modulate self-propulsion and pairwise interactions between machines, with the latter controlled by a tunable characteristic interaction range analogous to the Debye screening length in an electrolytic solution. Finally, we discuss the effective force arising between interacting machines and possible biological applications, such as partitioning of bacterial plasmids.

Tuning the Catalytic Activity of Subcellular Nanoreactors.

PubMed

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

2016-07-31

Bacterial microcompartments are naturally occurring subcellular organelles of bacteria and serve as a promising scaffold for the organization of heterologous biosynthetic pathways. A critical element in the design of custom biosynthetic organelles is quantitative control over the loading of heterologous enzymes to the interior of the organelles. We demonstrate that the loading of heterologous proteins to the 1,2-propanediol utilization microcompartment of Salmonella enterica can be controlled using two strategies: by modulating the transcriptional activation of the microcompartment container and by coordinating the expression of the microcompartment container and the heterologous cargo. These strategies allow general control over the loading of heterologous proteins localized by two different N-terminal targeting peptides and represent an important step toward tuning the catalytic activity of bacterial microcompartments for increased biosynthetic productivity. Copyright © 2016. Published by Elsevier Ltd.

Catalytic nanoporous membranes

DOEpatents

Pellin, Michael J [Naperville, IL; Hryn, John N [Naperville, IL; Elam, Jeffrey W [Elmhurst, IL

2009-12-01

A nanoporous catalytic membrane which displays several unique features including pores which can go through the entire thickness of the membrane. The membrane has a higher catalytic and product selectivity than conventional catalysts. Anodic aluminum oxide (AAO) membranes serve as the catalyst substrate. This substrate is then subjected to Atomic Layer Deposition (ALD), which allows the controlled narrowing of the pores from 40 nm to 10 nm in the substrate by deposition of a preparatory material. Subsequent deposition of a catalytic layer on the inner surfaces of the pores reduces pore sizes to less than 10 nm and allows for a higher degree of reaction selectivity. The small pore sizes allow control over which molecules enter the pores, and the flow-through feature can allow for partial oxidation of reactant species as opposed to complete oxidation. A nanoporous separation membrane, produced by ALD is also provided for use in gaseous and liquid separations. The membrane has a high flow rate of material with 100% selectivity.

Catalytically active nanorotor reversibly self-assembled by chemical signaling within an eight-component network.

PubMed

Goswami, Abir; Pramanik, Susnata; Schmittel, Michael

2018-04-17

A catalytically active three-component nanorotor is reversibly self-assembled and disassembled by remote control. When zinc(ii) ions (2 equiv.) are added as an external chemical trigger to the mixture of transmitter [Cu(1)]+ and pre-rotor assembly [(S)·(R)], two equiv. of copper(i) ions translocate from [Cu(1)]+ to the two phenanthroline sites of [(S)·(R)]. As a result, [Zn(1)]2+ forms along with the three-component assembly [Cu2(S)(R)]2+, which is both a nanorotor (k298 = 46 kHz, ΔH‡ = 49.1 ± 0.4 kJ mol-1, ΔS‡ = 9.5 ± 1.7 J mol-1 K-1) and a catalyst for click reactions (catalysis ON: A + B→AB). Removal of zinc from the mixture reverts the translocation sequence and thus commands disassembly of the catalytically active rotor (catalysis OFF). The ON/OFF catalytic cycle was run twice in situ in the full network.

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

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.

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.

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.

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.

Bioinspired catalytic generation of high-valent cobalt-oxo species by the axially coordinated CoPc on pyridine-functionalized MWCNTs for the elimination of organic contaminants

NASA Astrophysics Data System (ADS)

Li, Nan; Wang, Ying; Wu, Chenren; Lu, Wangyang; Pei, Kemei; Chen, Wenxing

2018-03-01

Enzymes have always been a source of inspiration for the design and improvement of catalysts. Many examples are occurring in heme/non-heme metalloenzymes with the generation of active high-valent metal-oxo intermediates that are controlled by the surrounding amino acids/protein and axial residue ligands, facilitating the efficient oxidation of substrates in biochemical processes. Here, the high-valent cobalt-oxo species have been formed during the heterolysis of H2O2 activated by the bioinspired catalyst, axially coordinated cobalt phthalocyanine (CoPc) on pyridine-functionalized multi-walled carbon nanotubes (MWCNTs-Py), characterized by ultraviolet-visible and X-ray photoelectron spectroscopy. Formation process of the active cobalt-oxo species has been further confirmed by electrospray ionization mass spectrometry analysis and the results from the density functional theory (B3LYP/6-311G) calculations. Such high-valent cobalt-oxo species exhibit high reactivity and enough persistence for the oxidation of the target substrate, C.I. Acid Red 1. The oxidation products are nearly biodegradable small molecules identified by ultra-performance liquid chromatography/high-definition mass spectrometry. This strategy provides a foundation on developing efficient and persistent catalytic system, in particular oxidation processes based on the complex catalysts with N4 macrocycle structures.

Enhancement of catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol through interfacial modification with heteropolymolybdates

NASA Astrophysics Data System (ADS)

Barczuk, Piotr J.; Lewera, Adam; Miecznikowski, Krzysztof; Zurowski, Artur; Kulesza, Pawel J.

As evidenced from the increase of electrocatalytic currents measured under voltammetric and chronoamperometric conditions, the activity of bimetallic Pt-Ru and Pt-Sn nanoparticles towards oxidation of ethanol is increased by modification of their surfaces with ultra-thin films of phosphododecamolybdic acid (H 3PMo 12O 40). The enhancement effect has been most pronounced in a case of heteropolymolybdate-modified carbon-supported Pt-Sn catalysts. Independent high-resolution XPS measurements indicate the ability of heteropolymolybdates to stabilize tin (in bimetallic Pt-Sn particles) at higher oxidation states (presumably as tin oxo species). The overall activation effect may also be ascribed to changes in the morphology of catalytic films following modification with heteropolymolybdates. Presence of the polyoxometallate is also likely to increase of the interfacial population of reactive oxo groups in the vicinity of platinum centers.

Anchoring and promotion effects of metal oxides on silica supported catalytic gold nanoparticles.

PubMed

Luo, Jingjie; Ersen, Ovidiu; Chu, Wei; Dintzer, Thierry; Petit, Pierre; Petit, Corinne

2016-11-15

The understanding of the interactions between the different components of supported metal doped gold catalysts is of crucial importance for selecting and designing efficient gold catalysts for reactions such as CO oxidation. To progress in this direction, a unique supported nano gold catalyst Au/SS was prepared, and three doped samples (Au/SS@M) were elaborated. The samples before and after test were characterized by Transmission Electron Microscopy (TEM) and X-ray Photoelectron Spectroscopy (XPS). It is found that the doping metal species prefer to be located on the surface of gold nanoparticles and that a small amount of additional reductive metal leads to more efficient reaction. During the catalytic test, the nano-structure of the metal species transforms depending on its chemical nature. This study allows one to identify and address the contribution of each metal on the CO reaction in regard to oxidative species of gold, silica and dopants. Metal doping leads to different exposure of interface sites between Au and metal oxide, which is one of the key factors for the change of the catalytic activity. The metal oxides help the activation of oxygen by two actions: mobility inside the metal bulk and transfer of water species onto of gold nanoparticles. Copyright © 2016. Published by Elsevier Inc.

Ferredoxin-thioredoxin reductase: a catalytically active dithiol group links photoreduced ferredoxin to thioredoxin functional in photosynthetic enzyme regulation.

PubMed

Droux, M; Miginiac-Maslow, M; Jacquot, J P; Gadal, P; Crawford, N A; Kosower, N S; Buchanan, B B

1987-07-01

The mechanism by which the ferredoxin-thioredoxin system activates the target enzyme, NADP-malate dehydrogenase, was investigated by analyzing the sulfhydryl status of individual protein components with [14C]iodoacetate and monobromobimane. The data indicate that ferredoxin-thioredoxin reductase (FTR)--an iron-sulfur enzyme present in oxygenic photosynthetic organisms--is the first member of a thiol chain that links light to enzyme regulation. FTR possesses a catalytically active dithiol group localized on the 13 kDa (similar) subunit, that occurs in all species investigated and accepts reducing equivalents from photoreduced ferredoxin and transfers them stoichiometrically to the disulfide form of thioredoxin m. The reduced thioredoxin m, in turn, reduces NADP-malate dehydrogenase, thereby converting it from an inactive (S-S) to an active (SH) form. The means by which FTR is able to combine electrons (from photoreduced ferredoxin) with protons (from the medium) to reduce its active disulfide group remains to be determined.

Ferredoxin-thioredoxin reductase: a catalytically active dithiol group links photoreduced ferredoxin to thioredoxin functional in photosynthetic enzyme regulation

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

Droux, M.; Miginiac-Maslow, M.; Jacquot, J.P.

The mechanism by which the ferredoxin-thioredoxin system activates the target enzyme, NADP-malate dehydrogenase, was investigated by analyzing the sulfhydryl status of individual protein components with (/sup 14/C)iodoacetate and monobromobimane. The data indicate that ferredoxin-thioredoxin reductase (FTR)--an iron-sulfur enzyme present in oxygenic photosynthetic organisms--is the first member of a thiol chain that links light to enzyme regulation. FTR possesses a catalytically active dithiol group localized on the 13 kDa (similar) subunit, that occurs in all species investigated and accepts reducing equivalents from photoreduced ferredoxin and transfers them stoichiometrically to the disulfide form of thioredoxin m. The reduced thioredoxin m, in turn,more » reduces NADP-malate dehydrogenase, thereby converting it from an inactive (S-S) to an active (SH) form. The means by which FTR is able to combine electrons (from photoreduced ferredoxin) with protons (from the medium) to reduce its active disulfide group remains to be determined.« less

Direct Visualization of Catalytically Active Sites at the FeO–Pt(111) Interface

DOE PAGES

Kudernatsch, Wilhelmine; Peng, Guowen; Zeuthen, Helene; ...

2015-05-31

Within the area of surface science, one of the “holy grails” is to directly visualize a chemical reaction at the atomic scale. Whereas this goal has been reached by high-resolution scanning tunneling microscopy (STM) in a number of cases for reactions occurring at flat surfaces, such a direct view is often inhibited for reaction occurring at steps and interfaces. Here we have studied the CO oxidation reaction at the interface between ultrathin FeO islands and a Pt(111) support by in situ STM and density functional theory (DFT) calculations. Time-lapsed STM imaging on this inverse model catalyst in O 2 andmore » CO environments revealed catalytic activity occurring at the FeO–Pt(111) interface and directly showed that the Fe-edges host the catalytically most active sites for the CO oxidation reaction. This is an important result since previous evidence for the catalytic activity of the FeO–Pt(111) interface is essentially based on averaging techniques in conjunction with DFT calculations. As a result, the presented STM results are in accord with DFT+U calculations, in which we compare possible CO oxidation pathways on oxidized Fe-edges and O-edges. We found that the CO oxidation reaction is more favorable on the oxidized Fe-edges, both thermodynamically and kinetically.« less

Application of surface modified nano ferrite nickel in catalytic reaction (epoxidation of alkenes) and investigation on its antibacterial and antifungal activities.

PubMed

Golkhatmi, Faezeh Mahdinejad; Bahramian, Bahram; Mamarabadi, Mojtaba

2017-09-01

Newly, magnetic nanoparticles have extensively been used as alternative catalyst supports, in the view of their high surface area which results in high catalyst loading capacity, high dispersion, low toxicity, environmental preservation, distinguished stability, and suitable catalyst reusing. In the present study, the magnetite nanoparticles, NiFe 2 O 4 @Ag and NiFe 2 O 4 @Mo, were synthesized and characterized. The antimicrobial activities and catalytic properties of synthesized nanoparticles were tested afterwards. For synthetizing the nanoparticle NiFe 2 O 4 @Ag, silver ions were loaded onto the surface of the modified NiFe 2 O 4 and reduced to silver crystal by adding NaBH 4 . The antibacterial effects of NiFe 2 O 4 @Ag were examined against two species of soil and plant related bacteria named Bacillus subtilis (gram positive) and Pseudomonas syringae (gram negative), respectively. The antifungal activity of this nanoparticle was evaluated against two species of plant pathogenic fungi called Alternaria solani and Fusarium oxysporum. Biological results indicated that the synthesized material has shown an excellent antibacterial and antifungal activity against all examined bacteria and fungi so that, their growth were completely inhibited 24h after treatment with NiFe 2 O 4 @Ag. For the synthesis of a heterogeneous catalyst NiFe 2 O 4 @Mo, complex Mo(CO) 6 was loaded onto the surface of the modified NiFe 2 O 4 nanoparticle. This catalyst was found as an efficient catalyst for epoxidation of cis-cyclooctene and a wide variety of alkenes, including aromatic and aliphatic terminal ones using tert-butyl hydroperoxide as oxidant. This new heterogenized catalyst could easily be recovered by using a magnetic separator and reused four consecutive and loss only 13% of its catalytic activity. Copyright © 2017 Elsevier B.V. All rights reserved.

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

Triblock copolymer-mediated synthesis of catalytically active gold nanostructures

NASA Astrophysics Data System (ADS)

Santos, Douglas C.; de Souza, Viviane C.; Vasconcelos, Diego A.; Andrade, George R. S.; Gimenez, Iara F.; Teixeira, Zaine

2018-04-01

The design of nanostructures based on poly(ethylene oxide)-poly(propylene)-poly(ethylene oxide) (PEO-PPO-PEO) and metal nanoparticles is becoming an important research topic due to their multiple functionalities in different fields, including nanomedicine and catalysis. In this work, water-soluble gold nanoparticles have been prepared through a green aqueous synthesis method using Pluronic F127 as both reducing and stabilizing agents. The size dependence (varying from 2 to 70 nm) and stability of gold nanoparticles were systematically studied by varying some parameters of synthesis, which were the polymer concentration, temperature, and exposure to UV-A light, being monitored by UV-Vis spectroscopy and TEM. Also, an elaborated study regarding to the kinetic of formation (nucleation and growth) was presented. Finally, the as-prepared Pluronic-capped gold nanoparticles have shown excellent catalytic activity towards the reduction of 4-nitrophenol to 4-aminophenol with sodium borohydride, in which a higher catalytic performance was exhibited when compared with gold nanoparticles prepared by classical reduction method using sodium citrate. [Figure not available: see fulltext.

Cyclooxygenase-2 inhibitors modulate skin aging in a catalytic activity-independent manner

PubMed Central

Lee, Mi Eun; Kim, So Ra; Lee, Seungkoo; Jung, Yu-Jin; Choi, Sun Shim; Kim, Woo Jin

2012-01-01

It has been proposed that the pro-inflammatory catalytic activity of cyclooxygenase-2 (COX-2) plays a key role in the aging process. However, it remains unclear whether the COX-2 activity is a causal factor for aging and whether COX-2 inhibitors could prevent aging. We here examined the effect of COX-2 inhibitors on aging in the intrinsic skin aging model of hairless mice. We observed that among two selective COX-2 inhibitors and one non-selective COX inhibitor studied, only NS-398 inhibited skin aging, while celecoxib and aspirin accelerated skin aging. In addition, NS-398 reduced the expression of p53 and p16, whereas celecoxib and aspirin enhanced their expression. We also found that the aging-modulating effect of the inhibitors is closely associated with the expression of type I procollagen and caveolin-1. These results suggest that pro-inflammatory catalytic activity of COX-2 is not a causal factor for aging at least in skin and that COX-2 inhibitors might modulate skin aging by regulating the expression of type I procollagen and caveolin-1. PMID:22771771

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 %).

Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells

PubMed Central

Kramm, Ulrike I.; Herranz, Juan; Larouche, Nicholas; Arruda, Thomas M.; Lefèvre, Michel; Jaouen, Frédéric; Bogdanoff, Peter; Fiechter, Sebastian; Abs-Wurmbach, Irmgard; Mukerjee, Sanjeev; Dodelet, Jean-Pol

2012-01-01

Fe-based catalytic sites for the reduction of oxygen in acidic medium have been identified by 57Fe Mössbauer spectroscopy of Fe/N/C catalysts containing 0.03 to 1.55 wt% Fe, which were prepared by impregnation of iron acetate on carbon black followed by heat-treatment in NH3 at 950°C. Four different Fe-species were detected at all iron concentrations: three doublets assigned to molecular FeN4-like sites with their ferrous ion in low (D1), medium (D2) or high spin state (D3), and two other doublets assigned to a single Fe-species (D4 and D5) consisting of surface oxidized nitride nanoparticles (FexN, with x≤2.1). A fifth Fe-species appears only in those catalysts with Fe-contents ≥ 0.27 wt%. It is characterized by a very broad singlet, which has been assigned to incomplete FeN4-like sites that quickly dissolve in contact with an acid. Among the five Fe-species identified in these catalysts, only D1 and D3 display catalytic activity for the oxygen reduction reaction (ORR) in the acid medium, with D3 featuring a composite structure with a protonated neighbour basic nitrogen and being by far the most active species, with an estimated turn over frequency for the ORR of 11.4 e− site−1 s−1 at 0.8V vs RHE. Moreover, all D1 sites and between 1/2 to 2/3 of the D3 sites are acid-resistant. A scheme for the mechanism of site formation upon heat-treatment is also proposed. This identification of the ORR-active sites in these catalysts is of crucial importance to design strategies to improve the catalytic activity and stability of these materials. PMID:22824866

Structure of the catalytic sites in Fe/N/C-catalysts for O2-reduction in PEM fuel cells.

PubMed

Kramm, Ulrike I; Herranz, Juan; Larouche, Nicholas; Arruda, Thomas M; Lefèvre, Michel; Jaouen, Frédéric; Bogdanoff, Peter; Fiechter, Sebastian; Abs-Wurmbach, Irmgard; Mukerjee, Sanjeev; Dodelet, Jean-Pol

2012-09-07

Fe-based catalytic sites for the reduction of oxygen in acidic medium have been identified by (57)Fe Mössbauer spectroscopy of Fe/N/C catalysts containing 0.03 to 1.55 wt% Fe, which were prepared by impregnation of iron acetate on carbon black followed by heat-treatment in NH(3) at 950 °C. Four different Fe-species were detected at all iron concentrations: three doublets assigned to molecular FeN(4)-like sites with their ferrous ions in a low (D1), intermediate (D2) or high (D3) spin state, and two other doublets assigned to a single Fe-species (D4 and D5) consisting of surface oxidized nitride nanoparticles (Fe(x)N, with x≤ 2.1). A fifth Fe-species appears only in those catalysts with Fe-contents ≥0.27 wt%. It is characterized by a very broad singlet, which has been assigned to incomplete FeN(4)-like sites that quickly dissolve in contact with an acid. Among the five Fe-species identified in these catalysts, only D1 and D3 display catalytic activity for the oxygen reduction reaction (ORR) in the acid medium, with D3 featuring a composite structure with a protonated neighbour basic nitrogen and being by far the most active species, with an estimated turn over frequency for the ORR of 11.4 e(-) per site per s at 0.8 V vs. RHE. Moreover, all D1 sites and between 1/2 and 2/3 of the D3 sites are acid-resistant. A scheme for the mechanism of site formation upon heat-treatment is also proposed. This identification of the ORR-active sites in these catalysts is of crucial importance to design strategies to improve the catalytic activity and stability of these materials.

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

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

Al-Ghamdi, Attieh A.; Abdel-wahab, M. Sh., E-mail: mshabaan90@yahoo.com; Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Sciences, Beni-Suef University, Beni-Suef

2016-03-15

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

Real-Time Visualization of Active Species in a Single-Site Metal–Organic Framework Photocatalyst

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

Yang, Sizhuo; Pattengale, Brian; Lee, Sungsik

In this work, we report a new single-site photocatalyst (Co-Ru-UIO- 67(bpy)) based on a metal-organic framework platform with incorporated molecular photosensitizer and catalyst. We show that this catalyst not only demonstrates exceptional activity for light-driven H2 production but also can be recycled without loss of activity. Using the combination of optical transient absorption spectroscopy and in situ X-ray absorption spectroscopy, we not only captured the key CoI intermediate species formed after ultrafast charge transfer from the incorporated photosensitizer but also identified the rate-limiting step in the catalytic cycle, providing insight into the catalysis mechanism of these single-site metal-organic framework photocatalysts.

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.

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

PubMed Central

Wang, Yang-Gang; Mei, Donghai; Glezakou, Vassiliki-Alexandra; Li, Jun; Rousseau, Roger

2015-01-01

Catalysis by gold supported on reducible oxides has been extensively studied, yet issues such as the nature of the catalytic site and the role of the reducible support remain fiercely debated topics. Here we present ab initio molecular dynamics simulations of an unprecedented dynamic single-atom catalytic mechanism for the oxidation of carbon monoxide by ceria-supported gold clusters. The reported dynamic single-atom catalytic mechanism results from the ability of the gold cation to strongly couple with the redox properties of the ceria in a synergistic manner, thereby lowering the energy of redox reactions. The gold cation can break away from the gold nanoparticle to catalyse carbon monoxide oxidation, adjacent to the metal/oxide interface and subsequently reintegrate back into the nanoparticle after the reaction is completed. Our study highlights the importance of the dynamic creation of active sites under reaction conditions and their essential role in catalysis. PMID:25735407

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.

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.

Mechanistic insight into the hydrazine decomposition on Rh(111): effect of reaction intermediate on catalytic activity.

PubMed

Deng, Zhigang; Lu, Xiaoqing; Wen, Zengqiang; Wei, Shuxian; Liu, Yunjie; Fu, Dianling; Zhao, Lianming; Guo, Wenyue

2013-10-14

Periodic density functional theory (DFT) calculations have been performed to systematically investigate the effect of reaction intermediate on catalytic activity for hydrazine (N2H4) decomposition on Rh(111). Reaction mechanisms via intramolecular and NH2-assisted N2H4 decompositions are comparatively analyzed, including adsorption configuration, reaction energy and barrier of elementary step, and reaction network. Our results show that the most favorable N2H4 decomposition pathway starts with the initial N-N bond scission to the NH2 intermediate, followed by stepwise H stripping from adsorbed N2Hx (x = 1-4) species, and finally forms the N2 and NH3 products. Comparatively, the stepwise intramolecular dehydrogenation via N2H4→ N2H3→ N2H2→ N2H → N2, and N2H4→ NH2→ NH → N with or without NH2 promotion effect, are unfavorable due to higher energy barriers encountered. Energy barrier analysis, reaction rate constants, and electronic structures are used to identify the crucial competitive route. The promotion effect of the NH2 intermediate is structurally reflected in the weakening of the N-H bond and strengthening of the N-N bond in N2Hx in the coadsorption system; it results intrinsically from the less structural deformation of the adsorbate, and weakening of the interaction between dehydrogenated fragment and departing H in transition state. Our results highlight the crucial effect of reaction intermediate on catalytic activity and provide a theoretical approach to analyze the effect.

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

PubMed

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

2015-12-02

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

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.

Enhanced room-temperature catalytic decomposition of formaldehyde on magnesium-aluminum hydrotalcite/boehmite supported platinum nanoparticles catalyst.

PubMed

Yan, Zhaoxiong; Yang, Zhihua; Xu, Zhihua; An, Liang; Xie, Fang; Liu, Jiyan

2018-08-15

Magnesium-aluminum hydrotalcite (Mg-Al HT)/boehmite (AlOOH) composite supported Pt catalysts were obtained via one-pot microemulsion synthesis of Mg-Al HT/AlOOH composite and NaBH 4 -reduction of Pt precursor processes. The catalytic performances of the catalysts were evaluated for formaldehyde (HCHO) removal at room temperature. The performance tests showed that the catalyst obtained by immobilizing Pt nanoparticles (NPs) on Mg-Al HT/AlOOH support with Al/Mg molar ratio equivalent to 9:1 (Pt/Al 9 Mg 1 ) displayed a superior catalytic activity and stability for HCHO removal. In order to find out the causes of its higher activity, X-ray diffraction, transmission electron microscopy, N 2 adsorption/desorption, X-ray photoelectron spectroscopy, temperature programmed desorption of CO 2 and reduction of H 2 were used to analyze the physicochemical properties of Pt/Al 9 Mg 1 and Pt/AlOOH. The remarkable catalytic performance of Pt/Al 9 Mg 1 is mainly attributed to the relatively larger amount of surface oxygen species, and more reactive oxygen species led by the interaction of Mg-Al HT and AlOOH/Pt, and relatively larger number of weak base sites caused by Mg-Al HT. The formate species are the main reaction intermediate over Pt/Al 9 Mg 1 during HCHO oxidation at room temperature, which could be further oxidized into CO 2 and H 2 O in the presence of O 2 . This study might shed some light on further improving the catalytic performance of the catalyst for indoor air purification at room temperature. Copyright © 2018 Elsevier Inc. All rights reserved.

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

PubMed

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

2016-04-01

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

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.

Role of coupled dynamics in the catalytic activity of prokaryotic-like prolyl-tRNA synthetases.

PubMed

Sanford, Brianne; Cao, Bach; Johnson, James M; Zimmerman, Kurt; Strom, Alexander M; Mueller, Robyn M; Bhattacharyya, Sudeep; Musier-Forsyth, Karin; Hati, Sanchita

2012-03-13

Prolyl-tRNA synthetases (ProRSs) have been shown to activate both cognate and some noncognate amino acids and attach them to specific tRNA(Pro) substrates. For example, alanine, which is smaller than cognate proline, is misactivated by Escherichia coli ProRS. Mischarged Ala-tRNA(Pro) is hydrolyzed by an editing domain (INS) that is distinct from the activation domain. It was previously shown that deletion of the INS greatly reduced cognate proline activation efficiency. In this study, experimental and computational approaches were used to test the hypothesis that deletion of the INS alters the internal protein dynamics leading to reduced catalytic function. Kinetic studies with two ProRS variants, G217A and E218A, revealed decreased amino acid activation efficiency. Molecular dynamics studies showed motional coupling between the INS and protein segments containing the catalytically important proline-binding loop (PBL, residues 199-206). In particular, the complete deletion of INS, as well as mutation of G217 or E218 to alanine, exhibited significant effects on the motion of the PBL. The presence of coupled dynamics between neighboring protein segments was also observed through in silico mutations and essential dynamics analysis. Altogether, this study demonstrates that structural elements at the editing domain-activation domain interface participate in coupled motions that facilitate amino acid binding and catalysis by bacterial ProRSs, which may explain why truncated or defunct editing domains have been maintained in some systems, despite the lack of catalytic activity.

Catalytic activity of CuOn-La2O3/gamma-Al2O3 for microwave assisted ClO2 catalytic oxidation of phenol wastewater.

PubMed

Bi, Xiaoyi; Wang, Peng; Jiang, Hong

2008-06-15

In order to develop a catalyst with high activity and stability for microwave assisted ClO2 catalytic oxidation, we prepared CuOn-La2O3/gamma-Al2O3 by impregnation-deposition method, and determined its properties using BET, XRF, XPS and chemical analysis techniques. The test results show that, better thermal ability of gamma-Al2O3 and high loading of Cu in the catalyst can be achieved by adding La2O3. The microwave assisted ClO2 catalytic oxidation process with CuOn-La2O3/gamma-Al2O3 used as catalyst was also investigated, and the results show that the catalyst has an excellent catalytic activity in treating synthetic wastewater containing 100 mg/L phenol, and 91.66% of phenol and 50.35% of total organic carbon (TOC) can be removed under the optimum process conditions. Compared with no catalyst process, CuOn-La2O3/gamma-Al2O3 can effectively degrade contaminants in short reaction time and with low oxidant dosage, extensive pH range. The comparison of phenol removal efficiency in the different process indicates that microwave irradiation and catalyst work together to oxidize phenol effectively. It can therefore be concluded from results and discussion that CuOn-La2O3/gamma-Al2O3 is a suitable catalyst in microwave assisted ClO2 catalytic oxidation process.

Molecular catalytic coal liquid conversion

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

Stock, L.M.; Yang, Shiyong

1995-12-31

This research, which is relevant to the development of new catalytic systems for the improvement of the quality of coal liquids by the addition of dihydrogen, is divided into two tasks. Task 1 centers on the activation of dihydrogen by molecular basic reagents such as hydroxide ion to convert it into a reactive adduct (OH{center_dot}H{sub 2}){sup {minus}} that can reduce organic molecules. Such species should be robust withstanding severe conditions and chemical poisons. Task 2 is focused on an entirely different approach that exploits molecular catalysts, derived from organometallic compounds that are capable of reducing monocyclic aromatic compounds under verymore » mild conditions. Accomplishments and conclusions are discussed.« less

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

Catalytic oxidation of low-concentration CO at ambient temperature over supported Pd-Cu catalysts.

PubMed

Wang, Fagen; Zhang, Haojie; He, Dannong

2014-01-01

The CO catalytic oxidation at ambient temperature and high space velocity was studied over the Pd-Cu/MOx (MOx = TiO2 and AI203) catalysts. The higher Brunauer-Emmett-Teller area surface of the A1203 support facilitates the dispersion of Pd2+ species, and the presence of Cu2Cl(OH)3 accelerates the re-oxidation of Pd0 to Pd2+ over the Pd-Cu/Al203 catalyst, which contributed to better performance of CO catalytic oxidation. The poorer activity of the Pd-Cu/TiO2 catalyst was attributed to the lower dispersion of Pd2+ species because of the less surface area and the non-formation of Cu2CI(OH)3 species. The presence of saturated moisture showed a negative effect on CO conversion over the two catalysts. This might be because of the competitive adsorption, the formation of carbonate species and the transformation of Cu2CI(OH)3 to inactive CuCI over the Pd-Cu/AI2O3 catalyst, which facilitates the aggregation of PdO species over the Pd-Cu/TiO2 catalyst under the moisture condition.

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.

Catalytic conversion of light alkanes: Quarterly report, January 1-March 31, 1992

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

Biscardi, J.; Bowden, P.T.; Durante, V.A.

The first Quarterly Report of 1992 on the Catalytic Conversion of Light Alkanes reviews the work done between January 1. 1992 and March 31, 1992 on the Cooperative Agreement. The mission of this work is to devise a new catalyst which can be used in a simple economic process to convert the light alkanes in natural gas to oxygenate products which can either be used as clean-burning, high octane liquid fuels, as fuel components or as precursors to liquid hydrocarbon transportation fuel. During the past quarter we have continued to design, prepare, characterize and test novel catalysts for the mildmore » selective reaction of light hydrocarbons with air or oxygen to produce alcohols directly. These catalysts are designed to form active metal oxo (MO) species and to be uniquely active for the homolytic cleavage of the carbon-hydrogen bonds in light alkanes producing intermediates which can form alcohols. We continue to investigate three molecular environments for the active catalytic species that we are trying to generate: electron-deficient porphryinic macrocycles (PHASE I), polyoxometallates (PHASE II), and regular oxidic lattices including zeolites and related structures as well as other molecular surface structures having metal oxo groups (PHASE III).« less

An active site rearrangement within the Tetrahymena group I ribozyme releases nonproductive interactions and allows formation of catalytic interactions

PubMed Central

Sengupta, Raghuvir N.; Van Schie, Sabine N.S.; Giambaşu, George; Dai, Qing; Yesselman, Joseph D.; York, Darrin; Piccirilli, Joseph A.; Herschlag, Daniel

2016-01-01

Biological catalysis hinges on the precise structural integrity of an active site that binds and transforms its substrates and meeting this requirement presents a unique challenge for RNA enzymes. Functional RNAs, including ribozymes, fold into their active conformations within rugged energy landscapes that often contain misfolded conformers. Here we uncover and characterize one such “off-pathway” species within an active site after overall folding of the ribozyme is complete. The Tetrahymena group I ribozyme (E) catalyzes cleavage of an oligonucleotide substrate (S) by an exogenous guanosine (G) cofactor. We tested whether specific catalytic interactions with G are present in the preceding E•S•G and E•G ground-state complexes. We monitored interactions with G via the effects of 2′- and 3′-deoxy (–H) and −amino (–NH2) substitutions on G binding. These and prior results reveal that G is bound in an inactive configuration within E•G, with the nucleophilic 3′-OH making a nonproductive interaction with an active site metal ion termed MA and with the adjacent 2′-OH making no interaction. Upon S binding, a rearrangement occurs that allows both –OH groups to contact a different active site metal ion, termed MC, to make what are likely to be their catalytic interactions. The reactive phosphoryl group on S promotes this change, presumably by repositioning the metal ions with respect to G. This conformational transition demonstrates local rearrangements within an otherwise folded RNA, underscoring RNA's difficulty in specifying a unique conformation and highlighting Nature's potential to use local transitions of RNA in complex function. PMID:26567314

An active site rearrangement within the Tetrahymena group I ribozyme releases nonproductive interactions and allows formation of catalytic interactions.

PubMed

Sengupta, Raghuvir N; Van Schie, Sabine N S; Giambaşu, George; Dai, Qing; Yesselman, Joseph D; York, Darrin; Piccirilli, Joseph A; Herschlag, Daniel

2016-01-01

Biological catalysis hinges on the precise structural integrity of an active site that binds and transforms its substrates and meeting this requirement presents a unique challenge for RNA enzymes. Functional RNAs, including ribozymes, fold into their active conformations within rugged energy landscapes that often contain misfolded conformers. Here we uncover and characterize one such "off-pathway" species within an active site after overall folding of the ribozyme is complete. The Tetrahymena group I ribozyme (E) catalyzes cleavage of an oligonucleotide substrate (S) by an exogenous guanosine (G) cofactor. We tested whether specific catalytic interactions with G are present in the preceding E•S•G and E•G ground-state complexes. We monitored interactions with G via the effects of 2'- and 3'-deoxy (-H) and -amino (-NH(2)) substitutions on G binding. These and prior results reveal that G is bound in an inactive configuration within E•G, with the nucleophilic 3'-OH making a nonproductive interaction with an active site metal ion termed MA and with the adjacent 2'-OH making no interaction. Upon S binding, a rearrangement occurs that allows both -OH groups to contact a different active site metal ion, termed M(C), to make what are likely to be their catalytic interactions. The reactive phosphoryl group on S promotes this change, presumably by repositioning the metal ions with respect to G. This conformational transition demonstrates local rearrangements within an otherwise folded RNA, underscoring RNA's difficulty in specifying a unique conformation and highlighting Nature's potential to use local transitions of RNA in complex function. © 2015 Sengupta et al.; Published by Cold Spring Harbor Laboratory Press for the RNA Society.

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.

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

PubMed

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

2013-08-14

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

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

NASA Astrophysics Data System (ADS)

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

2015-10-01

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

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.

Investigation into the morphology and structure of magnetic bentonite nanocomposites with their catalytic activity

NASA Astrophysics Data System (ADS)

Wan, Dong; Wang, Guanghua; Li, Wenbing; Wei, Xiaobi

2017-08-01

Al pillared bentonite-Fe3O4 nanocomposites (Fe3O4/Al-B) with controllable Fe3O4 particle sizes and loadings were synthesized by a simple in situ oxidation-precipitation method. The obtained samples were characterized by XRD, SEM, TEM, FTIR, XPS, VSM and N2 sorption. These results suggested that Fe3O4 was chemically anchored to the bentonite sheets via Fe-O-Si bonds, resulting in the formation of secondary pore structure. Three types of structure of Fe3O4/Al-B nanocomposites were proposed at different Fe3O4 loadings, varying from 40 to 80 wt%. The catalytic activity of the Fe3O4/Al-B nanocomposites was investigated in the heterogeneous Fenton-like oxidation of rhodamine B (RhB). The 50 nm Fe3O4/Al-B nanocomposite showed enhanced degradation of RhB over the control catalyst, benefited from its greater surface area and pore volume. The highest catalytic activity was found to be at Fe3O4 loading of 60 wt%, which was attributed to the synergistic effects between both increased surface area and formed Fe-O-Si bonds. These findings offer a better understanding on structural and morphological relationships of Fe3O4/Al-B nanocomposites with their heterogeneous Fenton-like catalytic activity.

Platinum nanoparticle during electrochemical hydrogen evolution: Adsorbate distribution, active reaction species, and size effect

DOE PAGES

Tan, Teck L.; Wang, Lin -Lin; Zhang, Jia; ...

2015-03-02

For small Pt nanoparticles (NPs), catalytic activity is, as observed, adversely affected by size in the 1–3 nm range. We elucidate, via first-principles-based thermodynamics, the operation H* distribution and cyclic voltammetry (CV) during the hydrogen evolution reaction (HER) across the electrochemical potential, including the underpotential region (U ≤ 0) that is difficult to assess in experiment. We consider multiple adsorption sites on a 1 nm Pt NP model and show that the characteristic CV peaks from different H* species correspond well to experiment. We next quantify the activity contribution from each H* species to explain the adverse effect of size.more » From the resolved CV peaks at the standard hydrogen electrode potential (U = 0), we first deduce that the active species for the HER are the partially covered (100)-facet bridge sites and the (111)-facet hollow sites. Upon evaluation of the reaction barriers at operation H* distribution and microkinetic modeling of the exchange current, we find that the nearest-neighbor (100)-facet bridge site pairs have the lowest activation energy and contribute to ~75% of the NP activity. Edge bridge sites (fully covered by H*) per se are not active; however, they react with neighboring (100)-facet H* to account for ~18% of the activity, whereas (111)-facet hollow sites contribute little. As a result, extrapolating the relative contributions to larger NPs in which the ratio of facet-to-edge sites increases, we show that the adverse size effect of Pt NP HER activity kicks in for sizes below 2 nm.« less

Twinning in fcc lattice creates low-coordinated catalytically active sites in porous gold

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

Krajčí, Marian; Kameoka, Satoshi; Tsai, An-Pang

We describe a new mechanism for creation of catalytically active sites in porous gold. Samples of porous gold prepared by de-alloying Al{sub 2}Au exhibit a clear correlation between the catalytic reactivity towards CO oxidation and structural defects in the fcc lattice of Au. We have found that on the stepped (211) surfaces quite common twin boundary defects in the bulk structure of porous gold can form long close-packed rows of atoms with the coordination number CN = 6. DFT calculations confirm that on these low-coordinated Au sites dioxygen chemisorbs and CO oxidation can proceed via the Langmuir–Hinshelwood mechanism with themore » activation energy of 37 kJ/mol or via the CO–OO intermediate with the energy barrier of 19 kJ/mol. The existence of the twins in porous gold is stabilized by the surface energy.« less

Catalytic Transfer Hydrogenation of Furfural to Furfuryl Alcohol over Nitrogen-Doped Carbon-Supported Iron Catalysts.

PubMed

Li, Jiang; Liu, Jun-Ling; Zhou, Hong-Jun; Fu, Yao

2016-06-08

Iron-based heterogeneous catalysts, which were generally prepared by pyrolysis of iron complexes on supports at elevated temperature, were found to be capable of catalyzing the transfer hydrogenation of furfural (FF) to furfuryl alcohol (FFA). The effects of metal precursor, nitrogen precursor, pyrolysis temperature, and support on catalytic performance were examined thoroughly, and a comprehensive study of the reaction parameters was also performed. The highest selectivity of FFA reached 83.0 % with a FF conversion of 91.6 % under the optimal reaction condition. Catalyst characterization suggested that iron cations coordinated by pyridinic nitrogen functionalities were responsible for the enhanced catalytic activity. The iron catalyst could be recycled without significant loss of catalytic activity for five runs, and the destruction of the nitrogen-iron species, the presence of crystallized Fe2 O3 phase, and the pore structure change were the main reasons for catalyst deactivation. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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.

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.

Methods and apparatuses for preparing a surface to have catalytic activity

DOEpatents

Cooks, Robert G [West Lafayette, IN; Peng, Wen-Ping [West Lafayette, IN; Ouyang, Zheng [West Lafayette, IN; Goodwin, Michael P [West Lafayette, IN

2011-03-22

The invention provides methods and apparatuses that utilize mass spectrometry for preparation of a surface to have catalytic activity through molecular soft-landing of mass selected ions. Mass spectrometry is used to generate combinations of atoms in a particular geometrical arrangement, and ion soft-landing selects this molecular entity or combination of entities and gently deposits the entity or combination intact onto a surface.

Additive Manufacturing of Catalytically Active Living Materials.

PubMed

Saha, Abhijit; Johnston, Trevor G; Shafranek, Ryan T; Goodman, Cassandra J; Zalatan, Jesse G; Storti, Duane W; Ganter, Mark A; Nelson, Alshakim

2018-04-25

Living materials, which are composites of living cells residing in a polymeric matrix, are designed to utilize the innate functionalities of the cells to address a broad range of applications such as fermentation and biosensing. Herein, we demonstrate the additive manufacturing of catalytically active living materials (AMCALM) for continuous fermentation. A multi-stimuli-responsive yeast-laden hydrogel ink, based on F127-dimethacrylate, was developed and printed using a direct-write 3D printer. The reversible stimuli-responsive behaviors of the polymer hydrogel inks to temperature and pressure are critical, as they enabled the facile incorporation of yeast cells and subsequent fabrication of 3D lattice constructs. Subsequent photo-cross-linking of the printed polymer hydrogel afforded a robust elastic material. These yeast-laden living materials were metabolically active in the fermentation of glucose into ethanol for 2 weeks in a continuous batch process without significant reduction in efficiency (∼90% yield of ethanol). This cell immobilization platform may potentially be applicable toward other genetically modified yeast strains to produce other high-value chemicals in a continuous biofermentation process.

Role of Coupled-Dynamics in the Catalytic Activity of Prokaryotic-like Prolyl-tRNA Synthetases

PubMed Central

Sanford, Brianne; Cao, Bach; Johnson, James M.; Zimmerman, Kurt; Strom, Alexander M.; Mueller, Robyn M.; Bhattacharyya, Sudeep; Musier-Forsyth, Karin; Hati, Sanchita

2012-01-01

Prolyl-tRNA synthetases (ProRSs) have been shown to activate both cognate and some noncognate amino acids and attach them to specific tRNAPro substrates. For example, alanine, which is smaller than cognate proline, is misactivated by Escherichia coli ProRS. Mischarged Ala-tRNAPro is hydrolyzed by an editing domain (INS) that is distinct from the activation domain. It was previously shown that deletion of the INS greatly reduced cognate proline activation efficiency. In the present study, experimental and computational approaches were used to test the hypothesis that INS deletion alters the internal protein dynamics leading to reduce catalytic function. Kinetic studies with two ProRS variants, G217A and E218A, revealed decreased amino acid activation efficiency. Molecular dynamics studies showed motional coupling between the INS and protein segments containing the catalytically important proline-binding loop (PBL, residues 199–206). In particular, the complete deletion of INS, as well as mutation of G217 or E218 to alanine, exhibited significant effects on the motion of the PBL. The presence of coupled-dynamics between neighboring protein segments was also observed through in silico mutations and essential dynamics analysis. Taken together, the present study demonstrates that structural elements at the editing domain-activation domain interface participate in coupled motions that facilitate amino acid binding and catalysis by bacterial ProRSs, which may explain why truncated or defunct editing domains have been maintained in some systems, despite the lack of catalytic activity. PMID:22356126

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

The C terminus of Ku80 activates the DNA-dependent protein kinase catalytic subunit.

PubMed

Singleton, B K; Torres-Arzayus, M I; Rottinghaus, S T; Taccioli, G E; Jeggo, P A

1999-05-01

Ku is a heterodimeric protein with double-stranded DNA end-binding activity that operates in the process of nonhomologous end joining. Ku is thought to target the DNA-dependent protein kinase (DNA-PK) complex to the DNA and, when DNA bound, can interact and activate the DNA-PK catalytic subunit (DNA-PKcs). We have carried out a 3' deletion analysis of Ku80, the larger subunit of Ku, and shown that the C-terminal 178 amino acid residues are dispensable for DNA end-binding activity but are required for efficient interaction of Ku with DNA-PKcs. Cells expressing Ku80 proteins that lack the terminal 178 residues have low DNA-PK activity, are radiation sensitive, and can recombine the signal junctions but not the coding junctions during V(D)J recombination. These cells have therefore acquired the phenotype of mouse SCID cells despite expressing DNA-PKcs protein, suggesting that an interaction between DNA-PKcs and Ku, involving the C-terminal region of Ku80, is required for DNA double-strand break rejoining and coding but not signal joint formation. To gain further insight into important domains in Ku80, we report a point mutational change in Ku80 in the defective xrs-2 cell line. This residue is conserved among species and lies outside of the previously reported Ku70-Ku80 interaction domain. The mutational change nonetheless abrogates the Ku70-Ku80 interaction and DNA end-binding activity.

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.

Engineered disulfide bonds increase active-site local stability and reduce catalytic activity of a cold-adapted alkaline phosphatase.

PubMed

Asgeirsson, Bjarni; Adalbjörnsson, Björn Vidar; Gylfason, Gudjón Andri

2007-06-01

Alkaline phosphatase is an extracellular enzyme that is membrane-bound in eukaryotes but resides in the periplasmic space of bacteria. It normally carries four cysteine residues that form two disulfide bonds, for instance in the APs of Escherichia coli and vertebrates. An AP variant from a Vibrio sp. has only one cysteine residue. This cysteine is second next to the nucleophilic serine in the active site. We have individually modified seven residues to cysteine that are on two loops predicted to be within a 5 A radius. Four of them formed a disulfide bond to the endogenous cysteine. Thermal stability was monitored by circular dichroism and activity measurements. Global stability was similar to the wild-type enzyme. However, a significant increase in heat-stability was observed for the disulfide-containing variants using activity as a measure, together with a large reduction in catalytic rates (k(cat)) and a general decrease in Km values. The results suggest that a high degree of mobility near the active site and in the helix carrying the endogenous cysteine is essential for full catalytic efficiency in the cold-adapted AP.

Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

NASA Astrophysics Data System (ADS)

Islam, A. E.; Nikolaev, P.; Amama, P. B.; Zakharov, D.; Sargent, G.; Saber, S.; Huffman, D.; Erford, M.; Semiatin, S. L.; Stach, E. A.; Maruyama, B.

2015-09-01

Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only in the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. With the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.

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

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

Volkov, Oleg A.; Kinch, Lisa; Ariagno, Carson

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

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

NASA Astrophysics Data System (ADS)

Zhan, Chang-Guo

2002-03-01

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

Anti-staphylococcal activities of lysostaphin and LytM catalytic domain

PubMed Central

2012-01-01

Background Lysostaphin and the catalytic domain of LytM cleave pentaglycine crossbridges of Staphylococcus aureus peptidoglycan. The bacteriocin lysostaphin is secreted by Staphylococcus simulans biovar staphylolyticus and directed against the cell walls of competing S. aureus. LytM is produced by S. aureus as a latent autolysin and can be activated in vitro by the removal of an N-terminal domain and occluding region. Results We compared the efficacies of the lysostaphin and LytM catalytic domains using a newly developed model of chronic S. aureus infected eczema. Lysostaphin was effective, like in other models. In contrast, LytM was not significantly better than control. The different treatment outcomes could be correlated with in vitro properties of the proteins, including proteolytic stability, affinity to cell wall components other than peptidoglycan, and sensitivity to the ionic milieu. Conclusions Although lysostaphin and LytM cleave the same peptide bond in the peptidoglycan, the two enzymes have very different environmental requirements what is reflected in their contrasting performance in mouse eczema model. PMID:22672475

The regulatory properties of rubisco activase differ among species and affect photosynthetic induction during light transitions

USDA-ARS?s Scientific Manuscript database

Rubisco’s catalytic chaperone, Rubisco activase (Rca), uses the energy from ATP hydrolysis to restore catalytic competence to Rubisco. In Arabidopsis, inhibition of Rca activity by ADP is fine-tuned by redox regulation of the a-isoform. To elucidate the mechanism for Rca regulation in species contai...

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.

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

Design of multi-shell Fe2O3@MnOx@CNTs for the selective catalytic reduction of NO with NH3: improvement of catalytic activity and SO2 tolerance

NASA Astrophysics Data System (ADS)

Cai, Sixiang; Hu, Hang; Li, Hongrui; Shi, Liyi; Zhang, Dengsong

2016-02-01

Manganese based catalysts are highly active in the NH3-SCR reaction for NOx removal. Unfortunately, manganese oxides can be easily deactivated by sulfur dioxide in the flow gas, which has become the main obstacle for their practical applications. To address this problem, we presented a green and facile method for the synthesis of multi-shell Fe2O3@MnOx@CNTs. The morphology and structural properties of the catalysts were systematically investigated. The results revealed that the MnOx@CNT core-shell structure was formed during the chemical bath deposition, while the outermost MnOx species were transformed to Fe2O3 after the galvanic replacement reaction. The formation of the multi-shell structure induced the enhancement of the active oxygen species, reducible species as well as adsorption of the reactants, which brought about excellent de-NOx performance. Moreover, the Fe2O3 shell could effectively suppress the formation of the surface sulfate species, leading to the desirable SO2 resistance to the multi-shell catalyst. Hence, the synthesis protocol could provide guidance for the preparation and elevation of manganese based catalysts.Manganese based catalysts are highly active in the NH3-SCR reaction for NOx removal. Unfortunately, manganese oxides can be easily deactivated by sulfur dioxide in the flow gas, which has become the main obstacle for their practical applications. To address this problem, we presented a green and facile method for the synthesis of multi-shell Fe2O3@MnOx@CNTs. The morphology and structural properties of the catalysts were systematically investigated. The results revealed that the MnOx@CNT core-shell structure was formed during the chemical bath deposition, while the outermost MnOx species were transformed to Fe2O3 after the galvanic replacement reaction. The formation of the multi-shell structure induced the enhancement of the active oxygen species, reducible species as well as adsorption of the reactants, which brought about excellent de

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

NASA Astrophysics Data System (ADS)

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

2016-10-01

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

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.

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.

Influence of hydrophobic mismatch on the catalytic activity of Escherichia coli GlpG rhomboid protease

PubMed Central

Foo, Alexander C Y; Harvey, Brandon G R; Metz, Jeff J; Goto, Natalie K

2015-01-01

Rhomboids comprise a broad family of intramembrane serine proteases that are found in a wide range of organisms and participate in a diverse array of biological processes. High-resolution structures of the catalytic transmembrane domain of the Escherichia coli GlpG rhomboid have provided numerous insights that help explain how hydrolytic cleavage can be achieved below the membrane surface. Key to this are observations that GlpG hydrophobic domain dimensions may not be sufficient to completely span the native lipid bilayer. This formed the basis for a model where hydrophobic mismatch Induces thinning of the local membrane environment to promote access to transmembrane substrates. However, hydrophobic mismatch also has the potential to alter the functional properties of the rhomboid, a possibility we explore in the current work. For this purpose, we purified the catalytic transmembrane domain of GlpG into phosphocholine or maltoside detergent micelles of varying alkyl chain lengths, and assessed proteolytic function with a model water-soluble substrate. Catalytic turnover numbers were found to depend on detergent alkyl chain length, with saturated chains containing 10–12 carbon atoms supporting maximal activity. Similar results were obtained in phospholipid bicelles, with no proteolytic activity being detected in longer-chain lipids. Although differences in thermal stability and GlpG oligomerization could not explain these activity differences, circular dichroism spectra suggest that mismatch gives rise to a small change in structure. Overall, these results demonstrate that hydrophobic mismatch can exert an inhibitory effect on rhomboid activity, with the potential for changes in local membrane environment to regulate activity in vivo. PMID:25307614

Long-range tertiary interactions in single hammerhead ribozymes bias motional sampling toward catalytically active conformations

PubMed Central

McDowell, S. Elizabeth; Jun, Jesse M.; Walter, Nils G.

2010-01-01

Enzymes generally are thought to derive their functional activity from conformational motions. The limited chemical variation in RNA suggests that such structural dynamics may play a particularly important role in RNA function. Minimal hammerhead ribozymes are known to cleave efficiently only in ∼10-fold higher than physiologic concentrations of Mg2+ ions. Extended versions containing native loop–loop interactions, however, show greatly enhanced catalytic activity at physiologically relevant Mg2+ concentrations, for reasons that are still ill-understood. Here, we use Mg2+ titrations, activity assays, ensemble, and single molecule fluorescence resonance energy transfer (FRET) approaches, combined with molecular dynamics (MD) simulations, to ask what influence the spatially distant tertiary loop–loop interactions of an extended hammerhead ribozyme have on its structural dynamics. By comparing hammerhead variants with wild-type, partially disrupted, and fully disrupted loop–loop interaction sequences we find that the tertiary interactions lead to a dynamic motional sampling that increasingly populates catalytically active conformations. At the global level the wild-type tertiary interactions lead to more frequent, if transient, encounters of the loop-carrying stems, whereas at the local level they lead to an enrichment in favorable in-line attack angles at the cleavage site. These results invoke a linkage between RNA structural dynamics and function and suggest that loop–loop interactions in extended hammerhead ribozymes—and Mg2+ ions that bind to minimal ribozymes—may generally allow more frequent access to a catalytically relevant conformation(s), rather than simply locking the ribozyme into a single active state. PMID:20921269

Cobalt-doping-induced synthesis of ceria nanodisks and their significantly enhanced catalytic activity.

PubMed

Guo, Xiao-Hui; Mao, Chao-Chao; Zhang, Ji; Huang, Jun; Wang, Wa-Nv; Deng, Yong-Hui; Wang, Yao-Yu; Cao, Yong; Huang, Wei-Xin; Yu, Shu-Hong

2012-05-21

High-quality cobalt-doped ceria nanostructures with triangular column, triangular slab, and disklike shapes are synthesized by tuning the doping amount of cobalt nitrate in a facile hydrothermal reaction. The cobalt-doped ceria nanodisks display significantly enhanced catalytic activity in CO oxidation due to exposed highly active crystal planes and the presence of numerous surface defects. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies Relevent to Catalytic Activation Co & other small Molecules

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

Ford, Peter C

2005-02-22

Detailed annual and triannual reports describing the progress accomplished during the tenure of this grant were filed with the Program Manager for Catalysis at the Office of Basic Energy Sciences. To avoid unnecessary duplication, the present report will provide a brief overview of the research areas that were sponsored by this grant and list the resulting publications and theses based on this DOE supported research. The scientific personnel participating in (and trained by) this grant's research are also listed. Research carried out under this DOE grant was largely concerned with the mechanisms of the homogeneous catalytic and photocatalytic activation ofmore » small molecules such as carbon monoxide, dihydrogen and various hydrocarbons. Much of the more recent effort has focused on the dynamics and mechanisms of reactions relevant to substrate carbonylations by homogeneous organometallic catalysts. A wide range of modern investigative techniques were employed, including quantitative fast reaction methodologies such as time-resolved optical (TRO) and time-resolved infrared (TRIR) spectroscopy and stopped flow kinetics. Although somewhat diverse, this research falls within the scope of the long-term objective of applying quantitative techniques to elucidate the dynamics and understand the principles of mechanisms relevant to the selective and efficient catalytic conversions of fundamental feedstocks to higher value materials.« less

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

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.

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.

Radiation/Catalytic Augmented Combustion.

DTIC Science & Technology

1984-05-01

interest to compare the experimental results for the solid bluff body with a thuoretical result. Using simple argtinieiiLs from fluid mechanics " one...responsibility through completion. Dr. A. E. Cerkanowlcz assisted in writing this final report. Experimental studies on catalytic augmented combustion...as well as with other combustion species, lead to ignition and sustained combustion via chain reactions. Simple combustion enhancement without

The catalytic cycle of nitrous oxide reductase - The enzyme that catalyzes the last step of denitrification.

PubMed

Carreira, Cíntia; Pauleta, Sofia R; Moura, Isabel

2017-12-01

The reduction of the potent greenhouse gas nitrous oxide requires a catalyst to overcome the large activation energy barrier of this reaction. Its biological decomposition to the inert dinitrogen can be accomplished by denitrifiers through nitrous oxide reductase, the enzyme that catalyzes the last step of the denitrification, a pathway of the biogeochemical nitrogen cycle. Nitrous oxide reductase is a multicopper enzyme containing a mixed valence CuA center that can accept electrons from small electron shuttle proteins, triggering electron flow to the catalytic sulfide-bridged tetranuclear copper "CuZ center". This enzyme has been isolated with its catalytic center in two forms, CuZ*(4Cu1S) and CuZ(4Cu2S), proven to be spectroscopic and structurally different. In the last decades, it has been a challenge to characterize the properties of this complex enzyme, due to the different oxidation states observed for each of its centers and the heterogeneity of its preparations. The substrate binding site in those two "CuZ center" forms and which is the active form of the enzyme is still a matter of debate. However, in the last years the application of different spectroscopies, together with theoretical calculations have been useful in answering these questions and in identifying intermediate species of the catalytic cycle. An overview of the spectroscopic, kinetics and structural properties of the two forms of the catalytic "CuZ center" is given here, together with the current knowledge on nitrous oxide reduction mechanism by nitrous oxide reductase and its intermediate species. Copyright © 2017 Elsevier Inc. All rights reserved.

Catalytic therapy of cancer by ascorbic acid involves redox cycling of exogenous/endogenous copper ions and generation of reactive oxygen species.

PubMed

Hadi, S M; Ullah, M F; Shamim, U; Bhatt, S H; Azmi, A S

2010-01-01

Catalytic therapy is a cancer treatment modality based on the generation of reactive oxygen species (ROS) through administration of ascorbate/medicinal herbal extracts and copper. It is known that antioxidants such as ascorbate also exhibit prooxidant activity in the presence of transition metals such as copper. Based on our work and that in the literature, in this review we propose a mechanism for the cytotoxic action of ascorbate against cancer cells. It involves redox cycling of exogenous/endogenous copper ions and the consequent generation of ROS leading to oxidative DNA breakage. Using human peripheral lymphocytes and the Comet assay, we have shown that ascorbic acid is able to cause oxidative breakage in cellular DNA. Such DNA degradation is inhibited by neocuproine (a Cu(I) sequestering agent) and scavengers of ROS indicating that the cellular DNA breakage involves the generation of Cu(I) and formation of ROS. Similar results are also obtained with plant polyphenol antioxidants that are important constituents of medicinal herbal extracts. Copper is an essential component of chromatin and can take part in redox reactions. It is well established that tissue, cellular and serum copper levels are considerably elevated in various malignancies. Therefore, cancer cells may be more subject to electron transfer between copper ions and ascorbate/plant polyphenols to generate ROS. In this review we cite evidence to indicate that in catalytic therapy cytotoxic action against cancer cells involves redox cycling of exogenous/endogenous copper ions. Copyright © 2010 S. Karger AG, Basel.

Dynamic Modification of Pore Opening of SAPO-34 by Adsorbed Surface Methoxy Species during Induction of Catalytic Methanol-to-Olefins Reactions

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

Lo, Benedict T W.; Ye, Lin; Change, G.G. Z.

Here, we report that the pore opening of SAPO-34 can be significantly modified by an adsorbed surface methoxy species during induction of the catalytic methanol-to-olefins process, which offers molecular sieving properties due to physical obstacle of the methoxy group and its adsorption modification to other hydrocarbons. X-ray powder diffraction and Rietveld refinement clearly reveal that the adsorbed single carbon atom as the methoxy group is dynamically created from methanol dehydration on a Brønsted acid site in close proximity to the pore windows. As a result, industrial desirable smaller olefins such as ethylene and propylene can be favourably made at themore » expenses of higher olefins. The structures and fundamental understanding in alteration in the olefins selectivity during induction may allow rational optimisation in catalytic performance under the complex fluidisation conditions.« less

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

NASA Astrophysics Data System (ADS)

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

2015-04-01

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

A microreactor array for spatially resolved measurement of catalytic activity for high-throughput catalysis science

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

Kondratyuk, Petro; Gumuslu, Gamze; Shukla, Shantanu

2013-04-01

We describe a 100 channel microreactor array capable of spatially resolved measurement of catalytic activity across the surface of a flat substrate. When used in conjunction with a composition spread alloy film (CSAF, e.g. Pd{sub x}Cu{sub y}Au{sub 1-x-y}) across which component concentrations vary smoothly, such measurements permit high-throughput analysis of catalytic activity and selectivity as a function of catalyst composition. In the reported implementation, the system achieves spatial resolution of 1 mm{sup 2} over a 10×10 mm{sup 2} area. During operation, the reactant gases are delivered at constant flow rate to 100 points of differing composition on the CSAF surfacemore » by means of a 100-channel microfluidic device. After coming into contact with the CSAF catalyst surface, the product gas mixture from each of the 100 points is withdrawn separately through a set of 100 isolated channels for analysis using a mass spectrometer. We demonstrate the operation of the device on a Pd{sub x}Cu{sub y}Au{sub 1-x-y} CSAF catalyzing the H{sub 2}-D{sub 2} exchange reaction at 333 K. In essentially a single experiment, we measured the catalytic activity over a broad swathe of concentrations from the ternary composition space of the Pd{sub x}Cu{sub y}Au{sub 1-x-y} alloy.« less

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

PubMed

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

2016-06-01

TRIM E3 ubiquitin ligases regulate a wide variety of cellular processes and are particularly important during innate immune signalling events. They are characterized by a conserved tripartite motif in their N-terminal portion which comprises a canonical RING domain, one or two B-box domains and a coiled-coil region that mediates ligase dimerization. Self-association via the coiled-coil has been suggested to be crucial for catalytic activity of TRIMs; however, the precise molecular mechanism underlying this observation remains elusive. Here, we provide a detailed characterization of the TRIM ligases TRIM25 and TRIM32 and show how their oligomeric state is linked to catalytic activity. The crystal structure of a complex between the TRIM25 RING domain and an ubiquitin-loaded E2 identifies the structural and mechanistic features that promote a closed E2~Ub conformation to activate the thioester for ubiquitin transfer allowing us to propose a model for the regulation of activity in the full-length protein. Our data reveal an unexpected diversity in the self-association mechanism of TRIMs that might be crucial for their biological function. © 2016 Francis Crick Institute. Published under the terms of the CC BY 4.0 license.

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

PubMed

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

2015-10-14

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

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.

Engineering catalytic activity via ion beam bombardment of catalyst supports for vertically aligned carbon nanotube growth

DOE PAGES

Islam, A. E.; Zakharov, D.; Stach, E. A.; ...

2015-09-16

Carbon nanotube growth depends on the catalytic activity of metal nanoparticles on alumina or silica supports. The control on catalytic activity is generally achieved by variations in water concentration, carbon feed, and sample placement on a few types of alumina or silica catalyst supports obtained via thin film deposition. We have recently expanded the choice of catalyst supports by engineering inactive substrates like c-cut sapphire via ion beam bombardment. The deterministic control on the structure and chemistry of catalyst supports obtained by tuning the degree of beam-induced damage have enabled better regulation of the activity of Fe catalysts only inmore » the ion beam bombarded areas and hence enabled controllable super growth of carbon nanotubes. A wide range of surface characterization techniques were used to monitor the catalytically active surface engineered via ion beam bombardment. The proposed method offers a versatile way to control carbon nanotube growth in patterned areas and also enhances the current understanding of the growth process. As a result, with the right choice of water concentration, carbon feed and sample placement, engineered catalyst supports may extend the carbon nanotube growth yield to a level that is even higher than the ones reported here, and thus offers promising applications of carbon nanotubes in electronics, heat exchanger, and energy storage.« less

Pt skin coated hollow Ag-Pt bimetallic nanoparticles with high catalytic activity for oxygen reduction reaction

NASA Astrophysics Data System (ADS)

Fu, Tao; Huang, Jianxing; Lai, Shaobo; Zhang, Size; Fang, Jun; Zhao, Jinbao

2017-10-01

The catalytic activity and stability of electrocatalyst is critical for the commercialization of fuel cells, and recent reports reveal the great potential of the hollow structures with Pt skin coat for developing high-powered electrocatalysts due to their highly efficient utilization of the Pt atoms. Here, we provide a novel strategy to prepare the Pt skin coated hollow Ag-Pt structure (Ag-Pt@Pt) of ∼8 nm size at room temperature. As loaded on the graphene, the Ag-Pt@Pt exhibits a remarkable mass activity of 0.864 A/mgPt (at 0.9 V, vs. reversible hydrogen electrode (RHE)) towards oxygen reduction reaction (ORR), which is 5.30 times of the commercial Pt/C catalyst, and the Ag-Pt@Pt also shows a better stability during the ORR catalytic process. The mechanism of this significant enhancement can be attributed to the higher Pt utilization and the unique Pt on Ag-Pt surface structure, which is confirmed by the density functional theory (DFT) calculations and other characterization methods. In conclusion, this original work offers a low-cost and environment-friendly method to prepare a high active electrocatalyst with cheaper price, and this work also discloses the correlation between surface structures and ORR catalytic activity for the hollow structures with Pt skin coat, which can be instructive for designing novel advanced electrocatalysts for fuel cells.

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.

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.

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

NASA Technical Reports Server (NTRS)

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

1998-01-01

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

Structural Basis for Catalytic Activation of a Serine Recombinase

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

Keenholtz, Ross A.; Rowland, Sally-J.; Boocock, Martin R.

2014-10-02

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

Multifaceted catalytic hydrogenation of amides via diverse activation of a sterically confined bipyridine-ruthenium framework.

PubMed

Miura, Takashi; Naruto, Masayuki; Toda, Katsuaki; Shimomura, Taiki; Saito, Susumu

2017-05-16

Amides are ubiquitous and abundant in nature and our society, but are very stable and reluctant to salt-free, catalytic chemical transformations. Through the activation of a "sterically confined bipyridine-ruthenium (Ru) framework (molecularly well-designed site to confine adsorbed H 2 in)" of a precatalyst, catalytic hydrogenation of formamides through polyamide is achieved under a wide range of reaction conditions. Both C=O bond and C-N bond cleavage of a lactam became also possible using a single precatalyst. That is, catalyst diversity is induced by activation and stepwise multiple hydrogenation of a single precatalyst when the conditions are varied. The versatile catalysts have different structures and different resting states for multifaceted amide hydrogenation, but the common structure produced upon reaction with H 2 , which catalyzes hydrogenation, seems to be "H-Ru-N-H."

Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting

PubMed Central

Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

2015-01-01

Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated. PMID:25749635

Photo-catalytic Activities of Plant Hormones on Semiconductor Nanoparticles by Laser-Activated Electron Tunneling and Emitting

NASA Astrophysics Data System (ADS)

Tang, Xuemei; Huang, Lulu; Zhang, Wenyang; Jiang, Ruowei; Zhong, Hongying

2015-03-01

Understanding of the dynamic process of laser-induced ultrafast electron tunneling is still very limited. It has been thought that the photo-catalytic reaction of adsorbents on the surface is either dependent on the number of resultant electron-hole pairs where excess energy is lost to the lattice through coupling with phonon modes, or dependent on irradiation photon wavelength. We used UV (355 nm) laser pulses to excite electrons from the valence band to the conduction band of titanium dioxide (TiO2), zinc oxide (ZnO) and bismuth cobalt zinc oxide (Bi2O3)0.07(CoO)0.03(ZnO)0.9 semiconductor nanoparticles with different photo catalytic properties. Photoelectrons are extracted, accelerated in a static electric field and eventually captured by charge deficient atoms of adsorbed organic molecules. A time-of-flight mass spectrometer was used to detect negative molecules and fragment ions generated by un-paired electron directed bond cleavages. We show that the probability of electron tunneling is determined by the strength of the static electric field and intrinsic electron mobility of semiconductors. Photo-catalytic dissociation or polymerization reactions of adsorbents are highly dependent on the kinetic energy of tunneling electrons as well as the strength of laser influx. By using this approach, photo-activities of phytohormones have been investigated.

Process for forming a homogeneous oxide solid phase of catalytically active material

DOEpatents

Perry, Dale L.; Russo, Richard E.; Mao, Xianglei

1995-01-01

A process is disclosed for forming a homogeneous oxide solid phase reaction product of catalytically active material comprising one or more alkali metals, one or more alkaline earth metals, and one or more Group VIII transition metals. The process comprises reacting together one or more alkali metal oxides and/or salts, one or more alkaline earth metal oxides and/or salts, one or more Group VIII transition metal oxides and/or salts, capable of forming a catalytically active reaction product, in the optional presence of an additional source of oxygen, using a laser beam to ablate from a target such metal compound reactants in the form of a vapor in a deposition chamber, resulting in the deposition, on a heated substrate in the chamber, of the desired oxide phase reaction product. The resulting product may be formed in variable, but reproducible, stoichiometric ratios. The homogeneous oxide solid phase product is useful as a catalyst, and can be produced in many physical forms, including thin films, particulate forms, coatings on catalyst support structures, and coatings on structures used in reaction apparatus in which the reaction product of the invention will serve as a catalyst.

Influence of dopant substitution mechanism on catalytic properties within hierarchical architectures

NASA Astrophysics Data System (ADS)

Newland, Stephanie H.; Sinkler, Wharton; Mezza, Thomas; Bare, Simon R.; Raja, Robert

2016-07-01

A range of hierarchically porous (HP) AlPO-5 catalysts, with isomorphously substituted transition metal ions, have been synthesized using an organosilane as a soft template. By employing a range of structural and spectroscopic characterization protocols, the properties of the dopant-substituted species within the HP architectures have been carefully evaluated. The resulting nature of the active site is shown to have a direct impact on the ensuing catalytic properties in the liquid-phase Beckmann rearrangement of cyclic ketones.

Dynamics of the active site architecture in plant-type ferredoxin-NADP(+) reductases catalytic complexes.

PubMed

Sánchez-Azqueta, Ana; Catalano-Dupuy, Daniela L; López-Rivero, Arleth; Tondo, María Laura; Orellano, Elena G; Ceccarelli, Eduardo A; Medina, Milagros

2014-10-01

Kinetic isotope effects in reactions involving hydride transfer and their temperature dependence are powerful tools to explore dynamics of enzyme catalytic sites. In plant-type ferredoxin-NADP(+) reductases the FAD cofactor exchanges a hydride with the NADP(H) coenzyme. Rates for these processes are considerably faster for the plastidic members (FNR) of the family than for those belonging to the bacterial class (FPR). Hydride transfer (HT) and deuteride transfer (DT) rates for the NADP(+) coenzyme reduction of four plant-type FNRs (two representatives of the plastidic type FNRs and the other two from the bacterial class), and their temperature dependences are here examined applying a full tunnelling model with coupled environmental fluctuations. Parameters for the two plastidic FNRs confirm a tunnelling reaction with active dynamics contributions, but isotope effects on Arrhenius factors indicate a larger contribution for donor-acceptor distance (DAD) dynamics in the Pisum sativum FNR reaction than in the Anabaena FNR reaction. On the other hand, parameters for bacterial FPRs are consistent with passive environmental reorganisation movements dominating the HT coordinate and no contribution of DAD sampling or gating fluctuations. This indicates that active sites of FPRs are more organised and rigid than those of FNRs. These differences must be due to adaptation of the active sites and catalytic mechanisms to fulfil their particular metabolic roles, establishing a compromise between protein flexibility and functional optimisation. Analysis of site-directed mutants in plastidic enzymes additionally indicates the requirement of a minimal optimal architecture in the catalytic complex to provide a favourable gating contribution. Copyright © 2014 Elsevier B.V. All rights reserved.

Accumulating the hydride state in the catalytic cycle of [FeFe]-hydrogenases

NASA Astrophysics Data System (ADS)

Winkler, Martin; Senger, Moritz; Duan, Jifu; Esselborn, Julian; Wittkamp, Florian; Hofmann, Eckhard; Apfel, Ulf-Peter; Stripp, Sven Timo; Happe, Thomas

2017-07-01

H2 turnover at the [FeFe]-hydrogenase cofactor (H-cluster) is assumed to follow a reversible heterolytic mechanism, first yielding a proton and a hydrido-species which again is double-oxidized to release another proton. Three of the four presumed catalytic intermediates (Hox, Hred/Hred and Hsred) were characterized, using various spectroscopic techniques. However, in catalytically active enzyme, the state containing the hydrido-species, which is eponymous for the proposed heterolytic mechanism, has yet only been speculated about. We use different strategies to trap and spectroscopically characterize this transient hydride state (Hhyd) for three wild-type [FeFe]-hydrogenases. Applying a novel set-up for real-time attenuated total-reflection Fourier-transform infrared spectroscopy, we monitor compositional changes in the state-specific infrared signatures of [FeFe]-hydrogenases, varying buffer pH and gas composition. We selectively enrich the equilibrium concentration of Hhyd, applying Le Chatelier's principle by simultaneously increasing substrate and product concentrations (H2/H+). Site-directed manipulation, targeting either the proton-transfer pathway or the adt ligand, significantly enhances Hhyd accumulation independent of pH.

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%.

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

PubMed

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

2017-01-01

Designing catalysts that achieve the rates and selectivities of natural enzymes is a long-standing goal in protein chemistry. Here, we show that an ultrahigh-throughput droplet-based microfluidic screening platform can be used to improve a previously optimized artificial aldolase by an additional factor of 30 to give a >10 9 rate enhancement that rivals the efficiency of class I aldolases. The resulting enzyme catalyses a reversible aldol reaction with high stereoselectivity and tolerates a broad range of substrates. Biochemical and structural studies show that catalysis depends on a Lys-Tyr-Asn-Tyr tetrad that emerged adjacent to a computationally designed hydrophobic pocket during directed evolution. This constellation of residues is poised to activate the substrate by Schiff base formation, promote mechanistically important proton transfers and stabilize multiple transition states along a complex reaction coordinate. The emergence of such a sophisticated catalytic centre shows that there is nothing magical about the catalytic activities or mechanisms of naturally occurring enzymes, or the evolutionary process that gave rise to them.

Hot-electron-mediated surface chemistry: toward electronic control of catalytic activity.

PubMed

Park, Jeong Young; Kim, Sun Mi; Lee, Hyosun; Nedrygailov, Ievgen I

2015-08-18

nanoparticles on oxide supports and Pt-CdSe-Pt nanodumbbells. We show that the accumulation or depletion of hot electrons on metal nanoparticles, in turn, can also influence catalytic reactions. Mechanisms suggested for hot-electron-induced chemical reactions on a photoexcited plasmonic metal are discussed. We propose that the manipulation of the flow of hot electrons by changing the electrical characteristics of metal-oxide and metal-semiconductor interfaces can give rise to the intriguing capability of tuning the catalytic activity of hybrid nanocatalysts.

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.

Influence of dopant substitution mechanism on catalytic properties within hierarchical architectures

PubMed Central

Newland, Stephanie H.; Sinkler, Wharton; Mezza, Thomas; Bare, Simon R.

2016-01-01

A range of hierarchically porous (HP) AlPO-5 catalysts, with isomorphously substituted transition metal ions, have been synthesized using an organosilane as a soft template. By employing a range of structural and spectroscopic characterization protocols, the properties of the dopant-substituted species within the HP architectures have been carefully evaluated. The resulting nature of the active site is shown to have a direct impact on the ensuing catalytic properties in the liquid-phase Beckmann rearrangement of cyclic ketones. PMID:27493563

W-incorporated CoMo/{lambda}-Al{sub 2}O{sub 3} hydrodesulfurization catalyst. I. Catalytic activities

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

Lee, D.K.; Lee, I.C.; Park, S.K.

1996-03-01

The promotional effect of tungsten in the CoMo/{gamma}-Al{sub 2}O{sub 3} catalyst was studied for series of W-incorporated CoMo/{gamma}-Al{sub 2}O{sub 3} catalysts with different content of tungsten. Two series of the catalysts were prepared by changing the impregnation order of cobalt and tungsten onto a base Mo/{gamma}-Al{sub 2}O{sub 3} catalyst. Impregnation of tungsten was achieved under the condition that the pH of an aqueous impregnating solution of W anion was controlled to 9.5. The hydrodesulfurization (HDS) and hydrogenation (HYD) activities of the sulfided catalysts were evaluated by thiophene HDS and ethylene HYD reactions at atmospheric pressure, respectively. Low-temperature O{sub 2} chemisorptionmore » at 195 K was conducted for the sulfided catalysts in order to determine the W-incorporation effects on the surface concentration of coordinatively unsaturated sites related to the catalytic activities. The dependence of catalytic activities on tungsten content showed initially an increase and subsequent decrease with increasing tungsten content. The maximum promotion of HDS and HYD activities occurred at a low content of tungsten corresponding to 0.025 in W/(W + Mo) atomic ratio regardless of the impregnation order of tungsten and cobalt. Oxygen uptake correlated well with catalytic activities. In general, the catalysts prepared by impregnating tungsten onto the CoMo/{gamma}-Al{sub 2}O{sub 3} showed higher activities than the catalysts prepared by impregnating tungsten onto Mo/{gamma}-Al{sub 2}O{sub 3} prior to impregnation of cobalt. 37 refs., 7 figs., 2 tabs.« less

Preparation and catalytic activities for H{sub 2}O{sub 2} decomposition of Rh/Au bimetallic nanoparticles

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

Zhang, Haijun, E-mail: zhanghaijun@wust.edu.cn; The State Key Laboratory of Refractory and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081; Deng, Xiangong

2016-07-15

Graphical abstract: PVP-protected Rh/Au bimetallic nanoparticles (BNPs) were prepared by using hydrogen sacrificial reduction method, the activity of Rh80Au20 BNPs were about 3.6 times higher than that of Rh NPs. - Highlights: • Rh/Au bimetallic nanoparticles (BNPs) of 3∼5 nm in diameter were prepared. • Activity for H{sub 2}O{sub 2} decomposition of BNPs is 3.6 times higher than that of Rh NPs. • The high activity of BNPs was caused by the existence of charged Rh atoms. • The apparent activation energy for H{sub 2}O{sub 2} decomposition over the BNPs was calculated. - Abstract: PVP-protected Rh/Au bimetallic nanoparticles (BNPs) weremore » prepared by using hydrogen sacrificial reduction method and characterized by UV–vis, XRD, FT-IR, XPS, TEM, HR-TEM and DF-STEM, the effects of composition on their particle sizes and catalytic activities for H{sub 2}O{sub 2} decomposition were also studied. The as-prepared Rh/Au BNPs possessed a high catalytic activity for the H{sub 2}O{sub 2} decomposition, and the activity of the Rh{sub 80}Au{sub 20} BNPs with average size of 2.7 nm were about 3.6 times higher than that of Rh monometallic nanoparticles (MNPs) even the Rh MNPs possess a smaller particle size of 1.7 nm. In contrast, Au MNPs with size of 2.7 nm show no any activity. Density functional theory (DFT) calculation as well as XPS results showed that charged Rh and Au atoms formed via electronic charge transfer effects could be responsible for the high catalytic activity of the BNPs.« less

Nanorods, nanospheres, nanocubes: Synthesis, characterization and catalytic activity of nanoferrites of Mn, Co, Ni, Part-89

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

Singh, Supriya; Srivastava, Pratibha; Singh, Gurdip, E-mail: gsingh4us@yahoo.com

2013-02-15

Graphical abstract: Prepared nanoferrites were characterized by FE-SEM and bright field TEM micrographs. The catalytic effect of these nanoferrites was evaluated on the thermal decomposition of ammonium perchlorate using TG and TG–DSC techniques. The kinetics of thermal decomposition of AP was evaluated using isothermal TG data by model fitting as well as isoconversional method. Display Omitted Highlights: ► Synthesis of ferrite nanostructures (∼20.0 nm) by wet-chemical method under different synthetic conditions. ► Characterization using XRD, FE-SEM, EDS, TEM, HRTEM and SAED pattern. ► Catalytic activity of ferrite nanostructures on AP thermal decomposition by thermal techniques. ► Burning rate measurements ofmore » CSPs with ferrite nanostructures. ► Kinetics of thermal decomposition of AP + nanoferrites. -- Abstract: In this paper, the nanoferrites of Mn, Co and Ni were synthesized by wet chemical method and characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive, X-ray spectra (EDS), transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HR-TEM). It is catalytic activity were investigated on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellants (CSPs) using thermogravimetry (TG), TG coupled with differential scanning calorimetry (TG–DSC) and ignition delay measurements. Kinetics of thermal decomposition of AP + nanoferrites have also been investigated using isoconversional and model fitting approaches which have been applied to data for isothermal TG decomposition. The burning rate of CSPs was considerably enhanced by these nanoferrites. Addition of nanoferrites to AP led to shifting of the high temperature decomposition peak toward lower temperature. All these studies reveal that ferrite nanorods show the best catalytic activity superior to that of nanospheres and nanocubes.« less

Probing the electrostatics of active site microenvironments along the catalytic cycle for Escherichia coli dihydrofolate reductase.

PubMed

Liu, C Tony; Layfield, Joshua P; Stewart, Robert J; French, Jarrod B; Hanoian, Philip; Asbury, John B; Hammes-Schiffer, Sharon; Benkovic, Stephen J

2014-07-23

Electrostatic interactions play an important role in enzyme catalysis by guiding ligand binding and facilitating chemical reactions. These electrostatic interactions are modulated by conformational changes occurring over the catalytic cycle. Herein, the changes in active site electrostatic microenvironments are examined for all enzyme complexes along the catalytic cycle of Escherichia coli dihydrofolate reductase (ecDHFR) by incorporation of thiocyanate probes at two site-specific locations in the active site. The electrostatics and degree of hydration of the microenvironments surrounding the probes are investigated with spectroscopic techniques and mixed quantum mechanical/molecular mechanical (QM/MM) calculations. Changes in the electrostatic microenvironments along the catalytic environment lead to different nitrile (CN) vibrational stretching frequencies and (13)C NMR chemical shifts. These environmental changes arise from protein conformational rearrangements during catalysis. The QM/MM calculations reproduce the experimentally measured vibrational frequency shifts of the thiocyanate probes across the catalyzed hydride transfer step, which spans the closed and occluded conformations of the enzyme. Analysis of the molecular dynamics trajectories provides insight into the conformational changes occurring between these two states and the resulting changes in classical electrostatics and specific hydrogen-bonding interactions. The electric fields along the CN axes of the probes are decomposed into contributions from specific residues, ligands, and solvent molecules that make up the microenvironments around the probes. Moreover, calculation of the electric field along the hydride donor-acceptor axis, along with decomposition of this field into specific contributions, indicates that the cofactor and substrate, as well as the enzyme, impose a substantial electric field that facilitates hydride transfer. Overall, experimental and theoretical data provide evidence for

Probing the Electrostatics of Active Site Microenvironments along the Catalytic Cycle for Escherichia coli Dihydrofolate Reductase

PubMed Central

2015-01-01

Electrostatic interactions play an important role in enzyme catalysis by guiding ligand binding and facilitating chemical reactions. These electrostatic interactions are modulated by conformational changes occurring over the catalytic cycle. Herein, the changes in active site electrostatic microenvironments are examined for all enzyme complexes along the catalytic cycle of Escherichia coli dihydrofolate reductase (ecDHFR) by incorporation of thiocyanate probes at two site-specific locations in the active site. The electrostatics and degree of hydration of the microenvironments surrounding the probes are investigated with spectroscopic techniques and mixed quantum mechanical/molecular mechanical (QM/MM) calculations. Changes in the electrostatic microenvironments along the catalytic environment lead to different nitrile (CN) vibrational stretching frequencies and 13C NMR chemical shifts. These environmental changes arise from protein conformational rearrangements during catalysis. The QM/MM calculations reproduce the experimentally measured vibrational frequency shifts of the thiocyanate probes across the catalyzed hydride transfer step, which spans the closed and occluded conformations of the enzyme. Analysis of the molecular dynamics trajectories provides insight into the conformational changes occurring between these two states and the resulting changes in classical electrostatics and specific hydrogen-bonding interactions. The electric fields along the CN axes of the probes are decomposed into contributions from specific residues, ligands, and solvent molecules that make up the microenvironments around the probes. Moreover, calculation of the electric field along the hydride donor–acceptor axis, along with decomposition of this field into specific contributions, indicates that the cofactor and substrate, as well as the enzyme, impose a substantial electric field that facilitates hydride transfer. Overall, experimental and theoretical data provide evidence for

The catalytic activity of a recombinant single chain variable fragment nucleic acid-hydrolysing antibody varies with fusion tag and expression host.

PubMed

Lee, Joungmin; Kim, Minjae; Seo, Youngsil; Lee, Yeonjin; Park, Hyunjoon; Byun, Sung June; Kwon, Myung-Hee

2017-11-01

The antigen-binding properties of single chain Fv antibodies (scFvs) can vary depending on the position and type of fusion tag used, as well as the host cells used for expression. The issue is even more complicated with a catalytic scFv antibody that binds and hydrolyses a specific antigen. Herein, we investigated the antigen-binding and -hydrolysing activities of the catalytic anti-nucleic acid antibody 3D8 scFv expressed in Escherichia coli or HEK293f cells with or without additional amino acid residues at the N- and C-termini. DNA-binding activity was retained in all recombinant forms. However, the DNA-hydrolysing activity varied drastically between forms. The DNA-hydrolysing activity of E. coli-derived 3D8 scFvs was not affected by the presence of a C-terminal human influenza haemagglutinin (HA) or His tag. By contrast, the activity of HEK293f-derived 3D8 scFvs was completely lost when additional residues were included at the N-terminus and/or when a His tag was incorporated at the C-terminus, whereas a HA tag at the C-terminus did not diminish activity. Thus, we demonstrate that the antigen-binding and catalytic activities of a catalytic antibody can be separately affected by the presence of additional residues at the N- and C-termini, and by the host cell type. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.

Effects of Detergents on Catalytic Activity of Human Endometase/Matrilysin-2, a Putative Cancer Biomarker†

PubMed Central

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

2009-01-01

Matrix metalloproteinases (MMPs) are a family of hydrolytic enzymes that play significant roles in development, morphogenesis, inflammation, and cancer invasion. Endometase (matrilysin 2 or MMP-26) is a putative early biomarker for human carcinomas. The effects of the ionic and nonionic detergents on catalytic activity of endometase were investigated. The hydrolytic activity of endometase was detergent concentration-dependent exhibiting a bell-shaped curve with its maximum activity near the critical micelle concentration (CMC) of nonionic detergents tested. The effect of Brij-35 on human gelatinase B (MMP-9), matirilysin (MMP-7), and membrane-type 1 MMP (MT1-MMP) was further explored. Their maximum catalysis was observed near the CMC of Brij-35 (~90 μM). Their IC50 values were above the CMC. The inhibition mechanism of MMP-7, MMP-9, and MT1-MMP by Brij-35 was mixed-type as determined by Dixon’s plot, however, that of endometase was non-competitive with a Ki value of 240 μM. The catalytic activities of MMPs are influenced by detergents. Monomer of detergents may activate and stabilize MMPs to enhance catalysis, but micelle of detergents may sequester enzyme and block substrate binding site to impede catalysis. Under physiological conditions lipid or membrane microenvironment may regulate enzymatic activity. PMID:19818727

Catalytic, hollow, refractory spheres

NASA Technical Reports Server (NTRS)

Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)

1987-01-01

Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

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

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.

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.

Transient species involved in catalytic dioxygen/peroxide activation by hemoproteins: possible involvement of protonated Compound I species.

PubMed

Silaghi-Dumitrescu, Radu; Cooper, Chris E

2005-11-07

Interaction of hemoproteins with peroxide leads in several cases to transient formation of ferric peroxo, ferric hydroperoxo, and "high-valent", formally Fev, oxo or hydroxo Compound species. Here, density functional calculations on ferric peroxo, ferric hydroperoxo, Compound and protonated Compound heme active site models are reported. The theoretical results, including calculated isotropic Fermi contact couplings and anisotropic spin dipole couplings, are found to generally correlate well with experimental EPR/ENDOR data. Hydrogen bonding and solvation affect the ferric-peroxo/ferrous-superoxo electromerism. The transition between the two electromers appears smooth, but neither hydrogen bonding to up to two water molecules, nor solvation appear able to dramatically alter the redox state of the superoxo ligand or of the iron. The presence of almost one full unpaired electron on the iron and of one full unpaired electron on the dioxygenic ligand in the "ferric-peroxo" state suggests a possible description of non-protonated "ferric-peroxo" as {ferric-superoxo+porphyrin radical}. Emerging from the DFT data is the possibility that a protonated Compound has already been detected in ENDOR experiments on cytochrome P450. The general feasibility of a protonated Compound in P450 monooxygenases is probed in light of these findings. To encompass the multiple mechanisms available in P450 for substrate oxidation, we define "mechanistic promiscuity" as the feature allowing an enzyme to perform the same reaction, with the same product, using more than one mechanism.

Few-layer MoSe₂ possessing high catalytic activity towards iodide/tri-iodide redox shuttles.

PubMed

Lee, Lawrence Tien Lin; He, Jian; Wang, Baohua; Ma, Yaping; Wong, King Young; Li, Quan; Xiao, Xudong; Chen, Tao

2014-02-14

Due to the two-dimensional confinement of electrons, single- and few-layer MoSe₂ nanostructures exhibit unusual optical and electrical properties and have found wide applications in catalytic hydrogen evolution reaction, field effect transistor, electrochemical intercalation, and so on. Here we present a new application in dye-sensitized solar cell as catalyst for the reduction of I₃(-) to I(-) at the counter electrode. The few-layer MoSe₂ is fabricated by surface selenization of Mo-coated soda-lime glass. Our results show that the few-layer MoSe₂ displays high catalytic efficiency for the regeneration of I(-) species, which in turn yields a photovoltaic energy conversion efficiency of 9.00%, while the identical photoanode coupling with "champion" electrode based on Pt nanoparticles on FTO glass generates efficiency only 8.68%. Thus, a Pt- and FTO-free counter electrode outperforming the best conventional combination is obtained. In this electrode, Mo film is found to significantly decrease the sheet resistance of the counter electrode, contributing to the excellent device performance. Since all of the elements in the electrode are of high abundance ratios, this type of electrode is promising for the fabrication of large area devices at low materials cost.

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.

Modeling the heterogeneous catalytic activity of a single nanoparticle using a first passage time distribution formalism

NASA Astrophysics Data System (ADS)

Das, Anusheela; Chaudhury, Srabanti

2015-11-01

Metal nanoparticles are heterogeneous catalysts and have a multitude of non-equivalent, catalytic sites on the nanoparticle surface. The product dissociation step in such reaction schemes can follow multiple pathways. Proposed here for the first time is a completely analytical theoretical framework, based on the first passage time distribution, that incorporates the effect of heterogeneity in nanoparticle catalysis explicitly by considering multiple, non-equivalent catalytic sites on the nanoparticle surface. Our results show that in nanoparticle catalysis, the effect of dynamic disorder is manifested even at limiting substrate concentrations in contrast to an enzyme that has only one well-defined active site.

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

PubMed

Gül, S; Eren, O; Kır, S; Onal, Y

2012-01-01

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

Nanosized iron and chromium oxides supported on mesoporous CeO2 and SBA-15 silica: Physicochemical and catalytic study

NASA Astrophysics Data System (ADS)

Tsoncheva, Tanya; Roggenbuck, Jan; Paneva, Daniela; Dimitrov, Momtchil; Mitov, Ivan; Fröba, Michael

2010-11-01

Mesoporous ceria and SBA-15 silica were modified with iron and chromium oxide nanoparticles and characterized by XRD, N2-physisorption, FTIR, UV-vis, Moessbauer spectroscopy and TPR-TG in hydrogen. Their catalytic behaviour in methanol decomposition to CO and hydrogen was also studied. Stabilization of mono- and bi-chromate species, FeOx patches or isolated iron ions as well as Fe2O3 and Cr2O3 nanoparticles in different ratio depending on the nature of the porous matrix was observed. The simultaneous presence of iron and chromium oxides lead to change in their dispersion, providing easier reducibility, higher catalytic activity and stability of the obtained materials in comparison with the corresponding mono-component ones. The "intimate contact" at the interface of both loaded metal oxide nanoparticles and the support was discussed with respect to explain the differences in the state of the active ingredient and its specific catalytic behaviour.

Evaluation of the coordination preferences and catalytic pathways of heteroaxial cobalt oximes towards hydrogen generation

DOE PAGES

Basu, Debashis; Mazumder, Shivnath; Niklas, Jens; ...

2016-02-02

Three new heteroaxial cobalt oxime catalysts, namely [Co III(prdioxH)( 4tBupy)(Cl)]PF 6 (1), [Co III(prdioxH)( 4Pyrpy)(Cl)]PF 6 (2), and [Co III(prdioxH)( 4Bzpy)(Cl)]PF 6 (3) have been studied. These species contain chloro and substituted tert-butyl/pyrrolidine/benzoyl-pyridino ligands axially coordinated to a trivalent cobalt ion bound to the N 4-oxime macrocycle (2 E,2' E,3 E,3' E)-3,3'-(propane-1,3-diylbis(azanylylidene))bis(butan-2-one)dioxime, abbreviated (prdioxH)– in its monoprotonated form. Emphasis was given to the spectroscopic investigation of the coordination preferences and spin configurations among the different 3d 6 Co III, 3d 7 Co II, and 3d 8 Co I oxidation states of the metal, and to the catalytic proton reduction withmore » an evaluation of the pathways for the generation of H 2 via Co III–H – or Co II–H – intermediates by mono and bimetallic routes. The strong field imposed by the (prdioxH)– ligand precludes the existence of high-spin configurations, and 6-coordinate geometry is favored by the LSCo III species. Species 1 and 3 show a split Co III/Co II electrochemical wave associated with partial chemical conversion to a [Co III(prdioxH)Cl 2] species, whereas 2 shows a single event. The reduction of these Co III complexes yields LSCo II and LSCo I species in which the pyridine acts as the dominant axial ligand. In the presence of protons, the catalytically active Co I species generates a Co III–H – hydride species that reacts heterolytically with another proton to generate dihydrogen. The intermediacy of a trifluoroacetate-bound Co III/Co II couple in the catalytic mechanism is proposed. Finally, these results allow for a generalization of the behavior of heteroaxial cobalt macrocycles and serve as guidelines for the development of new catalysts based on macrocyclic frameworks.« less

A Threonine Stabilizes the NiC and NiR Catalytic Intermediates of [NiFe]-hydrogenase*

PubMed Central

Abou-Hamdan, Abbas; Ceccaldi, Pierre; Lebrette, Hugo; Gutiérrez-Sanz, Oscar; Richaud, Pierre; Cournac, Laurent; Guigliarelli, Bruno; De Lacey, Antonio L.; Léger, Christophe; Volbeda, Anne; Burlat, Bénédicte; Dementin, Sébastien

2015-01-01

The heterodimeric [NiFe] hydrogenase from Desulfovibrio fructosovorans catalyzes the reversible oxidation of H2 into protons and electrons. The catalytic intermediates have been attributed to forms of the active site (NiSI, NiR, and NiC) detected using spectroscopic methods under potentiometric but non-catalytic conditions. Here, we produced variants by replacing the conserved Thr-18 residue in the small subunit with Ser, Val, Gln, Gly, or Asp, and we analyzed the effects of these mutations on the kinetic (H2 oxidation, H2 production, and H/D exchange), spectroscopic (IR, EPR), and structural properties of the enzyme. The mutations disrupt the H-bond network in the crystals and have a strong effect on H2 oxidation and H2 production turnover rates. However, the absence of correlation between activity and rate of H/D exchange in the series of variants suggests that the alcoholic group of Thr-18 is not necessarily a proton relay. Instead, the correlation between H2 oxidation and production activity and the detection of the NiC species in reduced samples confirms that NiC is a catalytic intermediate and suggests that Thr-18 is important to stabilize the local protein structure of the active site ensuring fast NiSI-NiC-NiR interconversions during H2 oxidation/production. PMID:25666617

A threonine stabilizes the NiC and NiR catalytic intermediates of [NiFe]-hydrogenase.

PubMed

Abou-Hamdan, Abbas; Ceccaldi, Pierre; Lebrette, Hugo; Gutiérrez-Sanz, Oscar; Richaud, Pierre; Cournac, Laurent; Guigliarelli, Bruno; De Lacey, Antonio L; Léger, Christophe; Volbeda, Anne; Burlat, Bénédicte; Dementin, Sébastien

2015-03-27

The heterodimeric [NiFe] hydrogenase from Desulfovibrio fructosovorans catalyzes the reversible oxidation of H2 into protons and electrons. The catalytic intermediates have been attributed to forms of the active site (NiSI, NiR, and NiC) detected using spectroscopic methods under potentiometric but non-catalytic conditions. Here, we produced variants by replacing the conserved Thr-18 residue in the small subunit with Ser, Val, Gln, Gly, or Asp, and we analyzed the effects of these mutations on the kinetic (H2 oxidation, H2 production, and H/D exchange), spectroscopic (IR, EPR), and structural properties of the enzyme. The mutations disrupt the H-bond network in the crystals and have a strong effect on H2 oxidation and H2 production turnover rates. However, the absence of correlation between activity and rate of H/D exchange in the series of variants suggests that the alcoholic group of Thr-18 is not necessarily a proton relay. Instead, the correlation between H2 oxidation and production activity and the detection of the NiC species in reduced samples confirms that NiC is a catalytic intermediate and suggests that Thr-18 is important to stabilize the local protein structure of the active site ensuring fast NiSI-NiC-NiR interconversions during H2 oxidation/production. © 2015 by The American Society for Biochemistry and Molecular Biology, Inc.

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.

Structural basis for catalytic activation by the human ZNF451 SUMO E3 ligase

DOE PAGES

Cappadocia, Laurent; Pichler, Andrea; Lima, Christopher D.

2015-11-02

E3 protein ligases enhance transfer of ubiquitin-like (Ubl) proteins from E2 conjugating enzymes to substrates by stabilizing the thioester-charged E2~Ubl in a closed configuration optimally aligned for nucleophilic attack. In this paper, we report biochemical and structural data that define the N-terminal domain of the Homo sapiens ZNF451 as the catalytic module for SUMO E3 ligase activity. The ZNF451 catalytic module contains tandem SUMO-interaction motifs (SIMs) bridged by a Pro-Leu-Arg-Pro (PLRP) motif. The first SIM and PLRP motif engage thioester-charged E2~SUMO while the next SIM binds a second molecule of SUMO bound to the back side of E2. We showmore » that ZNF451 is SUMO2 specific and that SUMO modification of ZNF451 may contribute to activity by providing a second molecule of SUMO that interacts with E2. Finally, our results are consistent with ZNF451 functioning as a bona fide SUMO E3 ligase.« less

Structural basis for catalytic activation by the human ZNF451 SUMO E3 ligase

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

Cappadocia, Laurent; Pichler, Andrea; Lima, Christopher D.

E3 protein ligases enhance transfer of ubiquitin-like (Ubl) proteins from E2 conjugating enzymes to substrates by stabilizing the thioester-charged E2~Ubl in a closed configuration optimally aligned for nucleophilic attack. In this paper, we report biochemical and structural data that define the N-terminal domain of the Homo sapiens ZNF451 as the catalytic module for SUMO E3 ligase activity. The ZNF451 catalytic module contains tandem SUMO-interaction motifs (SIMs) bridged by a Pro-Leu-Arg-Pro (PLRP) motif. The first SIM and PLRP motif engage thioester-charged E2~SUMO while the next SIM binds a second molecule of SUMO bound to the back side of E2. We showmore » that ZNF451 is SUMO2 specific and that SUMO modification of ZNF451 may contribute to activity by providing a second molecule of SUMO that interacts with E2. Finally, our results are consistent with ZNF451 functioning as a bona fide SUMO E3 ligase.« less

The Botrytis cinerea xylanase Xyn11A contributes to virulence with its necrotizing activity, not with its catalytic activity

PubMed Central

2010-01-01

Background The Botrytis cinerea xylanase Xyn11A has been previously shown to be required for full virulence of this organism despite its poor contribution to the secreted xylanase activity and the low xylan content of B. cinerea hosts. Intriguingly, xylanases from other fungi have been shown to have the property, independent of the xylan degrading activity, to induce necrosis when applied to plant tissues, so we decided to test the hypothesis that secreted Xyn11A contributes to virulence by promoting the necrosis of the plant tissue surrounding the infection, therefore facilitating the growth of this necrotroph. Results We show here that Xyn11A has necrotizing activity on plants and that this capacity is conserved in site-directed mutants of the protein lacking the catalytic activity. Besides, Xyn11A contributes to the infection process with the necrotizing and not with the xylan hydrolyzing activity, as the catalytically-impaired Xyn11A variants were able to complement the lower virulence of the xyn11A mutant. The necrotizing activity was mapped to a 30-amino acids peptide in the protein surface, and this region was also shown to mediate binding to tobacco spheroplasts by itself. Conclusions The main contribution of the xylanase Xyn11A to the infection process of B. cinerea is to induce necrosis of the infected plant tissue. A conserved 30-amino acids region on the enzyme surface, away from the xylanase active site, is responsible for this effect and mediates binding to plant cells. PMID:20184750

Complex Wall Boundary Conditions for Modeling Combustion in Catalytic Channels

NASA Astrophysics Data System (ADS)

Zhu, Huayang; Jackson, Gregory

2000-11-01

Monolith catalytic reactors for exothermic oxidation are being used in automobile exhaust clean-up and ultra-low emissions combustion systems. The reactors present a unique coupling between mass, heat, and momentum transport in a channel flow configuration. The use of porous catalytic coatings along the channel wall presents a complex boundary condition when modeled with the two-dimensional channel flow. This current work presents a 2-D transient model for predicting the performance of catalytic combustion systems for methane oxidation on Pd catalysts. The model solves the 2-D compressible transport equations for momentum, species, and energy, which are solved with a porous washcoat model for the wall boundary conditions. A time-splitting algorithm is used to separate the stiff chemical reactions from the convective/diffusive equations for the channel flow. A detailed surface chemistry mechanism is incorporated for the catalytic wall model and is used to predict transient ignition and steady-state conversion of CH4-air flows in the catalytic reactor.

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

PubMed

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

2003-09-01

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

Catalytic dehydrogenation of isobutane in the presence of hydrogen over Cs-modified Ni2P supported on active carbon

NASA Astrophysics Data System (ADS)

Xu, Yanli; Sang, Huanxin; Wang, Kang; Wang, Xitao

2014-10-01

In this article, an environmentally friendly non-noble-metal class of Cs-Ni2P/active carbon (AC) catalyst was prepared and demonstrated to exhibit enhanced catalytic performance in isobutane dehydrogenation. The results of activity tests reveal that Ni/AC catalyst was highly active for isobutane cracking, which led to the formation of abundant methane and coke. After the introduction of phosphorus through impregnation with ammonium di-hydrogen phosphate and H2-temperature programmed reduction, undesired cracking reactions were effectively inhibited, and the selectivity to isobutene and stability of catalyst increased remarkably. The characterization results indicate that, after the addition of phosphorous, the improvement of dehydrogenation selectivity is ascribed to the partial positive charges carried on Ni surface in Ni2P particles, which decreases the strength of Nisbnd C bond between Ni and carbonium-ion intermediates and the possibility of excessive dehydrogenation. In addition, Cs-modified Ni2P/AC catalysts display much higher catalytic performance as compared to Ni2P/AC catalyst. Cs-Ni2P-6.5 catalyst has the highest catalytic performance, and the selectivity to isobutene higher than 93% can be obtained even after 4 h reaction. The enhancement in catalytic performance of the Cs-modified catalysts is mainly attributed to the function of Cs to improve the dispersion of Ni2P particles, transfer electron from Cs to Ni, and decrease acid site number and strength.

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.

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

A Redox 2-Cys Mechanism Regulates the Catalytic Activity of Divergent Cyclophilins1[W

PubMed Central

Campos, Bruna Medéia; Sforça, Mauricio Luis; Ambrosio, Andre Luis Berteli; Domingues, Mariane Noronha; Brasil de Souza, Tatiana de Arruda Campos; Barbosa, João Alexandre Ribeiro Gonçalvez; Leme, Adriana Franco Paes; Perez, Carlos Alberto; Whittaker, Sara Britt-Marie; Murakami, Mario Tyago; Zeri, Ana Carolina de Matos; Benedetti, Celso Eduardo

2013-01-01

The citrus (Citrus sinensis) cyclophilin CsCyp is a target of the Xanthomonas citri transcription activator-like effector PthA, required to elicit cankers on citrus. CsCyp binds the citrus thioredoxin CsTdx and the carboxyl-terminal domain of RNA polymerase II and is a divergent cyclophilin that carries the additional loop KSGKPLH, invariable cysteine (Cys) residues Cys-40 and Cys-168, and the conserved glutamate (Glu) Glu-83. Despite the suggested roles in ATP and metal binding, the functions of these unique structural elements remain unknown. Here, we show that the conserved Cys residues form a disulfide bond that inactivates the enzyme, whereas Glu-83, which belongs to the catalytic loop and is also critical for enzyme activity, is anchored to the divergent loop to maintain the active site open. In addition, we demonstrate that Cys-40 and Cys-168 are required for the interaction with CsTdx and that CsCyp binds the citrus carboxyl-terminal domain of RNA polymerase II YSPSAP repeat. Our data support a model where formation of the Cys-40-Cys-168 disulfide bond induces a conformational change that disrupts the interaction of the divergent and catalytic loops, via Glu-83, causing the active site to close. This suggests a new type of allosteric regulation in divergent cyclophilins, involving disulfide bond formation and a loop-displacement mechanism. PMID:23709667

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.

Activation Loop Dynamics Determine the Different Catalytic Efficiencies of B Cell- and T Cell-Specific Tec Kinases

PubMed Central

Joseph, Raji E.; Kleino, Iivari; Wales, Thomas E.; Xie, Qian; Fulton, D. Bruce; Engen, John R.; Berg, Leslie J.; Andreotti, Amy H.

2014-01-01

Itk and Btk are nonreceptor tyrosine kinases of the Tec family that signal downstream of the T cell receptor (TCR) and B cell receptor (BCR), respectively. Despite their high sequence similarity and related signaling roles, Btk is a substantially more active kinase than Itk. We showed that substitution of six of the 619 amino acid residues of Itk with those of Btk was sufficient to completely switch the activities of Itk and Btk. The substitutions responsible for the swap in activity are all localized to the activation segment of the kinase domain. Nuclear magnetic resonance and hydrogen-deuterium exchange mass spectrometry analyses revealed that Itk and Btk had distinct protein dynamics in this region, which could explain the observed differences in catalytic efficiency between these kinases. Introducing Itk with enhanced activity into T cells led to enhanced and prolonged TCR signaling compared to that in cells with wild-type Itk. These findings imply that evolutionary pressures have led to Tec kinases having distinct enzymatic properties depending on the cellular context. We suggest that the weaker catalytic activities observed for T cell–specific kinases is one mechanism to regulate cellular activation and prevent aberrant immune responses. PMID:23982207

Effect of plasma-induced surface charging on catalytic processes: application to CO2 activation

NASA Astrophysics Data System (ADS)

Bal, Kristof M.; Huygh, Stijn; Bogaerts, Annemie; Neyts, Erik C.

2018-02-01

Understanding the nature and effect of the multitude of plasma-surface interactions in plasma catalysis is a crucial requirement for further process development and improvement. A particularly intriguing and rather unique property of a plasma-catalytic setup is the ability of the plasma to modify the electronic structure, and hence chemical properties, of the catalyst through charging, i.e. the absorption of excess electrons. In this work, we develop a quantum chemical model based on density functional theory to study excess negative surface charges in a heterogeneous catalyst exposed to a plasma. This method is specifically applied to investigate plasma-catalytic CO2 activation on supported M/Al2O3 (M = Ti, Ni, Cu) single atom catalysts. We find that (1) the presence of a negative surface charge dramatically improves the reductive power of the catalyst, strongly promoting the splitting of CO2 to CO and oxygen, and (2) the relative activity of the investigated transition metals is also changed upon charging, suggesting that controlled surface charging is a powerful additional parameter to tune catalyst activity and selectivity. These results strongly point to plasma-induced surface charging of the catalyst as an important factor contributing to the plasma-catalyst synergistic effects frequently reported for plasma catalysis.

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

PubMed

Furuya, Toshiki; Kino, Kuniki

2014-02-01

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

Effects of Coke Deposits on the Catalytic Performance of Large Zeolite H-ZSM-5 Crystals during Alcohol-to-Hydrocarbon Reactions as Investigated by a Combination of Optical Spectroscopy and Microscopy

PubMed Central

Nordvang, Emily C; Borodina, Elena; Ruiz-Martínez, Javier; Fehrmann, Rasmus; Weckhuysen, Bert M

2015-01-01

The catalytic activity of large zeolite H-ZSM-5 crystals in methanol (MTO) and ethanol-to-olefins (ETO) conversions was investigated and, using operando UV/Vis measurements, the catalytic activity and deactivation was correlated with the formation of coke. These findings were related to in situ single crystal UV/Vis and confocal fluorescence micro-spectroscopy, allowing the observation of the spatiotemporal formation of intermediates and coke species during the MTO and ETO conversions. It was observed that rapid deactivation at elevated temperatures was due to the fast formation of aromatics at the periphery of the H-ZSM-5 crystals, which are transformed into more poly-aromatic coke species at the external surface, preventing the diffusion of reactants and products into and out of the H-ZSM-5 crystal. Furthermore, we were able to correlate the operando UV/Vis spectroscopy results observed during catalytic testing with the single crystal in situ results. PMID:26463581

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.

Impact of orientation of carbohydrate binding modules family 22 and 6 on the catalytic activity of Thermotoga maritima xylanase XynB.

PubMed

Tajwar, Razia; Shahid, Saher; Zafar, Rehan; Akhtar, Muhammad Waheed

2017-11-01

Xylanase XynB of the hyperthermophile Thermotoga maritima, which belongs to glycoside hydrolase family 10 (GH10), does not have an associated carbohydrate binding module (CBM) in the native state. CBM6 and CBM22 from a thermophile Clostridium thermocellum were fused to the catalytic domain of XynB (XynB-C) to determine the effects on activity and other properties. XynB-B22C and XynB-CB22, produced by fusing CBM22 to the N- and C-terminal of XynB-C, showed 1.7- and 3.24-fold increase in activity against the insoluble birchwood xylan, respectively. Similarly, CBM6 when attached to the C-terminal of XynB-C resulted in 2.0-fold increase in activity, whereas its attachment to the N-terminal did not show any increase of activity. XynB-B22C and XynB-CB22 retained all the activity, whereas XynB-B6C and XynB-CB6 lost 17 and 11% of activity, respectively, at 60°C for 4h. Thermostability data and the secondary structure contents obtained by molecular modelling are in agreement with the data from circular dichroism analysis. Molecular modelling analysis showed that the active site residues of the catalytic domain and the binding residues of CBM6 and CBM22 were located on the surface of molecule, except XynB-B6C, where the binding residues were found somewhat buried. In the case of XynB-CB22, the catalytic and the binding residues seem to be located favorably adjacent to each other, thus showing higher increase in activity. This study shows that the active site residues of the catalytic domain and the binding residues of the CBM are arranged in a unique fashion, not reported before. Copyright © 2017 Elsevier Inc. All rights reserved.

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.

Contributions of phase, sulfur vacancies, and edges to the hydrogen evolution reaction catalytic activity of porous molybdenum disulfide nanosheets

DOE PAGES

Yin, Ying; Han, Jiecai; Zhang, Yumin; ...

2016-06-07

Molybdenum disulfide (MoS 2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS 2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS 2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS 2 nanosheet samples, including 2H and 1T phase, porous 2H andmore » 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS 2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS 2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS 2 always outperforms the corresponding 2H phase MoS 2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS 2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. Furthermore, this study presents new insights and opens up new avenues for designing electrocatalysts based on MoS 2 or other layered materials with enhanced HER performance.« less

Contributions of phase, sulfur vacancies, and edges to the hydrogen evolution reaction catalytic activity of porous molybdenum disulfide nanosheets

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

Yin, Ying; Han, Jiecai; Zhang, Yumin

Molybdenum disulfide (MoS 2) is a promising nonprecious catalyst for the hydrogen evolution reaction (HER) that has been extensively studied due to its excellent performance, but the lack of understanding of the factors that impact its catalytic activity hinders further design and enhancement of MoS 2-based electrocatalysts. Here, by using novel porous (holey) metallic 1T phase MoS 2 nanosheets synthesized by a liquid-ammonia-assisted lithiation route, we systematically investigated the contributions of crystal structure (phase), edges, and sulfur vacancies (S-vacancies) to the catalytic activity toward HER from five representative MoS 2 nanosheet samples, including 2H and 1T phase, porous 2H andmore » 1T phase, and sulfur-compensated porous 2H phase. Superior HER catalytic activity was achieved in the porous 1T phase MoS 2 nanosheets that have even more edges and S-vacancies than conventional 1T phase MoS 2. A comparative study revealed that the phase serves as the key role in determining the HER performance, as 1T phase MoS 2 always outperforms the corresponding 2H phase MoS 2 samples, and that both edges and S-vacancies also contribute significantly to the catalytic activity in porous MoS 2 samples. Then, using combined defect characterization techniques of electron spin resonance spectroscopy and positron annihilation lifetime spectroscopy to quantify the S-vacancies, the contributions of each factor were individually elucidated. Furthermore, this study presents new insights and opens up new avenues for designing electrocatalysts based on MoS 2 or other layered materials with enhanced HER performance.« less

Catalytic destruction of groundwater contaminants in reactive extraction wells

DOEpatents

McNab, Jr., Walt W.; Reinhard, Martin

2002-01-01

A system for remediating groundwater contaminated with halogenated solvents, certain metals and other inorganic species based on catalytic reduction reactions within reactive well bores. The groundwater treatment uses dissolved hydrogen as a reducing agent in the presence of a metal catalyst, such a palladium, to reduce halogenated solvents (as well as other substituted organic compounds) to harmless species (e.g., ethane or methane) and immobilize certain metals to low valence states. The reactive wells function by removing water from a contaminated water-bearing zone, treating contaminants with a well bore using catalytic reduction, and then reinjecting the treated effluent into an adjacent water-bearing zone. This system offers the advantages of a compact design with a minimal surface footprint (surface facilities) and the destruction of a broad suite of contaminants without generating secondary waste streams.

An Analytical Framework for Studying Small-Number Effects in Catalytic Reaction Networks: A Probability Generating Function Approach to Chemical Master Equations

PubMed Central

Nakagawa, Masaki; Togashi, Yuichi

2016-01-01

Cell activities primarily depend on chemical reactions, especially those mediated by enzymes, and this has led to these activities being modeled as catalytic reaction networks. Although deterministic ordinary differential equations of concentrations (rate equations) have been widely used for modeling purposes in the field of systems biology, it has been pointed out that these catalytic reaction networks may behave in a way that is qualitatively different from such deterministic representation when the number of molecules for certain chemical species in the system is small. Apart from this, representing these phenomena by simple binary (on/off) systems that omit the quantities would also not be feasible. As recent experiments have revealed the existence of rare chemical species in cells, the importance of being able to model potential small-number phenomena is being recognized. However, most preceding studies were based on numerical simulations, and theoretical frameworks to analyze these phenomena have not been sufficiently developed. Motivated by the small-number issue, this work aimed to develop an analytical framework for the chemical master equation describing the distributional behavior of catalytic reaction networks. For simplicity, we considered networks consisting of two-body catalytic reactions. We used the probability generating function method to obtain the steady-state solutions of the chemical master equation without specifying the parameters. We obtained the time evolution equations of the first- and second-order moments of concentrations, and the steady-state analytical solution of the chemical master equation under certain conditions. These results led to the rank conservation law, the connecting state to the winner-takes-all state, and analysis of 2-molecules M-species systems. A possible interpretation of the theoretical conclusion for actual biochemical pathways is also discussed. PMID:27047384

Facile synthesis of pristine graphene-palladium nanocomposites with extraordinary catalytic activities using swollen liquid crystals

NASA Astrophysics Data System (ADS)

Vats, T.; Dutt, S.; Kumar, R.; Siril, P. F.

2016-09-01

Amazing conductivity, perfect honeycomb sp2 arrangement and the high theoretical surface area make pristine graphene as one of the best materials suited for application as catalyst supports. Unfortunately, the low reactivity of the material makes the formation of nanocomposite with inorganic materials difficult. Here we report an easy approach to synthesize nanocomposites of pristine graphene with palladium (Pd-G) using swollen liquid crystals (SLCs) as a soft template. The SLC template gives the control to deposit very small Pd particles of uniform size on G as well as RGO. The synthesized nanocomposite (Pd-G) exhibited exceptionally better catalytic activity compared with Pd-RGO nanocomposite in the hydrogenation of nitrophenols and microwave assisted C-C coupling reactions. The catalytic activity of Pd-G nanocomposite during nitrophenol reduction reaction was sixteen times higher than Pd nanoparticles and more than double than Pd-RGO nanocomposite. The exceptionally high activity of pristine graphene supported catalysts in the organic reactions is explained on the basis of its better pi interacting property compared to partially reduced RGO. The Pd-G nanocomposite showed exceptional stability under the reaction conditions as it could be recycled upto a minimum of 15 cycles for the C-C coupling reactions without any loss in activity.

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.

Solid state oxygen anion and electron mediating membrane and catalytic membrane reactors containing them

DOEpatents

Schwartz, Michael; White, James H.; Sammells, Anthony F.

2005-09-27

This invention relates to gas-impermeable, solid state materials fabricated into membranes for use in catalytic membrane reactors. This invention particularly relates to solid state oxygen anion- and electron-mediating membranes for use in catalytic membrane reactors for promoting partial or full oxidation of different chemical species, for decomposition of oxygen-containing species, and for separation of oxygen from other gases. Solid state materials for use in the membranes of this invention include mixed metal oxide compounds having the brownmillerite crystal structure.

Solid state oxygen anion and electron mediating membrane and catalytic membrane reactors containing them

DOEpatents

Schwartz, Michael; White, James H.; Sammels, Anthony F.

2000-01-01

This invention relates to gas-impermeable, solid state materials fabricated into membranes for use in catalytic membrane reactors. This invention particularly relates to solid state oxygen anion- and electron-mediating membranes for use in catalytic membrane reactors for promoting partial or full oxidation of different chemical species, for decomposition of oxygen-containing species, and for separation of oxygen from other gases. Solid state materials for use in the membranes of this invention include mixed metal oxide compounds having the brownmillerite crystal structure.

Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

NASA Astrophysics Data System (ADS)

Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

2016-08-01

Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size.

Preparation and Catalytic Activity for Aerobic Glucose Oxidation of Crown Jewel Structured Pt/Au Bimetallic Nanoclusters

PubMed Central

Zhang, Haijun; Wang, Liqiong; Lu, Lilin; Toshima, Naoki

2016-01-01

Understanding of the “structure-activity” relations for catalysts at an atomic level has been regarded as one of the most important objectives in catalysis studies. Bimetallic nanoclusters (NCs) in its many types, such as core/shell, random alloy, cluster-in-cluster, bi-hemisphere, and crown jewel (one kind of atom locating at the top position of another kind of NC), attract significant attention owing to their excellent optical, electronic, and catalytic properties. PVP-protected crown jewel-structured Pt/Au (CJ-Pt/Au) bimetallic nanoclusters (BNCs) with Au atoms located at active top sites were synthesized via a replacement reaction using 1.4-nm Pt NCs as mother clusters even considering the fact that the replacement reaction between Pt and Au3+ ions is difficult to be occurred. The prepared CJ-Pt/Au colloidal catalysts characterized by UV-Vis, TEM, HR-TEM and HAADF-STEM-EELS showed a high catalytic activity for aerobic glucose oxidation, and the top Au atoms decorating the Pt NCs were about 15 times more active than the Au atoms of Au NCs with similar particle size. PMID:27476577

Native Electrophoresis-Coupled Activity Assays Reveal Catalytically-Active Protein Aggregates of Escherichia coli β-Glucuronidase

PubMed Central

Burchett, Gina G.; Folsom, Charles G.; Lane, Kimberly T.

2015-01-01

β-glucuronidase is found as a functional homotetramer in a variety of organisms, including humans and other animals, as well as a number of bacteria. This enzyme is important in these organisms, catalyzing the hydrolytic removal of a glucuronide moiety from substrate molecules. This process serves to break down sugar conjugates in animals and provide sugars for metabolism in bacteria. While β-glucuronidase is primarily found as a homotetramer, previous studies have indicated that the human form of the protein is also catalytically active as a dimer. Here we present evidence for not only an active dimer of the E. coli form of the protein, but also for several larger active complexes, including an octomer and a 16-mer. Additionally, we propose a model for the structures of these large complexes, based on computationally-derived molecular modeling studies. These structures may have application in the study of human disease, as several diseases have been associated with the aggregation of proteins. PMID:26121040

Native Electrophoresis-Coupled Activity Assays Reveal Catalytically-Active Protein Aggregates of Escherichia coli β-Glucuronidase.

PubMed

Burchett, Gina G; Folsom, Charles G; Lane, Kimberly T

2015-01-01

β-glucuronidase is found as a functional homotetramer in a variety of organisms, including humans and other animals, as well as a number of bacteria. This enzyme is important in these organisms, catalyzing the hydrolytic removal of a glucuronide moiety from substrate molecules. This process serves to break down sugar conjugates in animals and provide sugars for metabolism in bacteria. While β-glucuronidase is primarily found as a homotetramer, previous studies have indicated that the human form of the protein is also catalytically active as a dimer. Here we present evidence for not only an active dimer of the E. coli form of the protein, but also for several larger active complexes, including an octomer and a 16-mer. Additionally, we propose a model for the structures of these large complexes, based on computationally-derived molecular modeling studies. These structures may have application in the study of human disease, as several diseases have been associated with the aggregation of proteins.

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.

The Impact of the Polymer Chain Length on the Catalytic Activity of Poly(N-vinyl-2-pyrrolidone)-supported Gold Nanoclusters.

PubMed

Haesuwannakij, Setsiri; Kimura, Tetsunari; Furutani, Yuji; Okumura, Kazu; Kokubo, Ken; Sakata, Takao; Yasuda, Hidehiro; Yakiyama, Yumi; Sakurai, Hidehiro

2017-08-29

Poly(N-vinyl-2-pyrrolidone) (PVP) of varying molecular weight (M w  = 40-360 kDa) were employed to stabilize gold nanoclusters of varying size. The resulting Au:PVP clusters were subsequently used as catalysts for a kinetic study on the sized-dependent aerobic oxidation of 1-indanol, which was monitored by time-resolved in situ infrared spectroscopy. The obtained results suggest that the catalytic behaviour is intimately correlated to the size of the clusters, which in turn depends on the molecular weight of the PVPs. The highest catalytic activity was observed for clusters with a core size of ~7 nm, and the size of the cluster should increase with the molecular weight of the polymer in order to maintain optimal catalytic activity. Studies on the electronic and colloid structure of these clusters revealed that the negative charge density on the cluster surface also strongly depends on the molecular weight of the stabilizing polymers.

Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation

PubMed Central

2011-01-01

In this article, PtAg alloy nanoislands/graphene hybrid composites were prepared based on the self-organization of Au@PtAg nanorods on graphene sheets. Graphite oxides (GO) were prepared and separated to individual sheets using Hummer's method. Graphene nano-sheets were prepared by chemical reduction with hydrazine. The prepared PtAg alloy nanomaterial and the hybrid composites with graphene were characterized by SEM, TEM, and zeta potential measurements. It is confirmed that the prepared Au@PtAg alloy nanorods/graphene hybrid composites own good catalytic function for methanol electro-oxidation by cyclic voltammograms measurements, and exhibited higher catalytic activity and more stability than pure Au@Pt nanorods and Au@AgPt alloy nanorods. In conclusion, the prepared PtAg alloy nanoislands/graphene hybrid composites own high stability and catalytic activity in methanol electro-oxidation, so that it is one kind of high-performance catalyst, and has great potential in applications such as methanol fuel cells in near future. PMID:21982417

Shape-dependent plasma-catalytic activity of ZnO nanomaterials coated on porous ceramic membrane for oxidation of butane.

PubMed

Sanjeeva Gandhi, M; Mok, Young Sun

2014-12-01

In order to explore the effects of the shape of ZnO nanomaterials on the plasma-catalytic decomposition of butane and the distribution of byproducts, three types of ZnO nanomaterials (nanoparticles (NPs), nanorods (NRs) and nanowires (NWs)) were prepared and coated on multi-channel porous alumina ceramic membrane. The structures and morphologies of the nanomaterials were confirmed by X-ray diffraction method and scanning electron microscopy. The observed catalytic activity of ZnO in the oxidative decomposition of butane was strongly shape-dependent. It was found that the ZnO NWs exhibited higher catalytic activity than the other nanomaterials and could completely oxidize butane into carbon oxides (COx). When using the bare or ZnO NPs-coated ceramic membrane, several unwanted partial oxidation and decomposition products like acetaldehyde, acetylene, methane and propane were identified during the decomposition of butane. When the ZnO NWs- or ZnO NRs-coated membrane was used, however, the formation of such unwanted byproducts except methane was completely avoided, and full conversion into COx was achieved. Better carbon balance and COx selectivity were obtained with the ZnO NWs and NRs than with the NPs. Copyright © 2014 Elsevier Ltd. All rights reserved.

Preparation and catalytic activities of LaFeO3 and Fe2O3 for HMX thermal decomposition.

PubMed

Wei, Zhi-Xian; Xu, Yan-Qing; Liu, Hai-Yan; Hu, Chang-Wen

2009-06-15

Perovskite-type LaFeO(3) and alpha-Fe(2)O(3) with high specific surface areas were directly prepared with appropriate stearic acid-nitrates ratios by a novel stearic acid solution combustion method. The obtained powders were characterized by XRD, FT-IR and XPS techniques. The catalytic activities of perovskite-type LaFeO(3) and alpha-Fe(2)O(3) for the thermal decomposition of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) were investigated by TG and TG-EGA techniques. The experimental results show that the catalytic activity of perovskite-type LaFeO(3) was much higher than that of alpha-Fe(2)O(3) because of higher concentration of surface-adsorbed oxygen (O(ad)) and hydroxyl of LaFeO(3). The study points out a potential way to develop new and more active perovskite-type catalysts for the HMX thermal decomposition.

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.

Quantitative evaluation of hepatic cytochrome P4501A transcript, protein, and catalytic activity in the striped sea bream (Lithognathus mormyrus).

PubMed

Tom, Moshe; Shmul, Merav; Shefer, Edna; Chen, Nir; Slor, Hanoch; Rinkevich, Baruch; Herut, Barak

2003-09-01

Hepatic cytochrome P4501A (CYP1A) expression was partially characterized in the striped sea bream (Lithognathus mormyrus) from the Mediterranean coast of Israel as part of the process of establishing the CYP1A gene as an environmental biomarker. Reverse transcription-competitive polymerase chain reaction, competitive enzyme-linked immunosorbent assay, and ethoxyresorufin O-deethylase (EROD) assay were used for evaluating transcript, protein, and catalytic activity levels, respectively, in absolute units. Highest elucidated transcript, protein, and catalytic activity levels were 0.264 +/- SD 0.084 fmol/microg total RNA, 0.88 +/- 0.52 pmol/microg total protein, and 1.11 +/- 0.52 pmol resorufin/min/microg total protein, respectively, and the lower levels were 0.009 +/- 0.007 fmol/microg total RNA, 0.17 +/- 0.08 pmol/microg total protein, and 0.11 +/- 0.06 pmol resorufin/min/microg total protein, respectively, demonstrating substantial induction potential. All alternate pairs of seven examined field samples, revealing a transcript-level ratio higher than 1.7, also demonstrated a significant difference between their transcript levels, indicating a potential to detect relatively small biomarker changes (1.7-fold) caused by environmental effects. Simultaneous triple measurements of transcript, protein, and catalytic activity were carried out in individuals from two field samples and during a 318-d decay experiment. Fish from the field samples revealed significant alternate bivariate correlation between transcript, protein, and enzymatic activity. Conflicting results were found when analyzing the decay experiment, in which both protein and catalytic activity levels decreased significantly to basal levels, in contrast to no significant change in transcript levels throughout the experiment. No significant difference was observed between males and females regarding the levels of CYP1A transcript, protein, and EROD.

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.

Catalytic activity of Pd-doped Cu nanoparticles for hydrogenation as a single-atom-alloy catalyst.

PubMed

Cao, Xinrui; Fu, Qiang; Luo, Yi

2014-05-14

The single atom alloy of extended surfaces is known to provide remarkably enhanced catalytic performance toward heterogeneous hydrogenation. Here we demonstrate from first principles calculations that this approach can be extended to nanostructures, such as bimetallic nanoparticles. The catalytic properties of the single-Pd-doped Cu55 nanoparticles have been systemically examined for H2 dissociation as well as H atom adsorption and diffusion, following the concept of single atom alloy. It is found that doping a single Pd atom at the edge site of the Cu55 shell can considerably reduce the activation energy of H2 dissociation, while the single Pd atom doped at the top site or in the inner layers is much less effective. The H atom adsorption on Cu55 is slightly stronger than that on the Cu(111) surface; however, a larger nanoparticle that contains 147 atoms could effectively recover the weak binding of the H atoms. We have also investigated the H atom diffusion on the 55-atom nanoparticle and found that spillover of the produced H atoms could be a feasible process due to the low diffusion barriers. Our results have demonstrated that facile H2 dissociation and weak H atom adsorption could be combined at the nanoscale. Moreover, the effects of doping one more Pd atom on the H2 dissociation and H atom adsorption have also been investigated. We have found that both the doping Pd atoms in the most stable configuration could independently exhibit their catalytic activity, behaving as two single-atom-alloy catalysts.

Antibacterial and catalytic activities of green synthesized silver nanoparticles.

PubMed

Bindhu, M R; Umadevi, M

2015-01-25

The aqueous beetroot extract was used as reducing agent for silver nanoparticles synthesis. The synthesized nanoparticles were characterized using UV-visible spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The surface plasmon resonance peak of synthesized nanoparticles was observed at 438 nm. As the concentration of beetroot extract increases, absorption spectra shows blue shift with decreasing particle size. The prepared silver nanoparticles were well dispersed, spherical in shape with the average particle size of 15 nm. The prepared silver nanoparticles are effective in inhibiting the growth of both gram positive and gram negative bacteria. The prepared silver nanoparticles reveal faster catalytic activity. This natural method for synthesis of silver nanoparticles offers a valuable contribution in the area of green synthesis and nanotechnology avoiding the presence of hazardous and toxic solvents and waste. Copyright © 2014 Elsevier B.V. All rights reserved.

Process for catalytically oxidizing cycloolefins, particularly cyclohexene

DOEpatents

Mizuno, Noritaka; Lyon, David K.; Finke, Richard G.

1993-01-01

This invention is a process for catalytically oxidizing cycloolefins, particularly cyclohexenes, to form a variety of oxygenates. The catalyst used in the process is a covalently bonded iridium-heteropolyanion species. The process uses the catalyst in conjunction with a gaseous oxygen containing gas to form 2-cyclohexen-1-ol and also 2-cyclohexen-1-one.

Catalytic performance of heterogeneous Rh/C3N4 for the carbonylation of methanol

NASA Astrophysics Data System (ADS)

Budiman, Anatta Wahyu; Choi, Myoung Jae; Nur, Adrian

2018-02-01

The excess of water in homogeneous the carbonylation of methanol system could increase the amount of by-products formed through water-gas shift reaction and could accelerate the rusting of equipment. Many scientists tried to decrease the content of water in the carbonylation of methanol system by using lithium and iodide promoter that results a moderate catalytic activity in the water content at 2wt%. The heterogenized catalyst offers several distinct advantages such as it was enables increased catalyst concentration in the reaction mixture, which is directly proportional to acetic acid production rate, without the addition of an alkali iodide salt promoter. The heterogeneous catalyst also results in reduced by-product formation. This study is aimed to produce a novel catalyst (Rh/C3N4) with a high selectivity of acetic acid in a relatively lower water and halide content. This novel catalyst performs high conversion and selectivity of acetic acid as the result of the strong ionic bonding of melamine and rhodium complex species that was caused by the presence of methyl iodide species. The CO2 in feed gas significantly decreases the catalytic activity of Rh-melamine because of its inert characteristics. The kinetic test was performed as that the first order kinetic equation. The kinetic tests revealed the reaction route of the the carbonylation of methanol in this system was performed trough the methyl acetate.

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.

Silver nanocluster catalytic microreactors for water purification

NASA Astrophysics Data System (ADS)

Da Silva, B.; Habibi, M.; Ognier, S.; Schelcher, G.; Mostafavi-Amjad, J.; Khalesifard, H. R. M.; Tatoulian, M.; Bonn, D.

2016-07-01

A new method for the elaboration of a novel type of catalytic microsystem with a high specific area catalyst is developed. A silver nanocluster catalytic microreactor was elaborated by doping a soda-lime glass with a silver salt. By applying a high power laser beam to the glass, silver nanoclusters are obtained at one of the surfaces which were characterized by BET measurements and AFM. A microfluidic chip was obtained by sealing the silver coated glass with a NOA 81 microchannel. The catalytic activity of the silver nanoclusters was then tested for the efficiency of water purification by using catalytic ozonation to oxidize an organic pollutant. The silver nanoclusters were found to be very stable in the microreactor and efficiently oxidized the pollutant, in spite of the very short residence times in the microchannel. This opens the way to study catalytic reactions in microchannels without the need of introducing the catalyst as a powder or manufacturing complex packed bed microreactors.

Development and evaluation of kinetic spectrophotometric assays for horseradish peroxidase by catalytic coupling of paraphenylenediamine and mequinol.

PubMed

Nagaraja, Padmarajaiah; Shivakumar, Anantharaman; Kumar Shrestha, Ashwinee

2009-10-01

This paper presents a novel spectrophotometric method to measure peroxidase activity using paraphenylenediamine dihydrochloride (PPDD) and Mequinol (MQ). The PPDD traps the free radical, and gets oxidized to electrophilic 1,4-diimine; this couples with MQ to an give intense violet-colored chromogenic species with the maximum absorbance at 560 nm. This assay was adopted for the quantification of hydrogen peroxide between 10 x 10(-6) to 80 x 10(-6) M. From the kinetic data, a two-substrate ping-pong mechanism of peroxidase was established. Catalytic efficiency and catalytic power of commercial peroxidase were 0.204 x 10(6) M(-1) min(-1) and 2.86 x 10(-4) min(-1), respectively. The catalytic constant (k(cat)) of the proposed method was 0.2080 x 10(3) min(-1). As a simple, rapid, precise and sensitive technique, PPDD-MQ stands as a potential replacement for the traditional guaiacol method. Applications to the plant extracts increase its relevance in the field of biochemical analysis.

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

PubMed

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

2008-06-01

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

Application of BiFeO3-based on nickel foam composites with a highly efficient catalytic activity and easily recyclable in Fenton-like process under microwave irradiation

NASA Astrophysics Data System (ADS)

Li, Shuo; Zhang, Guangshan; Zheng, Heshan; Zheng, Yongjie; Wang, Peng

2018-05-01

In this study, BiFeO3 (BFO) powders decorated on nickel foam (NF) with a high catalytic activity are prepared via a one-step microwave-assisted hydrothermal method. The factors that influence the degradation of bisphenol A (BPA) with BFO/NFs as catalysts are optimized to improve the catalytic activity in a microwave-enhanced Fenton-like process. BFO/NF exhibit a superior catalytic activity with a high BPA removal ratio (98.4%) and TOC removal ratio (69.5%) within 5 min. Results indicate that NF significantly affect the improvement of the catalytic activity of BFO because it served as a source of hydroxyl radicals (•OH) during degradation. The amount of •OH generated by BFO/NF is approximately 1.65-fold higher than that by pure BFO. After six reaction cycles, the stability and reusability of •OH remain high. These findings provide new insights into the synthesis of composites on heterogeneous catalysts with high efficiency and easy recyclability for water treatment applications.

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.

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.

Synthesis, structural properties and catalytic activity of MgO-SnO2 nanocatalysts

NASA Astrophysics Data System (ADS)

Perveen, Hina; Farrukh, Muhammad Akhyar; Khaleeq-ur-Rahman, Muhammad; Munir, Badar; Tahir, Muhammad Ashraf

2015-01-01

Surfactant controlled synthesis of magnesium oxide-tin oxide (MgO-SnO2) nanocatalysts was carried out via the hydrothermal method. Concentration of sodium dodecyl sulfate (SDS) was varied while all other reaction conditions were kept constant same for this purpose. Furthermore, MgO-SnO2 nanocatalysts were also prepared by changing the precursor's concentration. These precursors are magnesium nitrate Mg(NO3)2 · 6H2O and tin chloride (SnCl4 · 5H2O). The influence of these reaction parameters on the sizes and morphology of the nanocatalysts were studied by using Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy-Energy dispersive X-ray (SEM-EDX), Powder X-ray diffraction (XRD), Transmission electron microscopy and Thermo gravimetric analysis (TGA). The catalytic efficiency of MgO-SnO2 was checked against 2,4-dinitrophenylhydrazine (DNPH), which is an explosive compound. The nanocatalysts were found as a good catalyst to degrade the DNPH. Catalytic activity of nanocatalysts was observed up to 19.13% for the degradation DNPH by using UV-spectrophotometer.

Sulfur doped reduced graphene oxides with enhanced catalytic activity for oxygen reduction via molten salt redox-sulfidation.

PubMed

Gu, Yuxing; Chen, Zhigang; Tang, Juanjuan; Xiao, Wei; Mao, Xuhui; Zhu, Hua; Wang, Dihua

2016-12-07

A spontaneous redox reaction of reduced graphene oxide (rGO) in molten Li 2 CO 3 -Na 2 CO 3 -K 2 CO 3 with a small amount of Li 2 SO 4 at 550 °C was applied to synthesize sulfur and sulfur-cobalt doped rGOs (S-rGO/S-Co-rGO). The obtained S-rGOs and S-Co-rGOs show enhanced catalytic activity for the oxygen reduction reaction (ORR) in alkaline aqueous solutions. The onset reduction potential and the half-wave potential of S-Co-rGO are 60 and 40 mV more positive than those of the original rGO, respectively. The reduction current density of S-Co-rGO increases by nearly five times. This study provides a green and continuous molten salt doping approach for the fabrication of heteroatom-doped graphene with excellent catalytic activity for the ORR.

Sodium-promoted Pd/TiO2 for catalytic oxidation of formaldehyde at ambient temperature.

PubMed

Zhang, Changbin; Li, Yaobin; Wang, Yafei; He, Hong

2014-05-20

Catalytic oxidation of formaldehyde (HCHO) to CO2 at ambient conditions is of great interest for indoor HCHO purification. Here, we report that sodium-doped Pd/TiO2 is a highly effective catalyst for the catalytic oxidation of HCHO at room temperature. It was observed that Na doping has a dramatic promotion effect on the Pd/TiO2 catalyst and that nearly 100% HCHO conversion could be achieved over the 2Na-Pd/TiO2 catalyst at a GHSV of 95000 h(-1) and HCHO inlet concentration of 140 ppm at 25 °C. The mechanism of the Na-promotion effect was investigated by using Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), CO chemisorption, Temperature-programmed reduction by H2 (H2-TPR), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption of O2 (O2-TPD) methods. The results showed that Na species addition can induce and further stabilize a negatively charged and well-dispersed Pd species, which then facilitates the activation of H2O and chemisorbed oxygen, therefore resulting in the high performance of the 2Na-Pd/TiO2 catalyst for the ambient HCHO destruction.

Turning Biodiesel Waste Glycerol into 1,3-Propanediol: Catalytic Performance of Sulphuric acid-Activated Montmorillonite Supported Platinum Catalysts in Glycerol Hydrogenolysis.

PubMed

Samudrala, Shanthi Priya; Kandasamy, Shalini; Bhattacharya, Sankar

2018-05-10

Direct C-O hydrogenolysis of bioglycerine to produce 1,3-propanediol selectively is a vital technology that can expand the scope of biodiesel industry and green chemical production from biomass. Herein we report sulphuric acid-activated montmorillonite clay supported platinum nanoparticles as highly effective solid acid catalysts for the selective production of 1,3-propanediol from glycerol. The catalytic performances of the catalysts were investigated in the hydrogenolysis of glycerol with a fixed bed reactor under ambient pressure. The results were found promising and showed that the activation of montmorillonite by sulphuric acid incorporated Brønsted acidity in the catalyst and significantly improved the selectivity to 1,3-propanediol. The catalytic performance of different platinum loaded catalysts was examined and 2 wt% Pt/S-MMT catalyst presented superior activity among others validating 62% 1,3-propanediol selectivity at 94% glycerol conversion. The catalytic activity of 2Pt/S-MMT was systematically investigated under varying reaction parameters including reaction temperature, hydrogen flow rate, glycerol concentration, weight hourly space velocity, and contact time to derive the optimum conditions for the reaction. The catalyst stability, reusability and structure-activity correlation were also elucidated. The high performance of the catalyst could be ascribed to well disperse Pt nanoparticles immobilized on acid-activated montmorillonite, wider pore-structure and appropriate acid sites of the catalyst.

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

Catalytic Activity of Silicon Nanowires Decorated with Gold and Copper Nanoparticles Deposited by Pulsed Laser Ablation

PubMed Central

Casiello, Michele; Fusco, Caterina; Irrera, Alessia; Trusso, Sebastiano; Cotugno, Pietro

2018-01-01

Silicon nanowires (SiNWs) decorated by pulsed laser ablation with gold or copper nanoparticles (labeled as AuNPs@SiNWs and CuNPs@SiNWs) were investigated for their catalytic properties. Results demonstrated high catalytic performances in the Caryl–N couplings and subsequent carbonylations for gold and copper catalysts, respectively, that have no precedents in the literature. The excellent activity, attested by the very high turn over number (TON) values, was due both to the uniform coverage along the NW length and to the absence of the chemical shell surrounding the metal nanoparticles (MeNPs). A high recyclability was also observed and can be ascribed to the strong covalent interaction at the Me–Si interface by virtue of metal “silicides” formation. PMID:29385761

Catalytic Activity of Silicon Nanowires Decorated with Gold and Copper Nanoparticles Deposited by Pulsed Laser Ablation.

PubMed

Casiello, Michele; Picca, Rosaria Anna; Fusco, Caterina; D'Accolti, Lucia; Leonardi, Antonio Alessio; Lo Faro, Maria Josè; Irrera, Alessia; Trusso, Sebastiano; Cotugno, Pietro; Sportelli, Maria Chiara; Cioffi, Nicola; Nacci, Angelo

2018-01-30

Silicon nanowires (SiNWs) decorated by pulsed laser ablation with gold or copper nanoparticles (labeled as AuNPs@SiNWs and CuNPs@SiNWs) were investigated for their catalytic properties. Results demonstrated high catalytic performances in the C aryl -N couplings and subsequent carbonylations for gold and copper catalysts, respectively, that have no precedents in the literature. The excellent activity, attested by the very high turn over number (TON) values, was due both to the uniform coverage along the NW length and to the absence of the chemical shell surrounding the metal nanoparticles (MeNPs). A high recyclability was also observed and can be ascribed to the strong covalent interaction at the Me-Si interface by virtue of metal "silicides" formation.

Iron piano-stool complexes containing NHC ligands outfitted with pendent arms: synthesis, characterization, and screening for catalytic transfer hydrogenation

Treesearch

Parthapratim Das; Thomas Elder; William W. Brennessel; Stephen C. Chmely

2016-01-01

Catalysis is a fundamental technology that is widely used in the food, petrochemical, pharmaceutical, and agricultural sectors to produce chemical products on an industrial scale. Well-defined molecular organometallic species are a cornerstone of catalytic methodology, and the activity and selectivity of these complexes can be modulated by judicious choice of metal and...

Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

NASA Astrophysics Data System (ADS)

Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

2016-02-01

Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion

PubMed Central

Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W.; Liu, Yan; Walter, Nils G.; Yan, Hao

2016-01-01

Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology. PMID:26861509

Nanocaged enzymes with enhanced catalytic activity and increased stability against protease digestion.

PubMed

Zhao, Zhao; Fu, Jinglin; Dhakal, Soma; Johnson-Buck, Alexander; Liu, Minghui; Zhang, Ting; Woodbury, Neal W; Liu, Yan; Walter, Nils G; Yan, Hao

2016-02-10

Cells routinely compartmentalize enzymes for enhanced efficiency of their metabolic pathways. Here we report a general approach to construct DNA nanocaged enzymes for enhancing catalytic activity and stability. Nanocaged enzymes are realized by self-assembly into DNA nanocages with well-controlled stoichiometry and architecture that enabled a systematic study of the impact of both encapsulation and proximal polyanionic surfaces on a set of common metabolic enzymes. Activity assays at both bulk and single-molecule levels demonstrate increased substrate turnover numbers for DNA nanocage-encapsulated enzymes. Unexpectedly, we observe a significant inverse correlation between the size of a protein and its activity enhancement. This effect is consistent with a model wherein distal polyanionic surfaces of the nanocage enhance the stability of active enzyme conformations through the action of a strongly bound hydration layer. We further show that DNA nanocages protect encapsulated enzymes against proteases, demonstrating their practical utility in functional biomaterials and biotechnology.

Alcohol Dehydration on Monooxo W=O and Dioxo O=W=O Species

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

Li, Zhenjun; Smid, Bretislav; Kim, Yu Kwon

2012-08-16

The dehydration of 1-propanol on nanoporous WO3 films prepared via ballistic deposition at ~20 K has been investigated using temperature programmed desorption, infrared reflection absorption spectroscopy and density functional theory. The as deposited films are extremely efficient in 1-propanol dehydration to propene. This activity is correlated with the presence of dioxo O=W=O groups while monooxo W=O species are shown to be inactive. Annealing of the film induces densification that results in the loss of catalytic activity due to annihilation O=W=O species.

Layered Double Hydroxide Nanoclusters: Aqueous, Concentrated, Stable, and Catalytically Active Colloids toward Green Chemistry.

PubMed

Tokudome, Yasuaki; Morimoto, Tsuyoshi; Tarutani, Naoki; Vaz, Pedro D; Nunes, Carla D; Prevot, Vanessa; Stenning, Gavin B G; Takahashi, Masahide

2016-05-24

Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which occur in benign aqueous reaction media. Herein, we demonstrate the synthesis of another family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably dispersed (transparent sol for >2 weeks), and catalytically active colloids of nano LDHs (isotropic shape with the size of 7.8 nm as determined by small-angle X-ray scattering). LDH nanoclusters are available as colloidal building blocks to give access to meso- and macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical and chemical features of this colloid, the formation mechanism, and the ability to act as basic nanocatalysts in benign aqueous reaction systems.

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

NASA Astrophysics Data System (ADS)

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

2015-07-01

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

Identification of a Catalytically Highly Active Surface Phase for CO Oxidation over PtRh Nanoparticles under Operando Reaction Conditions

NASA Astrophysics Data System (ADS)

Hejral, U.; Franz, D.; Volkov, S.; Francoual, S.; Strempfer, J.; Stierle, A.

2018-03-01

Pt-Rh alloy nanoparticles on oxide supports are widely employed in heterogeneous catalysis with applications ranging from automotive exhaust control to energy conversion. To improve catalyst performance, an atomic-scale correlation of the nanoparticle surface structure with its catalytic activity under industrially relevant operando conditions is essential. Here, we present x-ray diffraction data sensitive to the nanoparticle surface structure combined with in situ mass spectrometry during near ambient pressure CO oxidation. We identify the formation of ultrathin surface oxides by detecting x-ray diffraction signals from particular nanoparticle facets and correlate their evolution with the sample's enhanced catalytic activity. Our approach opens the door for an in-depth characterization of well-defined, oxide-supported nanoparticle based catalysts under operando conditions with unprecedented atomic-scale resolution.

Extending Thymidine Kinase Activity to the Catalytic Repertoire of Human Deoxycytidine Kinase

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

Hazra, Saugata; Sabini, Eliszbetta; Ort, Stephan

Salvage of nucleosides in the cytosol of human cells is carried out by deoxycytidine kinase (dCK) and thymidine kinase 1 (TK1). Whereas TK1 is only responsible for thymidine phosphorylation, dCK is capable of converting dC, dA, and dG into their monophosphate forms. Using structural data on dCK, we predicted that select mutations at the active site would, in addition to making the enzyme faster, expand the catalytic repertoire of dCK to include thymidine. Specifically, we hypothesized that steric repulsion between the methyl group of the thymine base and Arg104 is the main factor preventing the phosphorylation of thymidine by wild-typemore » dCK. Here we present kinetic data on several dCK variants where Arg104 has been replaced by select residues, all performed in combination with the mutation of Asp133 to an alanine. We show that several hydrophobic residues at position 104 endow dCK with thymidine kinase activity. Depending on the exact nature of the mutations, the enzyme's substrate preference is modified. The R104M-D133A double mutant is a pyrimidine-specific enzyme due to large K{sub m} values with purines. The crystal structure of the double mutant R104M-D133A in complex with the L-form of thymidine supplies a structural explanation for the ability of this variant to phosphorylate thymidine and thymidine analogs. The replacement of Arg104 by a smaller residue allows L-dT to bind deeper into the active site, making space for the C5-methyl group of the thymine base. The unique catalytic properties of several of the mutants make them good candidates for suicide-gene/protein-therapy applications.« less

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.

Few-Layer MoSe2 Possessing High Catalytic Activity towards Iodide/Tri-iodide Redox Shuttles

PubMed Central

Lee, Lawrence Tien Lin; He, Jian; Wang, Baohua; Ma, Yaping; Wong, King Young; Li, Quan; Xiao, Xudong; Chen, Tao

2014-01-01

Due to the two-dimensional confinement of electrons, single- and few-layer MoSe2 nanostructures exhibit unusual optical and electrical properties and have found wide applications in catalytic hydrogen evolution reaction, field effect transistor, electrochemical intercalation, and so on. Here we present a new application in dye-sensitized solar cell as catalyst for the reduction of I3− to I− at the counter electrode. The few-layer MoSe2 is fabricated by surface selenization of Mo-coated soda-lime glass. Our results show that the few-layer MoSe2 displays high catalytic efficiency for the regeneration of I− species, which in turn yields a photovoltaic energy conversion efficiency of 9.00%, while the identical photoanode coupling with “champion” electrode based on Pt nanoparticles on FTO glass generates efficiency only 8.68%. Thus, a Pt- and FTO-free counter electrode outperforming the best conventional combination is obtained. In this electrode, Mo film is found to significantly decrease the sheet resistance of the counter electrode, contributing to the excellent device performance. Since all of the elements in the electrode are of high abundance ratios, this type of electrode is promising for the fabrication of large area devices at low materials cost. PMID:24525919

Effect of ultrasonic treatment of palygorskite on the catalytic performance of Pd-Cu/palygorskite catalyst for room temperature CO oxidation in humid circumstances.

PubMed

Wang, Yongzhao; Wang, Yongning; Li, Xiao; Liu, Zhaotie; Zhao, Yongxiang

2018-03-01

Pd-Cu/palygorskite catalysts were prepared by a wet impregnation method using palygorskite (PC/N-Pal) and ultrasonic-treated palygorskite (PC/U-Pal) as the support. Their catalytic activities toward CO oxidation at room temperature and in humid circumstances were investigated. PC/U-Pal exhibits much higher catalytic activity and stability than PC/N-Pal under the conditions of 1.0 vol.% CO and 3.3 vol.% H 2 O in the feed gas. The X-ray diffraction results indicate that quartz impurities were eliminated from the Pal after the ultrasonic treatment, and more copper species exist in the form of Cu 2 Cl(OH) 3 in PC/U-Pal. The temperature-programmed reduction results suggest that there is an enhanced reducibility of PC/U-Pal after ultrasonic treatment. Furthermore, the ultrasonic treatment can properly decrease the hydrophilicity of the support and catalyst, which may also contribute to the excellent catalytic performance.

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

PubMed

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

2003-06-01

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

Synthesis, characterizations and catalytic studies of a new two-dimensional metal-organic framework based on Co-carboxylate secondary building units

NASA Astrophysics Data System (ADS)

Bagherzadeh, Mojtaba; Ashouri, Fatemeh; Đaković, Marijana

2015-03-01

A metal-organic framework [Co3(BDC)3(DMF)2(H2O)2] was synthesized and structurally characterized. X-ray single crystal analysis revealed that the framework contains a 2D polymeric chain through coordination of 1,4-benzenedicarboxylic acid linker ligand to cobalt centers. The polymer crystallize in monoclinic P21/n space group with a=13.989(3) Å, b=9.6728(17) Å, c=16.707(3) Å, and Z=2. The polymer features a framework based on the perfect octahedral Co-O6 secondary building units. The catalytic activities of [Co3(BDC)3(DMF)2(H2O)2]n for olefins oxidation was conducted. The heterogeneous catalyst could be facilely separated from the reaction mixture, and reused three times without significant degradation in catalytic activity. Furthermore, no contribution from homogeneous catalysis of active species leaching into reaction solution was detected.

Protein-mimicking nanowire-inspired electro-catalytic biosensor for probing acetylcholinesterase activity and its inhibitors.

PubMed

Zhang, Qingqing; Hu, Yufang; Wu, Di; Ma, Shaohua; Wang, Jiao; Rao, Jiajia; Xu, Lihua; Xu, Huan; Shao, Huili; Guo, Zhiyong; Wang, Sui

2018-06-01

A highly sensitive electrochemical biosensor based on the synthetized L-Cysteine-Ag(I) coordination polymer (L-Cys-Ag(I) CP), which looks like a protein-mimicking nanowire, was constructed to detect acetylcholinesterase (AChE) activity and screen its inhibitors. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce hydrogen peroxide (H 2 O 2 ), thus L-Cys-Ag(I) CP possesses the electro-catalytic property to H 2 O 2 reduction. Herein, the protein-mimicking nanowire-based platform was capable of investigating successive of H 2 O 2 effectively by amperometric i-t (current-time) response, and was further applied for the turn-on electrochemical detection of AChE activity. The proposed sensor is highly sensitive (limit of detection is 0.0006 U/L) and is feasible for screening inhibitors of AChE. The model for AChE inhibition was further established and two traditional AChE inhibitors (donepezil and tacrine) were employed to verify the feasibility of the system. The IC 5 0 of donepezil and tacrine were estimated to be 1.4 nM and 3.5 nM, respectively. The developed protocol provides a new and promising platform for probing AChE activity and screening its inhibitors with low cost, high sensitivity and selectivity. Copyright © 2018 Elsevier B.V. All rights reserved.

Correlating the chemical composition and size of various metal oxide substrates with the catalytic activity and stability of as-deposited Pt nanoparticles for the methanol oxidation reaction

DOE PAGES

Megan E. Scofield; Wong, Stanislaus S.; Koenigsmann, Christopher; ...

2015-12-09

The performance of electrode materials in conventional direct alcohol fuel cells (DAFC) is constrained by (i) the low activity of the catalyst materials relative to their overall cost, (ii) the poisoning of the active sites due to the presence of partially oxidized carbon species (such as but not limited to CO, formate, and acetate) produced during small molecule oxidation, and (iii) the lack of catalytic stability and durability on the underlying commercial carbon support. Therefore, as a viable alternative, we have synthesized various metal oxide and perovskite materials of different sizes and chemical compositions as supports for Pt nanoparticles (NPs).more » Our results including unique mechanistic studies demonstrate that the SrRuO 3 substrate with immobilized Pt NPs at its surface evinces the best methanol oxidation performance as compared with all of the other substrate materials tested herein, including commercial carbon itself. In addition, data from electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of electron transfer from bound Pt NPs to surface Ru species within the SrRuO 3 substrate itself, thereby suggesting that favorable metal support interactions are responsible for the increased methanol oxidation reaction (MOR) activity of Pt species with respect to the underlying SrRuO 3 composite catalyst material.« less

Enhancing catalytic activity by narrowing local energy gaps--X-ray studies of a manganese water oxidation catalyst.

PubMed

Xiao, Jie; Khan, Munirah; Singh, Archana; Suljoti, Edlira; Spiccia, Leone; Aziz, Emad F

2015-03-01

Changes in the local electronic structure of the Mn 3d orbitals of a Mn catalyst derived from a dinuclear Mn(III) complex during the water oxidation cycle were investigated ex situ by X-ray absorption spectroscopy (XAS) and resonant inelastic X-ray scattering (RIXS) analyses. Detailed information about the Mn 3d orbitals, especially the local HOMO-LUMO gap on Mn sites revealed by RIXS analyses, indicated that the enhancement in catalytic activity (water oxidation) originated from the narrowing of the local HOMO-LUMO gap when electrical voltage and visible light illumination were applied simultaneously to the Mn catalytic system. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Synthesis, characterizations and catalytic activities of CoFe2O4 nanoparticles

NASA Astrophysics Data System (ADS)

Verma, Divya; Sharma, Vikash; Parmar, Sarita; Okram, Gunadhor Singh; Jain, Shubha

2018-05-01

We report the synthesis of CoFe2O4 nanoparticles (NPs) through a novel one-step coprecipitation method. These NPs were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared (FTIR), and Raman spectroscopy. These nano ferrites were successfully used for the synthesis of 3, 4-dihydropyrimidin-2(1H)-ones and thiones. They can be easily recovered by simple filtration and their catalytic activity remains nearly unaltered even after 4 consecutive cycles, making them ecofriendly and widely applicable due to their efficiency, ease of handling, and cost effectiveness.

Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials

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

Bedford, Nicholas M.; Showalter, Allison R.; Woehl, Taylor J.

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when mixing two different metallic species at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesizedmore » with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods were then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence-dependence in both surface structure and surface composition. Replica exchange solute tempering molecular dynamic simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Finally, taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be

Peptide-Directed PdAu Nanoscale Surface Segregation: Toward Controlled Bimetallic Architecture for Catalytic Materials

DOE PAGES

Bedford, Nicholas M.; Showalter, Allison R.; Woehl, Taylor J.; ...

2016-09-01

Bimetallic nanoparticles are of immense scientific and technological interest given the synergistic properties observed when mixing two different metallic species at the nanoscale. This is particularly prevalent in catalysis, where bimetallic nanoparticles often exhibit improved catalytic activity and durability over their monometallic counterparts. Yet despite intense research efforts, little is understood regarding how to optimize bimetallic surface composition and structure synthetically using rational design principles. Recently, it has been demonstrated that peptide-enabled routes for nanoparticle synthesis result in materials with sequence-dependent catalytic properties, providing an opportunity for rational design through sequence manipulation. In this study, bimetallic PdAu nanoparticles are synthesizedmore » with a small set of peptides containing known Pd and Au binding motifs. The resulting nanoparticles were extensively characterized using high-resolution scanning transmission electron microscopy, X-ray absorption spectroscopy and high-energy X-ray diffraction coupled to atomic pair distribution function analysis. Structural information obtained from synchrotron radiation methods were then used to generate model nanoparticle configurations using reverse Monte Carlo simulations, which illustrate sequence-dependence in both surface structure and surface composition. Replica exchange solute tempering molecular dynamic simulations were also used to predict the modes of peptide binding on monometallic surfaces, indicating that different sequences bind to the metal interfaces via different mechanisms. As a testbed reaction, electrocatalytic methanol oxidation experiments were performed, wherein differences in catalytic activity are clearly observed in materials with identical bimetallic composition. Finally, taken together, this study indicates that peptides could be used to arrive at bimetallic surfaces with enhanced catalytic properties, which could be

N-Methylamino Pyrimidyl Amides (MAPA): Highly Reactive, Electronically-Activated Amides in Catalytic N-C(O) Cleavage.

PubMed

Meng, Guangrong; Lalancette, Roger; Szostak, Roman; Szostak, Michal

2017-09-01

Despite recent progress in catalytic cross-coupling technologies, the direct activation of N-alkyl-N-aryl amides has been a challenging transformation. Here, we report the first Suzuki cross-coupling of N-methylamino pyrimidyl amides (MAPA) enabled by the controlled n N → π Ar conjugation and the resulting remodeling of the partial double bond character of the amide bond. The new mode of amide activation is suitable for generating acyl-metal intermediates from unactivated primary and secondary amides.

Comparison of the catalytic activity for the Suzuki-Miyaura reaction of (η(5)-Cp)Pd(IPr)Cl with (η(3)-cinnamyl)Pd(IPr)(Cl) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl).

PubMed

Melvin, Patrick R; Hazari, Nilay; Lant, Hannah M C; Peczak, Ian L; Shah, Hemali P

2015-01-01

Complexes of the type (η(3)-allyl)Pd(L)(Cl) and (η(3)-indenyl)Pd(L)(Cl) are highly active precatalysts for the Suzuki-Miyaura reaction. Even though allyl and indenyl ligands are similar to cyclopentadienyl (Cp) ligands, there have been no detailed comparative studies exploring the activity of precatalysts of the type (η(5)-Cp)Pd(L)(Cl) for Suzuki-Miyaura reactions. Here, we compare the catalytic activity of (η(5)-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η(3)-cinnamyl)Pd(IPr)(Cl) (Cin) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl) ( (tBu) Ind). We show that Cp gives slightly better catalytic activity than Cin, but significantly inferior activity than (tBu) Ind. This order of activity is rationalized by comparing the rates at which the precatalysts are activated to the monoligated Pd(0) active species along with the tendency of the starting precatalysts to comproportionate with monoligated Pd(0) to form inactive Pd(I) dimers. As part of this work the Cp supported Pd(I) dimer (μ-Cp)(μ-Cl)Pd2(IPr)2 (Cp (Dim) ) was synthesized and crystallographically characterized. It does not readily disproportionate to form monoligated Pd(0) and consequently Cp (Dim) is a poor catalyst for the Suzuki-Miyaura reaction.

Comparison of the catalytic activity for the Suzuki–Miyaura reaction of (η5-Cp)Pd(IPr)Cl with (η3-cinnamyl)Pd(IPr)(Cl) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl)

PubMed Central

Melvin, Patrick R; Lant, Hannah M C; Peczak, Ian L; Shah, Hemali P

2015-01-01

Summary Complexes of the type (η3-allyl)Pd(L)(Cl) and (η3-indenyl)Pd(L)(Cl) are highly active precatalysts for the Suzuki–Miyaura reaction. Even though allyl and indenyl ligands are similar to cyclopentadienyl (Cp) ligands, there have been no detailed comparative studies exploring the activity of precatalysts of the type (η5-Cp)Pd(L)(Cl) for Suzuki–Miyaura reactions. Here, we compare the catalytic activity of (η5-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η3-cinnamyl)Pd(IPr)(Cl) (Cin) and (η3-1-t-Bu-indenyl)Pd(IPr)(Cl) (tBu Ind). We show that Cp gives slightly better catalytic activity than Cin, but significantly inferior activity than tBu Ind. This order of activity is rationalized by comparing the rates at which the precatalysts are activated to the monoligated Pd(0) active species along with the tendency of the starting precatalysts to comproportionate with monoligated Pd(0) to form inactive Pd(I) dimers. As part of this work the Cp supported Pd(I) dimer (μ-Cp)(μ-Cl)Pd2(IPr)2 (Cp Dim) was synthesized and crystallographically characterized. It does not readily disproportionate to form monoligated Pd(0) and consequently Cp Dim is a poor catalyst for the Suzuki–Miyaura reaction. PMID:26732227

Probing Substrate Interactions in the Active Tunnel of a Catalytically Deficient Cellobiohydrolase (Cel7)*

PubMed Central

Colussi, Francieli; Sørensen, Trine H.; Alasepp, Kadri; Kari, Jeppe; Cruys-Bagger, Nicolaj; Windahl, Michael S.; Olsen, Johan P.; Borch, Kim; Westh, Peter

2015-01-01

Cellobiohydrolases break down cellulose sequentially by sliding along the crystal surface with a single cellulose strand threaded through the catalytic tunnel of the enzyme. This so-called processive mechanism relies on a complex pattern of enzyme-substrate interactions, which need to be addressed in molecular descriptions of processivity and its driving forces. Here, we have used titration calorimetry to study interactions of cellooligosaccharides (COS) and a catalytically deficient variant (E212Q) of the enzyme Cel7A from Trichoderma reesei. This enzyme has ∼10 glucopyranose subsites in the catalytic tunnel, and using COS ligands with a degree of polymerization (DP) from 2 to 8, different regions of the tunnel could be probed. For COS ligands with a DP of 2–3 the binding constants were around 105 m−1, and for longer ligands (DP 5–8) this value was ∼107 m−1. Within each of these groups we did not find increased affinity as the ligands got longer and potentially filled more subsites. On the contrary, we found a small but consistent affinity loss as DP rose from 6 to 8, particularly at the higher investigated temperatures. Other thermodynamic functions (ΔH, ΔS, and ΔCp) decreased monotonously with both temperature and DP. Combined interpretation of these thermodynamic results and previously published structural data allowed assessment of an affinity profile along the length axis of the active tunnel. PMID:25477511

Catalytic activity of Ru-Sn/Al2O3 in reduction reaction of pollutant 4-Nitrophenol

NASA Astrophysics Data System (ADS)

Rini, A. S.; Radiman, S.; Yarmo, M. A.

2018-03-01

Ru-Sn/Al2O3 bimetallic nanocatalysts have been synthesized by using conventional and microwave impregnation methods. Structure and morphology of the samples were characterized using XRD, XPS, and TEM. XRD and XPS measurement have confirmed the presence of Ru and Sn in the samples. According to TEM results, the morphology of the catalyst strongly depends on the preparation route and stabilizing agent (i.e. PVP). The sample with PVP (polyvinylpyrrolidone) has better nanoparticles distribution over the support. A sample prepared by conventional method has an agglomeration of nanoparticles on the support. Catalytic activities of both samples were examined in the reduction reaction of pollutant, i.e. 4-nitrophenol. Catalytic examination showed that reaction rate of 4-nitrophenol reduction by using microwave-assisted sample has improved 3.5 times faster than conventional impregnation sample.

Catalytic ignition model in a monolithic reactor with in-depth reaction

NASA Technical Reports Server (NTRS)

Tien, Ta-Ching; Tien, James S.

1990-01-01

Two transient models have been developed to study the catalytic ignition in a monolithic catalytic reactor. The special feature in these models is the inclusion of thermal and species structures in the porous catalytic layer. There are many time scales involved in the catalytic ignition problem, and these two models are developed with different time scales. In the full transient model, the equations are non-dimensionalized by the shortest time scale (mass diffusion across the catalytic layer). It is therefore accurate but is computationally costly. In the energy-integral model, only the slowest process (solid heat-up) is taken as nonsteady. It is approximate but computationally efficient. In the computations performed, the catalyst is platinum and the reactants are rich mixtures of hydrogen and oxygen. One-step global chemical reaction rates are used for both gas-phase homogeneous reaction and catalytic heterogeneous reaction. The computed results reveal the transient ignition processes in detail, including the structure variation with time in the reactive catalytic layer. An ignition map using reactor length and catalyst loading is constructed. The comparison of computed results between the two transient models verifies the applicability of the energy-integral model when the time is greater than the second largest time scale of the system. It also suggests that a proper combined use of the two models can catch all the transient phenomena while minimizing the computational cost.

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

Two stage catalytic combustor

NASA Technical Reports Server (NTRS)

Alvin, Mary Anne (Inventor); Bachovchin, Dennis (Inventor); Smeltzer, Eugene E. (Inventor); Lippert, Thomas E. (Inventor); Bruck, Gerald J. (Inventor)

2010-01-01

A catalytic combustor (14) includes a first catalytic stage (30), a second catalytic stage (40), and an oxidation completion stage (49). The first catalytic stage receives an oxidizer (e.g., 20) and a fuel (26) and discharges a partially oxidized fuel/oxidizer mixture (36). The second catalytic stage receives the partially oxidized fuel/oxidizer mixture and further oxidizes the mixture. The second catalytic stage may include a passageway (47) for conducting a bypass portion (46) of the mixture past a catalyst (e.g., 41) disposed therein. The second catalytic stage may have an outlet temperature elevated sufficiently to complete oxidation of the mixture without using a separate ignition source. The oxidation completion stage is disposed downstream of the second catalytic stage and may recombine the bypass portion with a catalyst exposed portion (48) of the mixture and complete oxidation of the mixture. The second catalytic stage may also include a reticulated foam support (50), a honeycomb support, a tube support or a plate support.

Fluorine-doped carbon nanotubes as an efficient metal-free catalyst for destruction of organic pollutants in catalytic ozonation.

PubMed

Wang, Jing; Chen, Shuo; Quan, Xie; Yu, Hongtao

2018-01-01

Metal-free carbon materials have been presented to be potential alternatives to metal-based catalysts for heterogeneous catalytic ozonation, yet the catalytic performance still needs to be enhanced. Doping carbon with non-metallic heteroatoms (e.g., N, B, and F) could alter the electronic structure and electrochemical properties of original carbon materials, has been considered to be an effective method for improving the catalytic activity of carbon materials. Herein, fluorine-doped carbon nanotubes (F-CNTs) were synthesized via a facile method and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The as-synthesized F-CNTs exhibited notably enhanced catalytic activity towards catalytic ozonation for the degradation of organic pollutants. The oxalic acid removal efficiency of optimized F-CNTs was approximately two times as much as that of pristine CNTs, and even exceeded those of four conventional metal-based catalysts (ZnO, Al 2 O 3 , Fe 2 O 3 , and MnO 2 ). The XPS and Raman studies confirmed that the covalent CF bonds were formed at the sp 3 C sites instead of sp 2 C sites on CNTs, not only resulting in high positive charge density of C atoms adjacent to F atoms, but remaining the delocalized π-system with intact carbon structure of F-CNTs, which then favored the conversion of ozone molecules (O 3 ) into reactive oxygen species (ROS) and contributed to the high oxalic acid removal efficiency. Furthermore, electron spin resonance (ESR) studies revealed that superoxide radicals (O 2 - ) and singlet oxygen ( 1 O 2 ) might be the dominant ROS that responsible for the degradation of oxalic acid in these catalytic systems. Copyright © 2017 Elsevier Ltd. All rights reserved.

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

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

Li, Shujun; Peng, Qingpo; Chen, Xuenian, E-mail: xnchen@htu.edu.cn

A new HPAs H{sub 20}[P{sub 8}W{sub 60}Ta{sub 12}(H{sub 2}O){sub 4}(OH){sub 8}O{sub 236}]·125H{sub 2}O (H-1) which comprises a Ta/W mixed addenda heteropolyanion, 20 protons, and 125 crystalline water molecules has been prepared through ion-exchange method. The structure and properties of H-1 have been explored in detail. AC impedance measurements indicate that H-1 is a good solid state proton conducting material at room temperature with a conductivity value of 7.2×10{sup −3} S cm{sup −1} (25 °C, 30% RH). Cyclic voltammograms of H-1 indicate the electrocatalytic activity towards the reduction of nitrite. Hammett acidity constant H{sub 0} of H-1 in CH{sub 3}CN ismore » −2.91, which is the strongest among the present known HPAs. Relatively, H-1 exhibits excellent catalytic activities toward acetal reaction. - Highlights: • A Ta/W mixed addenda Heteropolyacid (H-1) was isolated. • Hammett acidity constant H{sub 0} of H-1 is the strongest among the present known HPAs. • H-1 exhibits excellent catalytic activities toward acetal reaction. • H-1 is a good solid state proton conducting material at room temperature.« 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.

WD40 domain of Apc1 is critical for the coactivator-induced allosteric transition that stimulates APC/C catalytic activity.

PubMed

Li, Qiuhong; Chang, Leifu; Aibara, Shintaro; Yang, Jing; Zhang, Ziguo; Barford, David

2016-09-20

The anaphase-promoting complex/cyclosome (APC/C) is a large multimeric cullin-RING E3 ubiquitin ligase that orchestrates cell-cycle progression by targeting cell-cycle regulatory proteins for destruction via the ubiquitin proteasome system. The APC/C assembly comprises two scaffolding subcomplexes: the platform and the TPR lobe that together coordinate the juxtaposition of the catalytic and substrate-recognition modules. The platform comprises APC/C subunits Apc1, Apc4, Apc5, and Apc15. Although the role of Apc1 as an APC/C scaffolding subunit has been characterized, its specific functions in contributing toward APC/C catalytic activity are not fully understood. Here, we report the crystal structure of the N-terminal domain of human Apc1 (Apc1N) determined at 2.2-Å resolution and provide an atomic-resolution description of the architecture of its WD40 (WD40 repeat) domain (Apc1(WD40)). To understand how Apc1(WD40) contributes to APC/C activity, a mutant form of the APC/C with Apc1(WD40) deleted was generated and evaluated biochemically and structurally. We found that the deletion of Apc1(WD40) abolished the UbcH10-dependent ubiquitination of APC/C substrates without impairing the Ube2S-dependent ubiquitin chain elongation activity. A cryo-EM structure of an APC/C-Cdh1 complex with Apc1(WD40) deleted showed that the mutant APC/C is locked into an inactive conformation in which the UbcH10-binding site of the catalytic module is inaccessible. Additionally, an EM density for Apc15 is not visible. Our data show that Apc1(WD40) is required to mediate the coactivator-induced conformational change of the APC/C that is responsible for stimulating APC/C catalytic activity by promoting UbcH10 binding. In contrast, Ube2S activity toward APC/C substrates is not dependent on the initiation-competent conformation of the APC/C.

WD40 domain of Apc1 is critical for the coactivator-induced allosteric transition that stimulates APC/C catalytic activity

PubMed Central

Li, Qiuhong; Chang, Leifu; Aibara, Shintaro; Yang, Jing; Zhang, Ziguo; Barford, David

2016-01-01

The anaphase-promoting complex/cyclosome (APC/C) is a large multimeric cullin–RING E3 ubiquitin ligase that orchestrates cell-cycle progression by targeting cell-cycle regulatory proteins for destruction via the ubiquitin proteasome system. The APC/C assembly comprises two scaffolding subcomplexes: the platform and the TPR lobe that together coordinate the juxtaposition of the catalytic and substrate-recognition modules. The platform comprises APC/C subunits Apc1, Apc4, Apc5, and Apc15. Although the role of Apc1 as an APC/C scaffolding subunit has been characterized, its specific functions in contributing toward APC/C catalytic activity are not fully understood. Here, we report the crystal structure of the N-terminal domain of human Apc1 (Apc1N) determined at 2.2-Å resolution and provide an atomic-resolution description of the architecture of its WD40 (WD40 repeat) domain (Apc1WD40). To understand how Apc1WD40 contributes to APC/C activity, a mutant form of the APC/C with Apc1WD40 deleted was generated and evaluated biochemically and structurally. We found that the deletion of Apc1WD40 abolished the UbcH10-dependent ubiquitination of APC/C substrates without impairing the Ube2S-dependent ubiquitin chain elongation activity. A cryo-EM structure of an APC/C–Cdh1 complex with Apc1WD40 deleted showed that the mutant APC/C is locked into an inactive conformation in which the UbcH10-binding site of the catalytic module is inaccessible. Additionally, an EM density for Apc15 is not visible. Our data show that Apc1WD40 is required to mediate the coactivator-induced conformational change of the APC/C that is responsible for stimulating APC/C catalytic activity by promoting UbcH10 binding. In contrast, Ube2S activity toward APC/C substrates is not dependent on the initiation-competent conformation of the APC/C. PMID:27601667

Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

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

Getsoian, Andrew G. Bean; Hu, Bo; Miller, Jeffrey T.

Single site Sc and Y on silica catalysts have been prepared by aqueous and organometallic grafting methods. The former yields Y(III) ions with 5 bonds at an average bond distance of 2.31 Å by X-ray absorption spectroscopy. Although the aqueous synthesis gave single site Y with low coordination number, these were not catalytic for alkane dehydrogenation or olefin hydrogenation. Single site Sc(III) and Y(III) species were also prepared by grafting Sc(CH 2Si(CH 3) 3) 3(THF) 2 and Y(CH 2Si(CH 3) 3) 3(THF) 2, respectively and these are catalysts for olefin hydrogenation at temperatures from about 60 to 100°C; however, theymore » were thermally unstable at higher temperatures necessary for alkane dehydrogenation. The structure of the grafted Y complex was determined by X-ray absorption spectroscopy, IR, and NMR. Grafting lead to protonolysis of 2 of the 3 CH 2Si(CH 3) 3 ligands. Additionally, there was loss of one THF ligand. The EXAFS indicated that there were 4 Y-ligand bonds in the surface species, 2 at 2.16 Å and 2 at 2.39 Å. The metal-alkyl ligand was thought to be necessary for catalytic activity and likely proceeds through a sigma bond metathesis mechanism. In the single site centers without alkyl bonds, Sc and Y ions cannot generate metal-alkyl, or metal-hydride, moieties in situ. We conclude that this is likely due to the very high M-O-Si bond strengths, which must be broken through heterolytic dissociation of C-H bonds during alkane activation for either alkane dehydrogenation or olefin hydrogenation reactions. Lastly, this study demonstrates the importance of pre-catalyst choice versus in situ formation of reactive intermediates to produce active catalysts for alkane bond activation.« less

Silica-Supported, Single-Site Sc and Y Alkyls for Catalytic Hydrogenation of Propylene

DOE PAGES

Getsoian, Andrew G. Bean; Hu, Bo; Miller, Jeffrey T.; ...

2017-09-27

Single site Sc and Y on silica catalysts have been prepared by aqueous and organometallic grafting methods. The former yields Y(III) ions with 5 bonds at an average bond distance of 2.31 Å by X-ray absorption spectroscopy. Although the aqueous synthesis gave single site Y with low coordination number, these were not catalytic for alkane dehydrogenation or olefin hydrogenation. Single site Sc(III) and Y(III) species were also prepared by grafting Sc(CH 2Si(CH 3) 3) 3(THF) 2 and Y(CH 2Si(CH 3) 3) 3(THF) 2, respectively and these are catalysts for olefin hydrogenation at temperatures from about 60 to 100°C; however, theymore » were thermally unstable at higher temperatures necessary for alkane dehydrogenation. The structure of the grafted Y complex was determined by X-ray absorption spectroscopy, IR, and NMR. Grafting lead to protonolysis of 2 of the 3 CH 2Si(CH 3) 3 ligands. Additionally, there was loss of one THF ligand. The EXAFS indicated that there were 4 Y-ligand bonds in the surface species, 2 at 2.16 Å and 2 at 2.39 Å. The metal-alkyl ligand was thought to be necessary for catalytic activity and likely proceeds through a sigma bond metathesis mechanism. In the single site centers without alkyl bonds, Sc and Y ions cannot generate metal-alkyl, or metal-hydride, moieties in situ. We conclude that this is likely due to the very high M-O-Si bond strengths, which must be broken through heterolytic dissociation of C-H bonds during alkane activation for either alkane dehydrogenation or olefin hydrogenation reactions. Lastly, this study demonstrates the importance of pre-catalyst choice versus in situ formation of reactive intermediates to produce active catalysts for alkane bond activation.« less

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.

Microbial Biofilm Voltammetry: Direct Electrochemical Characterization of Catalytic Electrode-Attached Biofilms▿ †

PubMed Central

Marsili, Enrico; Rollefson, Janet B.; Baron, Daniel B.; Hozalski, Raymond M.; Bond, Daniel R.

2008-01-01

While electrochemical characterization of enzymes immobilized on electrodes has become common, there is still a need for reliable quantitative methods for study of electron transfer between living cells and conductive surfaces. This work describes growth of thin (<20 μm) Geobacter sulfurreducens biofilms on polished glassy carbon electrodes, using stirred three-electrode anaerobic bioreactors controlled by potentiostats and nondestructive voltammetry techniques for characterization of viable biofilms. Routine in vivo analysis of electron transfer between bacterial cells and electrodes was performed, providing insight into the main redox-active species participating in electron transfer to electrodes. At low scan rates, cyclic voltammetry revealed catalytic electron transfer between cells and the electrode, similar to what has been observed for pure enzymes attached to electrodes under continuous turnover conditions. Differential pulse voltammetry and electrochemical impedance spectroscopy also revealed features that were consistent with electron transfer being mediated by an adsorbed catalyst. Multiple redox-active species were detected, revealing complexity at the outer surfaces of this bacterium. These techniques provide the basis for cataloging quantifiable, defined electron transfer phenotypes as a function of potential, electrode material, growth phase, and culture conditions and provide a framework for comparisons with other species or communities. PMID:18849456

CROSS-DISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY: Kinetics of catalytically activated duplication in aggregation growth

NASA Astrophysics Data System (ADS)

Wang, Hai-Feng; Lin, Zhen-Quan; Gao, Yan; Xu, Chao

2009-08-01

We propose a catalytically activated duplication model to mimic the coagulation and duplication of the DNA polymer system under the catalysis of the primer RNA. In the model, two aggregates of the same species can coagulate themselves and a DNA aggregate of any size can yield a new monomer or double itself with the help of RNA aggregates. By employing the mean-field rate equation approach we analytically investigate the evolution behaviour of the system. For the system with catalysis-driven monomer duplications, the aggregate size distribution of DNA polymers ak(t) always follows a power law in size in the long-time limit, and it decreases with time or approaches a time-independent steady-state form in the case of the duplication rate independent of the size of the mother aggregates, while it increases with time increasing in the case of the duplication rate proportional to the size of the mother aggregates. For the system with complete catalysis-driven duplications, the aggregate size distribution ak(t) approaches a generalized or modified scaling form.

Solvothermal synthesis of N-doped graphene supported PtCo nanodendrites with highly catalytic activity for 4-nitrophenol reduction

NASA Astrophysics Data System (ADS)

Zhang, Xiao-Fang; Zhu, Xiao-Yan; Feng, Jiu-Ju; Wang, Ai-Jun

2018-01-01

A simple solvothermal method was developed to prepare N-doped reduced graphene oxide supported homogeneous PtCo nanodendrites (PtCo NDs/N-rGO), where ethylene glycol (EG) served as the reducing agent and the solvent, and linagliptin as the structure-directing and stabilizing agent for PtCo NDs and dopant for rGO, respectively. Controlled researches showed that the dosage of linagliptin and the ratios of the two metal precursors were important in the current synthesis. The PtCo NDs/N-rGO nanocomposite exhibited higher catalytic activity towards the reduction of 4-nitrophnol (4-NP) in contrast with the referenced Pt1Co3 NCs/N-rGO, Pt3Co1 NCs/N-rGO and commercial Pt/C catalysts. More importantly, the constructed catalyst exhibited the superior stability without sacrificing the catalytic activity, showing great prospect for the reduction of 4-NP in practice.

Peroxidase-like catalytic activity of Mn(3+)-octabromo-tetrakis(4-sulfophenyl)porphine on linoleate hydroperoxide and its analytical application.

PubMed

Mifune, Masaki; Kamiguchi, Hidenori; Tai, Taka-Aki; Kuremoto, Seigo; Yamamoto, Makiko; Tsukamoto, Ikuko; Saito, Madoka; Kitamura, Youji; Saito, Yutaka

2007-01-15

To reveal an enzyme-like catalytic activity of metal-octabromo-tetrakis(sulfophenyl)porphines (M-OBPSs), their peroxidease-like catalytic activity on linoleate hydroperoxide (LOOH) were evaluated on the basis of dye-formation in the coloring reaction between N,N-diethylaniline and 4-aminoantipyrine that yields a quinoid-type dye. Among M-OBPSs tested, Mn(3+)-OBPS allowed to produce the largest amount of dye. The optimal conditions of the coloring reaction catalyzed by Mn(3+)-OBPS for the determination of LOOH were determined. A good linear calibration curve was obtained in the concentration range of 0.025-0.4mumole LOOH with good reproducibility (coefficient of variance=1.23%), suggesting that Mn(3+)-OBPS is a good artificial mimesis of the peroxidase for LOOH. In addition, Mn(3+)-OBPS was highly specific for LOOH even in the presence of cumene hydroxyperoxide or hydrogen peroxide. It was revealed that the peroxidase-like activity of Mn(3+)-OBTP is attributable to the redox cycle of Mn(3+)<-->Mn(4+).

Pulsed laser synthesis in liquid of efficient visible-light-active ZnO/rGO nanocomposites for improved photo-catalytic activity

NASA Astrophysics Data System (ADS)

Moqbel, Redhwan A.; Gondal, Mohammed A.; Qahtan, Talal F.; Dastageer, Mohamed A.

2018-03-01

In this work the synthesis of visible light active zinc oxide/reduced graphene oxide (ZnO/rGO) nanocomposite by laser induced fragmentation of particulates in liquid, its morphological/optical characterizations, and its application in the process of photo-catalytic degradation of toxic Rhodamine B (RhB) dye under visible radiation were studied. It is observed from the optical and morphological characterization that the anchoring of ZnO on the rGO sheets in ZnO/rGO nanocomposite considerably reduced the aggregation of ZnO (increased surface area), reduced the recombination of photo-induced charge carriers, promoted more adsorption of reactants on the catalytic surface and also enhanced and extended the light absorption in the visible spectral region. With all these improved characteristics of ZnO/rGO nanocomposite, it was found that this material as a photo-catalyst yielded an RhB degradation efficiency of 86%, as compared to the 40% degradation with pure ZnO NPs under the same experimental conditions. In the ZnO/rGO nanocomposite, rGO functions as an electron acceptor to promote charge separation, an aggregation inhibitor to enhance the active surface area, a co-catalyst, a good dye adsorber and also as a supporting matrix for ZnO.

Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene

PubMed Central

Maldonado, Carolina Solis; De la Rosa, Javier Rivera; Lucio-Ortiz, Carlos J.; Hernández-Ramírez, Aracely; Castillón Barraza, Felipe F.; Valente, Jaime S.

2014-01-01

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al2O3 phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al2O3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al2O3 lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%. PMID:28788556

Low Concentration Fe-Doped Alumina Catalysts Using Sol-Gel and Impregnation Methods: The Synthesis, Characterization and Catalytic Performance during the Combustion of Trichloroethylene.

PubMed

Maldonado, Carolina Solis; De la Rosa, Javier Rivera; Lucio-Ortiz, Carlos J; Hernández-Ramírez, Aracely; Barraza, Felipe F Castillón; Valente, Jaime S

2014-03-12

The role of iron in two modes of integration into alumina catalysts was studied at 0.39 wt% Fe and tested in trichloroethylene combustion. One modified alumina was synthesized using the sol-gel method with Fe added in situ during hydrolysis; another modification was performed using calcined alumina, prepared using the sol-gel method and impregnated with Fe. Several characterization techniques were used to study the level of Fe modification in the γ-Al₂O₃ phase formed and to correlate the catalytic properties during trichloroethylene (TCE) combustion. The introduction of Fe in situ during the sol-gel process influenced the crystallite size, and three iron species were generated, namely, magnetite, maghemite and hematite. The impregnated Fe-alumina formed hematite and maghemite, which were highly dispersed on the γ-Al₂O 3 surface. The X-ray photoelectron spectra (XPS), FT-IR and Mössbauer spectroscopy analyses revealed how Fe interacted with the γ-Al₂O₃ lattice in both catalysts. The impregnated Fe-catalyst showed the best catalytic performance compared to the catalyst that was Fe-doped in situ by the sol-gel method; both had better catalytic activity than pure alumina. This difference in activity was correlated with the accessibility of the reactants to the hematite iron species on the surface. The chlorine poisoning for all three catalysts was less than 1.8%.

High-resolution physical and functional mapping of the template adjacent DNA binding site in catalytically active telomerase.

PubMed

Romi, Erez; Baran, Nava; Gantman, Marina; Shmoish, Michael; Min, Bosun; Collins, Kathleen; Manor, Haim

2007-05-22

Telomerase is a cellular reverse transcriptase, which utilizes an integral RNA template to extend single-stranded telomeric DNA. We used site-specific photocrosslinking to map interactions between DNA primers and the catalytic protein subunit (tTERT) of Tetrahymena thermophila telomerase in functional enzyme complexes. Our assays reveal contact of the single-stranded DNA adjacent to the primer-template hybrid and tTERT residue W187 at the periphery of the N-terminal domain. This contact was detected in complexes with three different registers of template in the active site, suggesting that it is maintained throughout synthesis of a complete telomeric repeat. Substitution of nearby residue Q168, but not W187, alters the K(m) for primer elongation, implying that it plays a role in the DNA recognition. These findings are the first to directly demonstrate the physical location of TERT-DNA contacts in catalytically active telomerase and to identify amino acid determinants of DNA binding affinity. Our data also suggest a movement of the TERT active site relative to the template-adjacent single-stranded DNA binding site within a cycle of repeat synthesis.

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

Correlation between the extent of catalytic activity and charge density of montmorillonites.

PubMed

Ertem, Gözen; Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

2010-09-01

The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH₃-(CH₂)(n)-NH₃](+), where n = 3-16 and 18, and then measuring d(₀₀₁), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed.

Directed evolution of a β-mannanase from Rhizomucor miehei to improve catalytic activity in acidic and thermophilic conditions.

PubMed

Li, Yan-Xiao; Yi, Ping; Yan, Qiao-Juan; Qin, Zhen; Liu, Xue-Qiang; Jiang, Zheng-Qiang

2017-01-01

β-Mannanase randomly cleaves the β-1,4-linked mannan backbone of hemicellulose, which plays the most important role in the enzymatic degradation of mannan. Although the industrial applications of β-mannanase have tremendously expanded in recent years, the wild-type β-mannanases are still defective for some industries. The glycoside hydrolase (GH) family 5 β-mannanase ( Rm Man5A) from Rhizomucor miehei shows many outstanding properties, such as high specific activity and hydrolysis property. However, owing to the low catalytic activity in acidic and thermophilic conditions, the application of Rm Man5A to the biorefinery of mannan biomasses is severely limited. To overcome the limitation, Rm Man5A was successfully engineered by directed evolution. Through two rounds of screening, a mutated β-mannanase (m Rm Man5A) with high catalytic activity in acidic and thermophilic conditions was obtained, and then characterized. The mutant displayed maximal activity at pH 4.5 and 65 °C, corresponding to acidic shift of 2.5 units in optimal pH and increase by 10 °C in optimal temperature. The catalytic efficiencies ( k cat / K m ) of m Rm Man5A towards many mannan substrates were enhanced more than threefold in acidic and thermophilic conditions. Meanwhile, the high specific activity and excellent hydrolysis property of Rm Man5A were inherited by the mutant m Rm Man5A after directed evolution. According to the result of sequence analysis, three amino acid residues were substituted in m Rm Man5A, namely Tyr233His, Lys264Met, and Asn343Ser. To identify the function of each substitution, four site-directed mutations (Tyr233His, Lys264Met, Asn343Ser, and Tyr233His/Lys264Met) were subsequently generated, and the substitutions at Tyr233 and Lys264 were found to be the main reason for the changes of m Rm Man5A. Through directed evolution of Rm Man5A, two key amino acid residues that controlled its catalytic efficiency under acidic and thermophilic conditions were identified

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

Raney nickel catalytic device

DOEpatents

O'Hare, Stephen A.

1978-01-01

A catalytic device for use in a conventional coal gasification process which includes a tubular substrate having secured to its inside surface by expansion a catalytic material. The catalytic device is made by inserting a tubular catalytic element, such as a tubular element of a nickel-aluminum alloy, into a tubular substrate and heat-treating the resulting composite to cause the tubular catalytic element to irreversibly expand against the inside surface of the substrate.

Catalytic methods using molecular oxygen for treatment of PMMS and ECLSS waste streams, volume 2

NASA Technical Reports Server (NTRS)

Akse, James R.

1992-01-01

Catalytic oxidation has proven to be an effective addition to the baseline sorption, ion exchange water reclamation technology which will be used on Space Station Freedom (SSF). Low molecular weight, polar organics such as alcohols, aldehydes, ketones, amides, and thiocarbamides which are poorly removed by the baseline multifiltration (MF) technology can be oxidized to carbon dioxide at low temperature (121 C). The catalytic oxidation process by itself can reduce the Total Organic Carbon (TOC) to below 500 ppb for solutions designed to model these waste waters. Individual challenges by selected contaminants have shown only moderate selectivity towards particular organic species. The combined technology is applicable to the more complex waste water generated in the Process Materials Management System (PMMS) and Environmental Control and Life Support System (ECLSS) aboard SSF. During the phase 3 Core Module Integrated Facility (CMIF) water recovery tests at NASA MSFC, real hygiene waste water and humidity condensate were processed to meet potable specifications by the combined technology. A kinetic study of catalytic oxidation demonstrates that the Langmuir-Hinshelwood rate equation for heterogeneous catalysts accurately represent the kinetic behavior. From this relationship, activation energy and rate constants for acetone were determined.

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

PubMed

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

2014-09-01

The current study describes an approach to creation of catalytically active particles with increased stability from enzymes by N-homocysteinylation, a naturally presented protein modification. Enzymatic activities and properties of two globular tetrameric enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase (LDH) were studied before and after N-homocysteinylation. Modification of these proteins concerns the accessible lysine residues and introduces an average of 2-2,5 homocysteine residues per protein monomer. Formation of a range of aggregates was observed for both enzymes, which assemble via formation of intermolecular noncovalent bonds and by disulfide bonds. It was demonstrated that both studied enzymes retain their catalytic activities on modification and the subsequent formation of oligomeric forms. At low concentrations of homocysteine thiolactone, modification of GAPDH leads not only to prevention of spontaneous inactivation but also increases thermal stability of this enzyme on heating to 80°C. A moderate reduction of the activity of GAPDH observed in case of its crosslinking with 50-fold excess of homocysteine thiolactone per lysine is probably caused by hindered substrate diffusion. Spherical particles of 100 nm and larger diameters were observed by transmission electron microscopy and atomic force microscope techniques after modification of GAPDH with different homocysteine thiolactone concentrations. In case of LDH, branched fibril-like aggregates were observed under the same conditions. Interestingly, crosslinked samples of both proteins were found to have reversible thermal denaturation profiles, indicating that modification with homocysteine thiolactone stabilizes the spatial structure of these enzymes. © 2014 Wiley Periodicals, Inc.

Boosting the catalytic activity of natural magnetite for wet peroxide oxidation.

PubMed

Álvarez-Torrellas, Silvia; Munoz, Macarena; Mondejar, Victor; de Pedro, Zahara M; Casas, Jose A

2018-06-02

This work explores the modification of naturally occurring magnetite by controlled oxidation (200-400 °C, air atmosphere) and reduction (300-600 °C, H 2 atmosphere) treatments with the aim of boosting its activity in CWPO. The resulting materials were fully characterized by XRD, XPS, TGA, TPR, SEM, and magnetization measurements, allowing to confirm the development of core-shell type structures. The magnetite core of the solid remained unchanged upon the treatment whereas the Fe(II)/Fe(III) ratio of the shell was modified (e.g. 0.42, 0.11 and 0.63 values were calculated for pristine Fe 3 O 4 , Fe 3 O 4 -O400, and Fe 3 O 4 -R400, respectively). The performance of the catalysts was tested in the CWPO of sulfamethoxazole (SMX) (5 mg L -1 ) under ambient conditions and circumneutral pH (pH 0  = 5), using the stoichiometric dose of H 2 O 2 (25 mg L -1 ) and a catalyst load of 1 g L -1 . The key role of the ferrous species on the mineral shell was evidenced. Whereas the oxidation of magnetite led to significantly slower degradation rates of the pollutant, its reduction gave rise to a dramatic increase, achieving the complete removal of SMX in 1.5 h reaction time with the optimum catalyst (Fe 3 O 4 -R400) compared to the 3.5 h required with the pristine mineral. A reaction mechanism was proposed for SMX degradation, and a kinetic equation based on the Eley-Rideal model was accordingly developed. This model successfully fitted the experimental results. The stability of Fe 3 O 4 -R400 was evaluated upon five sequential runs. Finally, the versatility of the catalytic system was proved in real environmentally relevant water matrices.

Green Synthesis of Silver Nanoparticles Decorated by Fe₃O₄/GO with Enhanced Catalytic Activity.

PubMed

Guo, Jian; Wang, Yu; Liu, Dan-Dan; Wan, Rong; Han, Guo-Zhi

2018-05-01

We report a simple and green approach to synthesize stable water-dispersible silver nanoparticles decorated by magnetic Fe3O4 and graphene oxide (GO). These results of UV-Vis spectra, along with TEM and SEM indicated that the water-dispersible silver nanoparticles had cluster flat structure and retained the optical properties of the original silver particle. Combining the advantages of Fe3O4 and GO, the composite nanoparticles showed enhanced catalytic activity with good recycling utilization rate by magnetic separation.

Synthesis, spectral characterization and catalytic activity of Co(II) complexes of drugs: crystal structure of Co(II)-trimethoprim complex.

PubMed

Madhupriya, Selvaraj; Elango, Kuppanagounder P

2014-01-24

New Co(II) complexes with drugs such as trimethoprim (TMP), cimetidine (CTD), niacinamide (NAM) and ofloxacin (OFL) as ligands were synthesized. The complexes were characterized by analytical analysis, various spectral techniques such as FT-IR, UV-Vis, magnetic measurements and molar conductivity. The magnetic susceptibility results coupled with the electronic spectra suggested a tetrahedral geometry for the complexes. The coordination mode of trimethoprim ligand and geometry of the complex were confirmed by single crystal X-ray studies. In this complex the metal ion possesses a tetrahedral geometry with two nitrogen atom from two TMP ligands and two chloride ions coordinated to it. The catalytic activity of the complexes in aryl-aryl coupling reaction was screened and the results indicated that among the four complexes [Co(OFL)Cl(H2O)] exhibited excellent catalytic activity. Copyright © 2013 Elsevier B.V. All rights reserved.

Catalytic, Enantioselective Sulfenofunctionalisation of Alkenes: Mechanistic, Crystallographic, and Computational Studies

PubMed Central

Denmark, Scott E.; Hartmann, Eduard; Kornfilt, David J. P.; Wang, Hao

2015-01-01

The stereocontrolled introduction of vicinal heteroatomic substituents into organic molecules is one of the most powerful ways of adding value and function. Whereas many methods exist for the introduction of oxygen- and nitrogen-containing substituents, the number stereocontrolled methods for the introduction of sulfur-containing substituents pales by comparison. Previous reports from these laboratories have described the sulfenofunctionalization of alkenes that construct vicinal carbon-sulfur and carbon-oxygen, carbon-nitrogen as well as carbon-carbon bonds with high levels of diastereospecificity and enantioselectivity. This process is enabled by the concept of Lewis base activation of Lewis acids that provides activation of Group 16 electrophiles. To provide a foundation for expansion of substrate scope and improved selectivities, we have undertaken a comprehensive study of the catalytically active species. Insights gleaned from kinetic, crystallographic and computational methods have led to the introduction of a new family of sulfenylating agents that provide significantly enhanced selectivities. PMID:25411883

Channeling by Proximity: The Catalytic Advantages of Active Site Colocalization Using Brownian Dynamics.

PubMed

Bauler, Patricia; Huber, Gary; Leyh, Thomas; McCammon, J Andrew

2010-05-06

Nature often colocalizes successive steps in a metabolic pathway. Such organization is predicted to increase the effective concentration of pathway intermediates near their recipient active sites and to enhance catalytic efficiency. Here, the pathway of a two-step reaction is modeled using a simple spherical approximation for the enzymes and substrate particles. Brownian dynamics are used to simulate the trajectory of a substrate particle as it diffuses between the active site zones of two different enzyme spheres. The results approximate distances for the most effective reaction pathways, indicating that the most effective reaction pathway is one in which the active sites are closely aligned. However, when the active sites are too close, the ability of the substrate to react with the first enzyme was hindered, suggesting that even the most efficient orientations can be improved for a system that is allowed to rotate or change orientation to optimize the likelihood of reaction at both sites.

Enhancement of the catalytic activity of Pt nanoparticles toward methanol electro-oxidation using doped-SnO2 supporting materials

NASA Astrophysics Data System (ADS)

Merati, Zohreh; Basiri Parsa, Jalal

2018-03-01

Catalyst supports play important role in governing overall catalyst activity and durability. In this study metal oxides (SnO2, Sb and Nb doped SnO2) were electrochemically deposited on titanium substrate (Ti) as a new support material for Pt catalyst in order to electro-oxidation of methanol. Afterward platinum nanoparticles were deposited on metal oxide film via electro reduction of platinum salt in an acidic solution. The surface morphology of modified electrodes were evaluated by field-emission scanning electron microscopy (FESEM) and energy dispersive X-ray analysis (EDX) techniques. The electro-catalytic activities of prepared electrodes for methanol oxidation reaction (MOR) and oxidation of carbon monoxide (CO) absorbed on Pt was considered with cyclic voltammetry. The results showed high catalytic activity for Pt/Nb-SnO2/Ti electrode. The electrochemical surface area (ECSA) of a platinum electro-catalyst was determined by hydrogen adsorption. Pt/Nb-SnO2/Ti electrode has highest ECSA compared to other electrode resulting in high activity toward methanol electro-oxidation and CO stripping experiments. The doping of SnO2 with Sb and Nb improved ECSA and MOR activity, which act as electronic donors to increase electronic conductivity.

Antimicrobial activities of four Tunisian Chrysanthemum species.

PubMed

Sassi, Ahlem Ben; Harzallah-Skhiri, Fethia; Bourgougnon, Nathalie; Aouni, Mahjoub

2008-02-01

Tunisian Chrysanthemum species are known to have medicinal activity and some of the species are used in traditional medicine. We have earlier shown the use of C. trifurcatum flowerheads in Tunisian traditional medicine to treat constipation. In the present study we investigated the anti microbiol activity of four Tunision Chrysanthemum species. Different parts (flowers, leaves, stems, roots, leaves and flowers and leaves and stems) of four Tunisian Chrysanthemum species, were extracted with solvents of increasing polarity to obtain aqueous and organic extracts. These extracts were tested in vitro for their antimicrobial activity against 14 bacteria and four yeasts, using agar diffusion and microdilution methods. Activity was evaluated by measuring the zones of inhibition against the tested organisms and minimum inhibitory concentrations (MIC) were determined from the lowest concentrations of extracts to inhibit the growth of microorganisms. Cytotoxity and antiviral activities against Herpes simplex virus type 1 (HSV-1), were evaluated using the neutral red incorporation method. Extracts of the 4 Chrysanthemum species showed some degree of activity against one or more of the microbial strains with MIC ranging from 0.625 to 1.25 mg/ml. Most of the extracts were well tolerated by Vero cells with CC(50) > 500 microg/ml. The petroleum ether extract of C. trifurcatum stems and leaves protected infected cells with EC(50) of 100 microg/ml. Our findings showed that some Chrysanthemum extracts exhibited antimicrobial and/or anti-HSV-1 activities. Further studies aimed to the isolation and identification of active substances from the extracts which exhibited interest activities, need to be done.

Spectroscopic, Electrochemical and Computational Characterisation of Ru Species Involved in Catalytic Water Oxidation: Evidence for a [Ru(V) (O)(Py2 (Me) tacn)] Intermediate.

PubMed

Casadevall, Carla; Codolà, Zoel; Costas, Miquel; Lloret-Fillol, Julio

2016-07-11

A new family of ruthenium complexes based on the N-pentadentate ligand Py2 (Me) tacn (N-methyl-N',N''-bis(2-picolyl)-1,4,7-triazacyclononane) has been synthesised and its catalytic activity has been studied in the water-oxidation (WO) reaction. We have used chemical oxidants (ceric ammonium nitrate and NaIO4 ) to generate the WO intermediates [Ru(II) (OH2 )(Py2 (Me) tacn)](2+) , [Ru(III) (OH2 )(Py2 (Me) tacn)](3+) , [Ru(III) (OH)(Py2 (Me) tacn)](2+) and [Ru(IV) (O)(Py2 (Me) tacn)](2+) , which have been characterised spectroscopically. Their relative redox and pH stability in water has been studied by using UV/Vis and NMR spectroscopies, HRMS and spectroelectrochemistry. [Ru(IV) (O)(Py2 (Me) tacn)](2+) has a long half-life (>48 h) in water. The catalytic cycle of WO has been elucidated by using kinetic, spectroscopic, (18) O-labelling and theoretical studies, and the conclusion is that the rate-determining step is a single-site water nucleophilic attack on a metal-oxo species. Moreover, [Ru(IV) (O)(Py2 (Me) tacn)](2+) is proposed to be the resting state under catalytic conditions. By monitoring Ce(IV) consumption, we found that the O2 evolution rate is redox-controlled and independent of the initial concentration of Ce(IV) . Based on these facts, we propose herein that [Ru(IV) (O)(Py2 (Me) tacn)](2+) is oxidised to [Ru(V) (O)(Py2 (Me) tacn)](2+) prior to attack by a water molecule to give [Ru(III) (OOH)(Py2 (Me) tacn)](2+) . Finally, it is shown that the difference in WO reactivity between the homologous iron and ruthenium [M(OH2 )(Py2 (Me) tacn)](2+) (M=Ru, Fe) complexes is due to the difference in the redox stability of the key M(V) (O) intermediate. These results contribute to a better understanding of the WO mechanism and the differences between iron and ruthenium complexes in WO reactions. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Enhanced Intrinsic Catalytic Activity of λ-MnO2 by Electrochemical Tuning and Oxygen Vacancy Generation.

PubMed

Lee, Sanghan; Nam, Gyutae; Sun, Jie; Lee, Jang-Soo; Lee, Hyun-Wook; Chen, Wei; Cho, Jaephil; Cui, Yi

2016-07-18

Chemically prepared λ-MnO2 has not been intensively studied as a material for metal-air batteries, fuel cells, or supercapacitors because of their relatively poor electrochemical properties compared to α- and δ-MnO2 . Herein, through the electrochemical removal of lithium from LiMn2 O4 , highly crystalline λ-MnO2 was prepared as an efficient electrocatalyst for the oxygen reduction reaction (ORR). The ORR activity of the material was further improved by introducing oxygen vacancies (OVs) that could be achieved by increasing the calcination temperature during LiMn2 O4 synthesis; a concentration of oxygen vacancies in LiMn2 O4 could be characterized by its voltage profile as the cathode in a lithiun-metal half-cell. λ-MnO2-z prepared with the highest OV exhibited the highest diffusion-limited ORR current (5.5 mA cm(-2) ) among a series of λ-MnO2-z electrocatalysts. Furthermore, the number of transferred electrons (n) involved in the ORR was >3.8, indicating a dominant quasi-4-electron pathway. Interestingly, the catalytic performances of the samples were not a function of their surface areas, and instead depended on the concentration of OVs, indicating enhancement in the intrinsic catalytic activity of λ-MnO2 by the generation of OVs. This study demonstrates that differences in the electrochemical behavior of λ-MnO2 depend on the preparation method and provides a mechanism for a unique catalytic behavior of cubic λ-MnO2 . © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Ordered micro/macro porous K-OMS-2/SiO2 nanocatalysts: Facile synthesis, low cost and high catalytic activity for diesel soot combustion

PubMed Central

Yu, Xuehua; Zhao, Zhen; Wei, Yuechang; Liu, Jian

2017-01-01

A series of novel oxide catalysts, which contain three-dimensionally ordered macroporous (3DOM) and microporous structure, were firstly designed and successfully synthesized by simple method. In the as-prepared catalysts, 3DOM SiO2 is used as support and microporous K-OMS-2 oxide nanoparticles are supported on the wall of SiO2. 3DOM K-OMS-2/SiO2 oxide catalysts were firstly used in soot particle oxidation reaction and they show very high catalytic activities. The high activities of K-OMS-2/SiO2 oxide catalysts can be assigned to three possible reasons: macroporous effect of 3DOM structure for improving contact between soot and catalyst, microporous effect of K-OMS-2 for adsorption of small gas molecules and interaction of K and Mn for activation of gas molecules. The catalytic activities of catalysts are comparable to or even higher than noble metal catalyst in the medium and high temperature range. For example, the T50 of K-OMS-2/SiO2-50, 328 °C, is much lower than those of Pt/Al2O3 and 3DOM Au/LaFeO3, 464 and 356 °C,respectively. Moreover, catalysts exhibited high catalytic stability. It is attributed to that the K+ ions are introduced into the microporous structure of OMS-2 and stabilized in the catalytic reaction. Meanwhile, the K+ ions play an important role in templating and stabilizing the tunneled framework of OMS-2. PMID:28443610

Highly Oriented Growth of Catalytically Active Zeolite ZSM-5 Films with a Broad Range of Si/Al Ratios.

PubMed

Fu, Donglong; Schmidt, Joel E; Ristanović, Zoran; Chowdhury, Abhishek Dutta; Meirer, Florian; Weckhuysen, Bert M

2017-09-04

Highly b-oriented zeolite ZSM-5 films are critical for applications in catalysis and separations and may serve as models to study diffusion and catalytic properties in single zeolite channels. However, the introduction of catalytically active Al 3+ usually disrupts the orientation of zeolite films. Herein, using structure-directing agents with hydroxy groups, we demonstrate a new method to prepare highly b-oriented zeolite ZSM-5 films with a broad range of Si/Al ratios (Si/Al=45 to ∞). Fluorescence micro-(spectro)scopy was used to monitor misoriented microstructures, which are invisible to X-ray diffraction, and show Al 3+ framework incorporation and illustrate the differences between misoriented and b-oriented films. The methanol-to-hydrocarbons process was studied by operando UV/Vis diffuse reflectance micro-spectroscopy with on-line mass spectrometry, showing that the b-oriented zeolite ZSM-5 films are active and stable under realistic process conditions. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

Highly Oriented Growth of Catalytically Active Zeolite ZSM‐5 Films with a Broad Range of Si/Al Ratios

PubMed Central

Fu, Donglong; Schmidt, Joel E.; Ristanović, Zoran; Chowdhury, Abhishek Dutta; Meirer, Florian

2017-01-01

Abstract Highly b‐oriented zeolite ZSM‐5 films are critical for applications in catalysis and separations and may serve as models to study diffusion and catalytic properties in single zeolite channels. However, the introduction of catalytically active Al3+ usually disrupts the orientation of zeolite films. Herein, using structure‐directing agents with hydroxy groups, we demonstrate a new method to prepare highly b‐oriented zeolite ZSM‐5 films with a broad range of Si/Al ratios (Si/Al=45 to ∞). Fluorescence micro‐(spectro)scopy was used to monitor misoriented microstructures, which are invisible to X‐ray diffraction, and show Al3+ framework incorporation and illustrate the differences between misoriented and b‐oriented films. The methanol‐to‐hydrocarbons process was studied by operando UV/Vis diffuse reflectance micro‐spectroscopy with on‐line mass spectrometry, showing that the b‐oriented zeolite ZSM‐5 films are active and stable under realistic process conditions. PMID:28675590

One-step fabrication of large-area ultrathin MoS2 nanofilms with high catalytic activity for photovoltaic devices.

PubMed

Liang, Jia; Li, Jia; Zhu, Hongfei; Han, Yuxiang; Wang, Yanrong; Wang, Caixing; Jin, Zhong; Zhang, Gengmin; Liu, Jie

2016-09-21

Here we report a facile one-step solution-phase process to directly grow ultrathin MoS2 nanofilms on a transparent conductive glass as a novel high-performance counter electrode for dye-sensitized solar cells. After an appropriate reaction time, the entire surface of the conductive glass substrate was uniformly covered by ultrathin MoS2 nanofilms with a thickness of only several stacked layers. Electrochemical impedance spectroscopy and cyclic voltammetry reveal that the MoS2 nanofilms possess excellent catalytic activity towards tri-iodide reduction. When used in dye-sensitized solar cells, the MoS2 nanofilms show an impressive energy conversion efficiency of 8.3%, which is higher than that of a Pt-based electrode and very promising to be a desirable alternative counter electrode. Considering their ultrathin thickness, superior catalytic activity, simple preparation process and low cost, the as-prepared MoS2 nanofilms with high photovoltaic performance are expected to be widely employed in dye-sensitized solar cells.

Green synthesis of gold nanoparticles using Trigonella foenum-graecum and its size-dependent catalytic activity

NASA Astrophysics Data System (ADS)

Aswathy Aromal, S.; Philip, Daizy

2012-11-01

The development of new synthesis methods for monodispersed nanocrystals using cheap and nontoxic chemicals, environmentally benign solvents and renewable materials remains a challenge to the scientific community. Most of the current methods involve known protocols which may be potentially harmful to either environment or human health. Recent research has been focused on green synthesis methods to produce new nanomaterials, ecofriendly and safer with sustainable commercial viability. The present work reports the green synthesis of gold nanoparticles using the aqueous extract of fenugreek (Trigonella foenum-graecum) as reducing and protecting agent. The pathway is based on the reduction of AuCl4- by the extract of fenugreek. This method is simple, efficient, economic and nontoxic. Gold nanoparticles having different sizes in the range from 15 to 25 nm could be obtained by controlling the synthesis parameters. The nanoparticles have been characterized by UV-Visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD) and FTIR analysis. The high crystallinity of nanoparticles is evident from clear lattice fringes in the HRTEM images, bright circular spots in the SAED pattern and peaks in the XRD pattern. FTIR spectrum indicates the presence of different functional groups present in the biomolecule capping the nanoparticles. The synthesized gold nanoparticles show good catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol by excess NaBH4. The catalytic activity is found to be size-dependent, the smaller nanoparticles showing faster activity.

Boosting Chemical Stability, Catalytic Activity, and Enantioselectivity of Metal-Organic Frameworks for Batch and Flow Reactions.

PubMed

Chen, Xu; Jiang, Hong; Hou, Bang; Gong, Wei; Liu, Yan; Cui, Yong

2017-09-27

A key challenge in heterogeneous catalysis is the design and synthesis of heterogeneous catalysts featuring high catalytic activity, selectivity, and recyclability. Here we demonstrate that high-performance heterogeneous asymmetric catalysts can be engineered from a metal-organic framework (MOF) platform by using a ligand design strategy. Three porous chiral MOFs with the framework formula [Mn 2 L(H 2 O) 2 ] are prepared from enantiopure phosphono-carboxylate ligands of 1,1'-biphenol that are functionalized with 3,5-bis(trifluoromethyl)-, bismethyl-, and bisfluoro-phenyl substituents at the 3,3'-position. For the first time, we show that not only chemical stability but also catalytic activity and stereoselectivity of the MOFs can be tuned by modifying the ligand structures. Particularly, the MOF incorporated with -CF 3 groups on the pore walls exhibits enhanced tolerance to water, weak acid, and base compared with the MOFs with -F and -Me groups. Under both batch and flow reaction systems, the CF 3 -containing MOF demonstrated excellent reactivity, selectivity, and recyclability, affording high yields and enantioselectivities for alkylations of indoles and pyrrole with a range of ketoesters or nitroalkenes. In contrast, the corresponding homogeneous catalysts gave low enantioselectivity in catalyzing the tested reactions.

Theoretical and experimental insights into the origin of the catalytic activity of subnanometric gold clusters: attempts to predict reactivity with clusters and nanoparticles of gold.

PubMed

Boronat, Mercedes; Leyva-Pérez, Antonio; Corma, Avelino

2014-03-18

Particle size is one of the key parameters determining the unexpected catalytic activity of gold, with reactivity improving as the particle gets smaller. While this is valid in the 1-5 nm range, chemists are now investigating the influence of particle size in the subnanometer regime. This is due to recent advances in both characterization techniques and synthetic routes capable of stabilizing these size-controlled gold clusters. Researchers reported in early studies that small clusters or aggregates of a few atoms can be extremely active in some reactions, while 1-2 nm nanoparticles are catalytically more efficient for other reactions. Furthermore, the possibility that small gold clusters generated in situ from gold salts or complexes could be the real active species in homogeneous gold-catalyzed organic reactions should be considered. In this Account, we address two questions. First, what is the origin of the enhanced reactivity of gold clusters on the subnanometer scale? And second, how can we predict the reactions where small clusters should work better than larger nanoparticles? Both geometric factors and electronic or quantum size effects become important in the subnanometer regime. Geometric reasons play a key role in hydrogenation reactions, where only accessible low coordinated neutral Au atoms are needed to dissociate H2. The quantum size effects of gold clusters are important as well, as clusters formed by only a few atoms have discrete molecule-like electronic states and their chemical reactivity is related to interactions between the cluster's frontier molecular orbitals and those of the reactant molecules. From first principles calculations, we predict an enhanced reactivity of small planar clusters for reactions involving activation of CC multiple bonds in alkenes and alkynes through Lewis acid-base interactions, and a better catalytic performance of 3D gold nanoparticles in redox reactions involving bond dissociation by oxidative addition and new

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

The Catalytic and Non-catalytic Functions of the Brahma Chromatin-Remodeling Protein Collaborate to Fine-Tune Circadian Transcription in Drosophila

PubMed Central

Kwok, Rosanna S.; Li, Ying H.; Lei, Anna J.; Edery, Isaac; Chiu, Joanna C.

2015-01-01

Daily rhythms in gene expression play a critical role in the progression of circadian clocks, and are under regulation by transcription factor binding, histone modifications, RNA polymerase II (RNAPII) recruitment and elongation, and post-transcriptional mechanisms. Although previous studies have shown that clock-controlled genes exhibit rhythmic chromatin modifications, less is known about the functions performed by chromatin remodelers in animal clockwork. Here we have identified the Brahma (Brm) complex as a regulator of the Drosophila clock. In Drosophila, CLOCK (CLK) is the master transcriptional activator driving cyclical gene expression by participating in an auto-inhibitory feedback loop that involves stimulating the expression of the main negative regulators, period (per) and timeless (tim). BRM functions catalytically to increase nucleosome density at the promoters of per and tim, creating an overall restrictive chromatin landscape to limit transcriptional output during the active phase of cycling gene expression. In addition, the non-catalytic function of BRM regulates the level and binding of CLK to target promoters and maintains transient RNAPII stalling at the per promoter, likely by recruiting repressive and pausing factors. By disentangling its catalytic versus non-catalytic functions at the promoters of CLK target genes, we uncovered a multi-leveled mechanism in which BRM fine-tunes circadian transcription. PMID:26132408

Elastase-like Activity Is Dominant to Chymotrypsin-like Activity in 20S Proteasome's β5 Catalytic Subunit.

PubMed

Bensinger, Dennis; Neumann, Theresa; Scholz, Christoph; Voss, Constantin; Knorr, Sabine; Kuckelkorn, Ulrike; Hamacher, Kay; Kloetzel, Peter-Michael; Schmidt, Boris

2016-07-15

The ubiquitin/proteasome system is the major protein degradation pathway in eukaryotes with several key catalytic cores. Targeting the β5 subunit with small-molecule inhibitors is an established therapeutic strategy for hematologic cancers. Herein, we report a mouse-trap-like conformational change that influences molecular recognition depending on the substitution pattern of a bound ligand. Variation of the size of P1 residues from the highly β5-selective proteasome inhibitor BSc2118 allows for discrimination between inhibitory strength and substrate conversion. We found that increasing molecular size strengthens inhibition, whereas decreasing P1 size accelerates substrate conversion. Evaluation of substrate hydrolysis after silencing of β5 activity reveals significant residual activity for large residues exclusively. Thus, classification of the β5 subunit as chymotrypsin-like and the use of the standard tyrosine-containing substrate should be reconsidered.

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

PubMed

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

2017-06-01

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

Demonstration of a Catalytic Converter Using a Lawn Mower Engine

ERIC Educational Resources Information Center

Young, Mark A.

2010-01-01

Catalytic conversion is an important tool in environmental-remediation strategies and source removal of pollutants. Because a catalyst is regenerated, the chemistry can be extremely effective for conversion of undesirable pollutant species to less harmful products in situations where the pollutants have accumulated or are being continuously…

Citric acid induced promoted dispersion of Pt on the support and enhanced catalytic activities for a Pt-based catalyst

NASA Astrophysics Data System (ADS)

Cheng, Tianqiong; Wang, Jianli; Wang, Suning; Cui, Yajuan; Zhang, Hailong; Yan, Shuang; Yuan, Shandong; Chen, Yaoqiang

2017-12-01

Citric acid (CA), as the chelating agent, was introduced to obtain the enhanced Pt dispersion and catalytic activities for the Pt-based catalysts supported on oxygen-storage material. The role and content of CA were investigated systematically. It was found that the citric acid-assisted catalysts showed better Pt dispersion and smaller nanoparticle size of Pt. Thus, the catalyst had lower reduction temperature, preferable thermostability and possessed more oxidation state of Pt species under the oxidation atmosphere. The citric acid-induced fresh catalysts were excellent to convert CO and the corresponding aged ones exhibited higher activities for the elimination of all the target pollutants. Among the aged catalysts, P2-a (the mole ratio of Pt/CA is 2:1) presented the best performance. Particularly, compared with the reference sample (Pc-a), the light-off temperatures (T50) of NO, HC and CO for P2-a decreased by 39 °C, 42 °C and 72 °C, respectively, and the full-conversion temperatures (T90) of NO, HC and CO for P2-a decreased by 44 °C, 44 °C and 48 °C, respectively. Therefore, this work provides a facile and valid method to manufacture advanced catalysts for purification of the vehicle exhaust in the future.

A trade off between catalytic activity and protein stability determines the clinical manifestations of glucose-6-phosphate dehydrogenase (G6PD) deficiency.

PubMed

Boonyuen, Usa; Chamchoy, Kamonwan; Swangsri, Thitiluck; Junkree, Thanyaphorn; Day, Nicholas P J; White, Nicholas J; Imwong, Mallika

2017-11-01

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common polymorphism and enzymopathy in humans, affecting approximately 400 million people worldwide. It is responsible for various clinical manifestations, including favism, hemolytic anemia, chronic non-spherocytic hemolytic anemia, spontaneous abortion, and neonatal hyperbilirubinemia. Understanding the molecular mechanisms underlying the severity of G6PD deficiency is of great importance but that of many G6PD variants are still unknown. In this study, we report the construction, expression, purification, and biochemical characterization in terms of kinetic properties and stability of five clinical G6PD variants-G6PD Bangkok, G6PD Bangkok noi, G6PD Songklanagarind, G6PD Canton+Bangkok noi, and G6PD Union+Viangchan. G6PD Bangkok and G6PD Canton+Bangkok noi showed a complete loss of catalytic activity and moderate reduction in thermal stability when compared with the native G6PD. G6PD Bangkok noi and G6PD Union+Viangchan showed a significant reduction in catalytic efficiency, whereas G6PD Songklanagarind showed a catalytic activity comparable to the wild-type enzyme. The Union+Viangchan mutation showed a remarkable effect on the global stability of the enzyme. In addition, our results indicate that the location of mutations in G6PD variants affects their catalytic activity, stability, and structure. Hence, our results provide a molecular explanation for clinical manifestations observed in individuals with G6PD deficiency. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

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

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

Tassi, Marco; Bartollini, Elena; Adriaensens, Peter

2015-12-07

In view of searching for efficient polymeric supports for organic bases to be used in environmentally friendly reaction conditions, novel gel-type cross-linked polystyrenes functionalized with diethylamine and 1,5,7-triazabicyclo[4.4.0]dec-5-ene, have been prepared. Moreover, the structural properties and morphology of these catalysts have been determined by extensive solid state NMR experiments, FTIR spectroscopy and SEM/TEM microscopy. SPACeR-supported bases were found to exhibit high catalytic activity in the epoxide ring opening by phenols. Finally, a range of β-substituted alcohols have been readily and regioselectively synthesized.

Producing carbon-based boundary films from catalytically active lubricant additives

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

Erdemir, Ali; Mane, Anil U.; Elam, Jeffrey W.

A lubricant composition includes an oil including a plurality of long-chain hydrocarbon molecules. A quantity of a catalytically active metal-organic additive is mixed with the oil. The metal-organic additive is formulated to fragment the long-chain hydrocarbon molecules of the oil into at least one of dimers and trimers under the influence of at least one of a mechanical loading and a thermal loading. In some embodiments, the metal-organic additive includes a compound of formula II: ##STR00001## where: X is Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, Hf,more » Ta, W, Re, Os, Ir, Pt, Au, Hg, Rf, Db, Sg, Bh, Hs, Mt, Ds, Rg or Cn, and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are alkyl or alkyl halide.« less

Catalytic, hollow, refractory spheres, conversions with them

NASA Technical Reports Server (NTRS)

Wang, Taylor G. (Inventor); Elleman, Daniel D. (Inventor); Lee, Mark C. (Inventor); Kendall, Jr., James M. (Inventor)

1989-01-01

Improved, heterogeneous, refractory catalysts are in the form of gas-impervious, hollow, thin-walled spheres (10) suitable formed of a shell (12) of refractory such as alumina having a cavity (14) containing a gas at a pressure greater than atmospheric pressure. The wall material may be itself catalytic or a catalytically active material coated onto the sphere as a layer (16), suitably platinum or iron, which may be further coated with a layer (18) of activator or promoter. The density of the spheres (30) can be uniformly controlled to a preselected value within .+-.10 percent of the density of the fluid reactant such that the spheres either remain suspended or slowly fall or rise through the liquid reactant.

Catalytic Oxidation of Methane into Methanol over Copper-Exchanged Zeolites with Oxygen at Low Temperature

PubMed Central

2016-01-01

The direct catalytic conversion of methane to liquid oxygenated compounds, such as methanol or dimethyl ether, at low temperature using molecular oxygen is a grand challenge in C–H activation that has never been met with synthetic, heterogeneous catalysts. We report the first demonstration of direct, catalytic oxidation of methane into methanol with molecular oxygen over copper-exchanged zeolites at low reaction temperatures (483–498 K). Reaction kinetics studies show sustained catalytic activity and high selectivity for a variety of commercially available zeolite topologies under mild conditions (e.g., 483 K and atmospheric pressure). Transient and steady state measurements with isotopically labeled molecules confirm catalytic turnover. The catalytic rates and apparent activation energies are affected by the zeolite topology, with caged-based zeolites (e.g., Cu-SSZ-13) showing the highest rates. Although the reaction rates are low, the discovery of catalytic sites in copper-exchanged zeolites will accelerate the development of strategies to directly oxidize methane into methanol under mild conditions. PMID:27413787

Correlation Between the Extent of Catalytic Activity and Charge Density of Montmorillonites

PubMed Central

Steudel, Annett; Emmerich, Katja; Lagaly, Gerhard; Schuhmann, Rainer

2010-01-01

Abstract The clay mineral montmorillonite is a member of the phyllosilicate group of minerals, which has been detected on martian soil. Montmorillonite catalyzes the condensation of activated monomers to form RNA-like oligomers. Extent of catalysis, that is, the yield of oligomers, and the length of the longest oligomer formed in these reactions widely varies with the source of montmorillonite (i.e., the locality where the mineral is mined). This study was undertaken to establish whether there exists a correlation between the extent of catalytic property and the charge density of montmorillonites. Charge density was determined by saturating the montmorillonites with alkyl ammonium cations that contained increasing lengths of alkyl chains, [CH3-(CH2)n-NH3]+, where n = 3–16 and 18, and then measuring d(001), interlayer spacing of the resulting montmorillonite-alkyl ammonium-montmorillonite complex by X-ray diffractometry (XRD). Results demonstrate that catalytic activity of montmorillonites with lower charge density is superior to that of higher charge density montmorillonite. They produce longer oligomers that contain 9 to 10 monomer units, while montmorillonite with high charge density catalyzes the formation of oligomers that contain only 4 monomer units. The charge density of montmorillonites can also be calculated from the chemical composition if elemental analysis data of the pure mineral are available. In the next mission to Mars, CheMin (Chemistry and Mineralogy), a combined X-ray diffraction/X-ray fluorescence instrument, will provide information on the mineralogical and elemental analysis of the samples. Possible significance of these results for planning the future missions to Mars for the search of organic compounds and extinct or extant life is discussed. Key Words: Mars—Origin of life—Montmorillonite—Mineral catalysis—Layer charge density—X–ray diffractometry. Astrobiology 10, 743–749. PMID:20854214

Synthesis of hierarchically porous perovskite-carbon aerogel composite catalysts for the rapid degradation of fuchsin basic under microwave irradiation and an insight into probable catalytic mechanism

NASA Astrophysics Data System (ADS)

Wang, Yin; Wang, Jiayuan; Du, Baobao; Wang, Yun; Xiong, Yang; Yang, Yiqiong; Zhang, Xiaodong

2018-05-01

3D hierarchically porous perovskites LaFe0.5M0.5O3-CA (M = Mn, Cu) were synthesized by a two-step method using PMMA as template and supporting with carbon aerogel, which were characterized with SEM, TEM, XRD, XPS and FT-IR spectroscopy. The as-prepared composites were used in microwave (MW) catalytic degradation of fuchsin basic (FB) dye wastewater. Batch experiment results showed that the catalytic degradation of FB could be remarkably improved by coating with CA. And LaFe0.5Cu0.5O3-CA exhibited higher catalytic performance than LaFe0.5Mn0.5O3-CA, which had a close connection with the activity of substitution metal ion in B site of the catalysts. The FB removal fit pseudo-first-order model and the degradation rate constant increased with initial pH value and MW powder while decreases with initial FB concentration. All catalysts presented favorable recycling and stability in the repeated experiment. Radical scavenger measurements indicated that hydroxyl radicals rather than surface peroxide and hole played an important role in the catalytic process, and its quantity determined the degradation of FB. Furthermore, both Cu and Fe species were involved in the formation of active species, which were responsible to the excellent performance of the LaFe0.5Cu0.5O3-CA/MW system. Therefore, LaFe0.5Cu0.5O3-CA/MW showed to be a promising technology for the removal of organic pollutants in wastewater treatment applications.

Atomically Precise Metal Nanoclusters for Catalytic Application

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

Jin, Rongchao

2016-11-18

The central goal of this project is to explore the catalytic application of atomically precise gold nanoclusters. By solving the total structures of ligand-protected nanoclusters, we aim to correlate the catalytic properties of metal nanoclusters with their atomic/electronic structures. Such correlation unravel some fundamental aspects of nanocatalysis, such as the nature of particle size effect, origin of catalytic selectivity, particle-support interactions, the identification of catalytically active centers, etc. The well-defined nanocluster catalysts mediate the knowledge gap between single crystal model catalysts and real-world conventional nanocatalysts. These nanoclusters also hold great promise in catalyzing certain types of reactions with extraordinarily highmore » selectivity. These aims are in line with the overall goals of the catalytic science and technology of DOE and advance the BES mission “to support fundamental research to understand, predict, and ultimately control matter and energy at the level of electrons, atoms, and molecules”. Our group has successfully prepared different sized, robust gold nanoclusters protected by thiolates, such as Au 25(SR) 18, Au 28(SR) 20, Au 38(SR) 24, Au 99(SR) 42, Au 144(SR) 60, etc. Some of these nanoclusters have been crystallographically characterized through X-ray crystallography. These ultrasmall nanoclusters (< 2 nm diameter) exhibit discrete electronic structures due to quantum size effect, as opposed to quasicontinuous band structure of conventional metal nanoparticles or bulk metals. The available atomic structures (metal core plus surface ligands) of nanoclusters serve as the basis for structure-property correlations. We have investigated the unique catalytic properties of nanoclusters (i.e. not observed in conventional nanogold catalysts) and revealed the structure-selectivity relationships. Highlights of our works include: i) Effects of ligand, cluster charge state, and size on the catalytic

Identification of the haemolytic activity of Malassezia species.

PubMed

Juntachai, Weerapong; Kummasook, Aksarakorn; Mekaprateep, Malee; Kajiwara, Susumu

2014-03-01

Malassezia species are part of the normal skin flora and are associated with a number of human and animal skin diseases. However, the mechanisms that mediate infection and host-fungal interactions are poorly understood. The haemolytic activity of several microorganisms is considered a factor that contributes to pathogenicity of the organism to humans and animals. This virulence factor was previously identified in several pathogenic fungi that cause systemic mycoses, such as Aspergillus and Candida. In this study, the haemolytic activity of six major Malassezia species, including M. furfur, M. globosa, M. pachydermatis, M. restricta, M. slooffiae and M. sympodialis, was investigated. The haemolytic activity of these species was tested on tryptone soya agar with 5% sheep blood. All the examined Malassezia species produced a halo zone of complete haemolysis. A quantitative analysis of the haemolytic activity was performed by incubating sheep erythrocytes with the extraction from culture of each Malassezia species. Interestingly, M. globosa and M. restricta showed significantly high haemolytic activity compared with the other Malassezia species. In addition, M. globosa also exhibited stable haemolytic activity after treatment at 100 °C and in the presence of some proteases, indicating that this haemolytic factor is different from those of other fungi. © 2013 Blackwell Verlag GmbH.

Catalytic Properties and Biomedical Applications of Cerium Oxide Nanoparticles

PubMed Central

Walkey, Carl; Das, Soumen; Seal, Sudipta; Erlichman, Joseph; Heckman, Karin; Ghibelli, Lina; Traversa, Enrico; McGinnis, James F.; Self, William T.

2014-01-01

Cerium oxide nanoparticles (Nanoceria) have shown promise as catalytic antioxidants in the test tube, cell culture models and animal models of disease. However given the reactivity that is well established at the surface of these nanoparticles, the biological utilization of Nanoceria as a therapeutic still poses many challenges. Moreover the form that these particles take in a biological environment, such as the changes that can occur due to a protein corona, are not well established. This review aims to summarize the existing literature on biological use of Nanoceria, and to raise questions about what further study is needed to apply this interesting catalytic material to biomedical applications. These questions include: 1) How does preparation, exposure dose, route and experimental model influence the reported effects of Nanoceria in animal studies? 2) What are the considerations to develop Nanoceria as a therapeutic agent in regards to these parameters? 3) What biological targets of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are relevant to this targeting, and how do these properties also influence the safety of these nanomaterials? PMID:26207185

Mechanism of TRIM25 Catalytic Activation in the Antiviral RIG-I Pathway.

PubMed

Sanchez, Jacint G; Chiang, Jessica J; Sparrer, Konstantin M J; Alam, Steven L; Chi, Michael; Roganowicz, Marcin D; Sankaran, Banumathi; Gack, Michaela U; Pornillos, Owen

2016-08-02

Antiviral response pathways induce interferon by higher-order assembly of signaling complexes called signalosomes. Assembly of the RIG-I signalosome is regulated by K63-linked polyubiquitin chains, which are synthesized by the E3 ubiquitin ligase, TRIM25. We have previously shown that the TRIM25 coiled-coil domain is a stable, antiparallel dimer that positions two catalytic RING domains on opposite ends of an elongated rod. We now show that the RING domain is a separate self-association motif that engages ubiquitin-conjugated E2 enzymes as a dimer. RING dimerization is required for catalysis, TRIM25-mediated RIG-I ubiquitination, interferon induction, and antiviral activity. We also provide evidence that RING dimerization and E3 ligase activity are promoted by binding of the TRIM25 SPRY domain to the RIG-I effector domain. These results indicate that TRIM25 actively participates in higher-order assembly of the RIG-I signalosome and helps to fine-tune the efficiency of the RIG-I-mediated antiviral response. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Mechanism of TRIM25 Catalytic Activation in the Antiviral RIG-I Pathway

PubMed Central

Sanchez, Jacint G.; Chiang, Jessica J.; Sparrer, Konstantin M.J.; Alam, Steven L.; Chi, Michael; Roganowicz, Marcin D.; Sankaran, Banumathi; Gack, Michaela U.; Pornillos, Owen

2016-01-01

SUMMARY Antiviral response pathways induce interferon by higher-order assembly of signaling complexes called signalosomes. Assembly of the RIG-I signalosome is regulated by K63-linked polyubiquitin chains, which are synthesized by the E3 ubiquitin ligase, TRIM25. We have previously shown that the TRIM25 coiled-coil domain is a stable, antiparallel dimer that positions two catalytic RING domains on opposite ends of an elongated rod. We now show that the RING domain is a separate self-association motif that engages ubiquitin-conjugated E2 enzymes as a dimer. RING dimerization is required for catalysis, TRIM25-mediated RIG-I ubiquitination, interferon induction, and antiviral activity. We also provide evidence that RING dimerization and E3 ligase activity are promoted by binding of the TRIM25 SPRY domain to the RIG-I effector domain. These results indicate that TRIM25 actively participates in higher-order assembly of the RIG-I signalosome and helps to fine-tune the efficiency of the RIG-I-mediated antiviral response. PMID:27425606

Mechanism of TRIM25 Catalytic Activation in the Antiviral RIG-I Pathway

DOE PAGES

Sanchez, Jacint G.; Chiang, Jessica J.; Sparrer, Konstantin M. J.; ...

2016-07-14

Antiviral response pathways induce interferon by higher-order assembly of signaling complexes called signalosomes. Assembly of the RIG-I signalosome is regulated by K63-linked polyubiquitin chains, which are synthesized by the E3 ubiquitin ligase, TRIM25. We have previously shown that the TRIM25 coiled-coil domain is a stable, antiparallel dimer that positions two catalytic RING domains on opposite ends of an elongated rod. We now show that the RING domain is a separate self-association motif that engages ubiquitin-conjugated E2 enzymes as a dimer. RING dimerization is required for catalysis, TRIM25-mediated RIG-I ubiquitination, interferon induction, and antiviral activity. We also provide evidence that RINGmore » dimerization and E3 ligase activity are promoted by binding of the TRIM25 SPRY domain to the RIG-I effector domain. These results indicate that TRIM25 actively participates in higher-order assembly of the RIG-I signalosome and helps to fine-tune the efficiency of the RIG-I-mediated antiviral response.« less

Catalytic oxidation of waste materials

NASA Technical Reports Server (NTRS)

Jagow, R. B.

1977-01-01

Aqueous stream of human waste is mixed with soluble ruthenium salts and is introduced into reactor at temperature where ruthenium black catalyst forms on internal surfaces of reactor. This provides catalytically active surface to convert oxidizable wastes into breakdown products such as water and carbon dioxide.

Triangular Diagrams Teach Steady and Dynamic Behaviour of Catalytic Reactions.

ERIC Educational Resources Information Center

Klusacek, K.; And Others

1989-01-01

Illustrates how triangular diagrams can aid in presenting some of the rather complex transient interactions that occur among gas and surface species during heterogeneous catalytic reactions. The basic equations and numerical examples are described. Classroom use of the triangular diagram is discussed. Several diagrams and graphs are provided. (YP)

Sodium dodecyl sulfate-assisted hydrothermal synthesis of mesoporous nickel cobaltite nanoparticles with enhanced catalytic activity for methanol electrooxidation

NASA Astrophysics Data System (ADS)

Ding, Rui; Qi, Li; Jia, Mingjun; Wang, Hongyu

2014-04-01

Mesoporous nickel cobaltite (NiCo2O4) nanoparticles have been synthesized via a facile hydrothermal strategy with the assistance of sodium dodecyl sulfate (SDS) soft template (ST). Their physicochemical properties have been characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectra (EDS), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. Their electrocatalytic performances have been examined by cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained NiCo2O4 materials exhibit a typical nanoscale crystalline hexagonal morphology with specific surface area (SSA) and mesopore volume of 88.63 m2 g-1 and 0.298 cm3 g-1. Impressively, the SDS-assisted NiCo2O4 electrode shows a catalytic current density of 125 mA cm-2 and 72% retention for consecutive 1000 s at 0.6 V in 1 M KOH and 0.5 M CH3OH electrolytes towards methanol (CH3OH) electrooxidation, which is better than the one without SDS assistance. The pronounced electrocatalytic activity is largely ascribed to their higher surface intensities of Co and Ni species and superior mesoporous nanostructures, which provide the richer electroactive sites and faster electrochemical kinetics, leading to the enhanced electrocatalytic activity.

Comparison of Elemental Mercury Oxidation Across Vanadium and Cerium Based Catalysts in Coal Combustion Flue Gas: Catalytic Performances and Particulate Matter Effects.

PubMed

Wan, Qi; Yao, Qiang; Duan, Lei; Li, Xinghua; Zhang, Lei; Hao, Jiming

2018-03-06

This paper discussed the field test results of mercury oxidation activities over vanadium and cerium based catalysts in both coal-fired circulating fluidized bed boiler (CFBB) and chain grate boiler (CGB) flue gases. The characterizations of the catalysts and effects of flue gas components, specifically the particulate matter (PM) species, were also discussed. The catalytic performance results indicated that both catalysts exhibited mercury oxidation preference in CGB flue gas rather than in CFBB flue gas. Flue gas component studies before and after dust removal equipment implied that the mercury oxidation was well related to PM, together with gaseous components such as NO, SO 2 , and NH 3 . Further investigations demonstrated a negative PM concentration-induced effect on the mercury oxidation activity in the flue gases before the dust removal, which was attributed to the surface coverage by the large amount of PM. In addition, the PM concentrations in the flue gases after the dust removal failed in determining the mercury oxidation efficiency, wherein the presence of different chemical species in PM, such as elemental carbon (EC), organic carbon (OC) and alkali (earth) metals (Na, Mg, K, and Ca) in the flue gases dominated the catalytic oxidation of mercury.

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.

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

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

Ooi, Mahayatun Dayana Johan; Aziz, Azlan Abdul; Nanobiotechnology Research and Innovation

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

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.

Biosynthesis and secretion of catalytically active acetylcholinesterase in Xenopus oocytes microinjected with mRNA from rat brain and from Torpedo electric organ.

PubMed

Soreq, H; Parvari, R; Silman, I

1982-02-01

A novel technique was developed for monitoring the level of the mRNA species that direct the synthesis of acetylcholinesterase (AcChoEase; acetylcholine acetylhydrolase, EC 3.1.1.7), using microinjected Xenopus oocytes as a translation system. When injected with poly(A)-containing RNA from whole rat brain or rat cerebellum and from electric organ of Torpedo ocellata, Xenopus oocytes synthesize and secrete catalytically active cholinesterase. The newly synthesized enzyme, which is mostly secreted into the oocytes incubation medium, appears to be primarily AcChoEase because it is inhibited by the specific inhibitor BW 284C51. The new enzymatic activity can be detected after injection of as little as 12.5 ng of poly(A)-containing RNA per oocyte, and there is a linear dependence of the oocytes' ability to form AcChoEase on the amount of injected RNA. The AcChoEase mRNA displays a tau 1/2 of about 10 +/- 3 hr in injected oocytes. The abundance of AcChoEase mRNA in the total nonfractionated mRNA injected was calculated to be ca. 1 x 10(-5), a value similar to the level of AcChoEase protein determined in rat brain. The combination of the high turnover number of AcChoEase, the efficiency of the oocyte system, and the sensitivity of the assay used thus permit the accurate monitoring of the scarce mRNA species that direct the synthesis of this enzyme.

Catalytic applications of bio-inspired nanomaterials

NASA Astrophysics Data System (ADS)

Pacardo, Dennis Kien Balaong

The biomimetic synthesis of Pd nanoparticles was presented using the Pd4 peptide, TSNAVHPTLRHL, isolated from combinatorial phage display library. Using this approach, nearly monodisperse and spherical Pd nanoparticles were generated with an average diameter of 1.9 +/- 0.4 nm. The peptide-based nanocatalyst were employed in the Stille coupling reaction under energy-efficient and environmentally friendly reaction conditions of aqueous solvent, room temperature and very low catalyst loading. To this end, the Pd nanocatalyst generated high turnover frequency (TOF) value and quantitative yields using ≥ 0.005 mol% Pd as well as catalytic activities with different aryl halides containing electron-withdrawing and electron-donating groups. The Pd4-capped Pd nanoparticles followed the atom-leaching mechanism and were found to be selective with respect to substrate identity. On the other hand, the naturally-occurring R5 peptide (SSKKSGSYSGSKGSKRRIL) was employed in the synthesis of biotemplated Pd nanomaterials which showed morphological changes as a function of Pd:peptide ratio. TOF analysis for hydrogenation of olefinic alcohols showed similar catalytic activity regardless of nanomorphology. Determination of catalytic properties of these bio-inspired nanomaterials are important as they serve as model system for alternative green catalyst with applications in industrially important transformations.

Immobilizing Highly Catalytically Active Pt Nanoparticles inside the Pores of Metal-Organic Framework: A Double Solvents Approach

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

Aijaz, Arshad; Karkamkar, Abhijeet J.; Choi, Young Joon

2012-08-29

Ultrafine Pt nanoparticles were successfully immobilized inside the pores of a metal-organic framework MIL-101 without deposition of Pt nanoparticles on the external surfaces of framework by using a 'double solvents' method. The resulting Pt@MIL-101 composites with different Pt loadings represent the first highly active MOF-immobilized metal nanocatalysts for catalytic reactions in all three phases: liquid-phase ammonia borane hydrolysis; solid-phase ammonia borane thermal dehy-drogenation and gas-phase CO oxidation. The observed excellent catalytic performances are at-tributed to the small Pt nanoparticles within the pores of MIL-101. 'We are thankful to AIST and METI for financial support. TA & AK are thankful formore » support from the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. PNNL is operated by Battelle.'« less

Rich catalytic injection

DOEpatents

Veninger, Albert [Coventry, CT

2008-12-30