Highly catalytically active micro/meso-porous Ti-MCM-36 prepared by a grafting method

2017 ◽  
Vol 5 (30) ◽  
pp. 15676-15687 ◽  
Author(s):  
Chih-Cheng Chang ◽  
Jyh-Fu Lee ◽  
Soofin Cheng
Keyword(s):  
Titanium Alkoxides ◽  
Catalytic Activities ◽  
Porous Ti ◽  
Catalytically Active

The effect of titanium alkoxides as grafting agents and various solvents in the preparation of Ti(iv)-incorporated micro/meso-porous MCM-36 (Ti-MCM-36) of highly catalytic activities and reusability was examined.

scholarly journals Effect of Na2O Doping on the Surface and Catalytic Properties of the Mn2O3/Al2O3 System

1995 ◽  
Vol 12 (2) ◽  
pp. 119-128 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
S. Hammad
Keyword(s):  
Catalytic Activity ◽  
Active Sites ◽  
Catalytic Properties ◽  
Xrd Analysis ◽  
Manganese Carbonate ◽  
Oxidation Of Co ◽  
Mechanical Mixing ◽  
Catalytic Activities ◽  
Specific Catalytic Activity ◽  
Catalytically Active

Manganese/aluminium mixed oxide solids having the formula 0.2MnCO3/Al2O3 were prepared by mechanical mixing of a known weight of finely powdered manganese carbonate and aluminium hydroxide. The solids obtained were treated with NaNO3 (0.75–6 mol%) solution and dried at 110°C, then calcined in air at 500°C and 800°C for 6 h. The phases produced were identified by XRD analysis. The surface properties (SBET, Vp and r̄) of the pure and doped solids were studied by using N2 adsorption at – 196°C and their catalytic activities were determined by studying the oxidation of CO by O2at 125–300°C. The results obtained reveal that pure and doped mixed solids preheated in air at 500°C and 800°C consist of Mn2O3 (partridgite) and a poorly crystalline γ-alumina. Doping with sodium oxide at 500°C and 800°C resulted in a small decrease (14–19%) in the SBET value of the treated solids. However, this treatment brought about a significant modification in the catalytic activity of the doped solids. Doping with 0.75% Na2O at 500°C led to an increase of about 30–50% in the specific catalytic activity which was found to decrease on increasing the percentage of Na2O above this limit, falling to values smaller than that measured for the undoped catalyst. Doping at 800°C led to a progressive decrease in the activity of the treated solid to an extent proportional to the amount of dopant present. The doping process at 500°C and 800°C did not modify the mechanism of the catalytic reaction but altered the number of catalytically-active sites contributing in the catalysis of CO oxidation by O2 without changing their energetic nature.

scholarly journals Phylogenomic and Biochemical Characterization of Three Legionella pneumophila Polypeptide Deformylases

2006 ◽  
Vol 188 (14) ◽  
pp. 5249-5257 ◽  
Author(s):  
Jianzhong Huang ◽  
Glenn S. Van Aller ◽  
Amy N. Taylor ◽  
John J. Kerrigan ◽  
Wu-Schyong Liu ◽  
...  
Keyword(s):  
Legionella Pneumophila ◽  
Biochemical Characterization ◽  
Enzymatic Characterization ◽  
Genome Sequences ◽  
Catalytic Activities ◽  
Synthetic Polypeptides ◽  
Catalytically Active ◽  
Legionnaires Disease ◽  
Antibacterial Target

ABSTRACT Legionella pneumophila is a gram-negative facultative intracellular human pathogen that can cause fatal Legionnaires' disease. Polypeptide deformylase (PDF) is a novel broad-spectrum antibacterial target, and reports of inhibitors of PDF with potent activities against L. pneumophila have been published previously. Here, we report the identification of not one but three putative pdf genes, pdfA, pdfB, and pdfC, in the complete genome sequences of three strains of L. pneumophila. Phylogenetic analysis showed that L. pneumophila PdfA is most closely related to the commonly known γ-proteobacterial PDFs encoded by the gene def. PdfB and PdfC are more divergent and do not cluster with any specific bacterial or eukaryotic PDF. All three putative pdf genes from L. pneumophila strain Philadelphia 1 have been cloned, and their encoded products have been overexpressed in Escherichia coli and purified. Enzymatic characterization shows that the purified PDFs with Ni2+ substituted are catalytically active and able to remove the N-formyl group from several synthetic polypeptides, although they appear to have different substrate specificities. Surprisingly, while PdfA and PdfB with Zn2+ substituted are much less active than the Ni2+ forms of each enzyme, PdfC with Zn2+ substituted was as active as the Ni2+ form for the fMA substrate and exhibited substrate specificity different from that of Ni2+ PdfC. Furthermore, the catalytic activities of these enzymes are potently inhibited by a known small-molecule PDF inhibitor, BB-3497, which also inhibits the extracellular growth of L. pneumophila. These results indicate that even though L. pneumophila has three PDFs, they can be effectively inhibited by PDF inhibitors which can, therefore, have potent anti-L. pneumophila activity.

scholarly journals Surface and Catalytic Properties of NiO and Fe2O3 Solids

1997 ◽  
Vol 15 (8) ◽  
pp. 593-607 ◽  
Author(s):  
A. Abd. El-Aal ◽  
A.M. Ghozza ◽  
G.A. El-Shobaky
Keyword(s):  
Catalytic Activity ◽  
Calcination Temperature ◽  
Active Sites ◽  
Pore Radius ◽  
Total Pore Volume ◽  
Surface Characteristics ◽  
Oxidation Of Co ◽  
Catalytic Activities ◽  
Catalytically Active ◽  
The Mean

The surface characteristics, viz., the specific surface area SBET, the total pore volume Vp and the mean pore radius r̄, of NiO and Fe2O3 were determined from N2 adsorption isotherms conducted at −196°C for the different adsorbents preheated in air at temperatures in the range 300–800°C. The catalytic activities exhibited in CO oxidation by O2 on the various solids were investigated at temperatures varying between 150°C and 400°C. The effect of heating the NiO and Fe2O3 solids in CO and O2 atmospheres at 175–275°C on their catalytic activities was also studied. The results showed that increasing the calcination temperature in the range 300–800°C resulted in a progressive decrease in the SBET value of NiO and Fe2O3. The computed values of the apparent activation energy for the sintering of the oxides were 71 and 92 kJ/mol, respectively. The sintering of NiO and Fe2O3 took place mainly via a particle adhesion mechanism. The catalytic activity of NiO decreased progressively on increasing its calcination temperature from 300°C to 800°C, due to a decrease in its SBET value and the progressive removal of excess O2 which was present as non-stoichiometric NiO. This treatment also decreased the catalytic activity of Fe2O3. The decrease was, however, more pronounced when the temperature increased from 300°C to 400°C which was a result of the crystallization of the ferric oxide into the α-Fe2O3 phase. An increase in the calcination temperature for both oxides from 300°C to 800°C did not modify the mechanism of oxidation of CO by O2 over the various solids but rather changed the concentration of catalytically active sites. Heating NiO and Fe2O3 in CO and O2 atmospheres at 175–275°C modified their catalytic activities, with Fe2O3 being influenced to a greater extent than NiO.

scholarly journals Catalytically inactive Dnmt3b rescues mouse embryonic development by accessory and repressive functions

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Pawel Nowialis ◽  
Katarina Lopusna ◽  
Jana Opavska ◽  
Staci L. Haney ◽  
Ajay Abraham ◽  
...  
Keyword(s):  
Gene Expression ◽  
Embryonic Development ◽  
Hedgehog Signaling ◽  
Transcriptional Regulators ◽  
Dna Methyltransferases ◽  
Embryonic Lethality ◽  
Developmental Pathways ◽  
Catalytic Activities ◽  
Accessory Factor ◽  
Catalytically Active

Abstract DNA methylation regulates gene expression in a variety of processes, including mouse embryonic development. Four catalytically active enzymes function in mice as DNA methyltransferases (Dnmts) and as transcriptional regulators. Inactivation of Dnmt3b results in mouse embryonic lethality, but which activities are involved is unclear. Here we show that catalytically inactive Dnmt3b restores a majority of methylation and expression changes deregulated in the absence of Dnmt3b, and as a result, mice survive embryonic development. Thus, Dnmt3b functions as an accessory cofactor supporting catalytic activities performed by other Dnmts. We further demonstrate that Dnmt3b is linked to a control of major developmental pathways, including Wnt and hedgehog signaling. Dnmt3b directly represses Wnt9b whose aberrant up-regulation contributes to embryonic lethality of Dnmt3b knockout embryos. Our results highlight that Dnmt3b is a multifaceted protein that serves as an enzyme, an accessory factor for other methyltransferases, and as a transcriptional repressor in mouse embryogenesis.

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

1986 ◽  
Vol 102 (5) ◽  
pp. 1606-1614 ◽  
Author(s):  
D W Riches ◽  
P M Henson
Keyword(s):  
Culture Supernatant ◽  
Human Monocyte ◽  
Functional Expression ◽  
Early Response ◽  
Bacterial Lipopolysaccharide ◽  
Weak Base ◽  
Acid Hydrolases ◽  
Catalytic Activities ◽  
Complement Component C3 ◽  
Catalytically Active

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

scholarly journals Effect of Li2O Doping on the Surface and Catalytic Properties of the Cr2O/Al2O3 System

1998 ◽  
Vol 16 (6) ◽  
pp. 415-429 ◽  
Author(s):  
G.A. El-Shobaky ◽  
A.M. Ghozza ◽  
H.G. El-Shobaky
Keyword(s):  
Co Oxidation ◽  
Catalytic Reaction ◽  
Active Sites ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Maximum Increase ◽  
Exponential Factor ◽  
Catalytic Activities ◽  
Catalytically Active ◽  
Maximum Decrease

Two Cr2O3/Al2O3 samples with the nominal compositions 0.06Cr2O2/Al2O3 and 0.125Cr2O3/Al2O3 (AlCr-I and AlCr-II, respectively) were prepared by mixing a known amount of finely powdered Al(OH)3 with calculated amounts of CrO3, followed by drying at 120°C and calcination at 700°C and 800°C. Doped solid specimens were prepared by treating Al(OH)3 samples with known amounts of LiNO3 dissolved in the minimum amount of distilled water prior to mixing with CrO3. Dopant concentrations of 0.75, 1.50, 3.00 and 6.00 mol% Li2O were employed. The surface and catalytic properties of the pure and doped solids thus prepared were investigated using nitrogen adsorption at −196°C and studies of the catalysis of CO oxidation by O2 over the solid specimens at 300–400°C. The results of such studies showed that Li2O doping followed by calcination at 700°C led to a maximum increase in the specific surface area, SBET, of 26% for AlCr-I and of 55% for AlCr-II when these samples were doped with 3.00 mol% Li2O. The reverse effect was found when the calcination temperature was increased to 800°C, where a decrease of 34% in the SBET value of the AlCr-II sample doped with 3.00 mol% Li2O was detected. The catalytic activities measured at 350°C over the pure and doped solids decreased on increasing the dopant concentration, the maximum decrease in such activity being ca. 33% and 50%, respectively, for the AlCr-I and AlCr-II samples calcined at 700°C. Doping led to noticable changes in the magnitude of the activation energy for the catalytic reaction. Such changes were accompanied by parallel changes in the value of the pre-exponential factor in the Arrhenius equation. These results may indicate that Li2O doping has no effect on the mechanism of the catalytic reaction but modifies (decreases) the concentration of catalytically active sites taking part in chemisorption during the catalysis of CO oxidation by O2.

Phytochemical assisted synthesis of size and shape tunable gold nanoparticles and assessment of their catalytic activities

RSC Advances ◽  
2016 ◽  
Vol 6 (55) ◽  
pp. 49307-49316 ◽  
Author(s):  
Shreemoyee Phukan ◽  
Pankaj Bharali ◽  
Arup K. Das ◽  
Md. Harunar Rashid
Keyword(s):  
Gold Nanoparticles ◽  
Reduction Method ◽  
Catalytic Activities ◽  
Size And Shape ◽  
Catalytically Active

A faster and environmentally viable phytochemical assisted reduction method of synthesizing catalytically active gold nanoparticles (GNPs) is reported.

scholarly journals Activation Mechanism of Nickel(0) N-Heterocyclic Carbene Catalysts Stabilized by Fumarate Ligands

2021 ◽  
Author(s):  
Michael Robo ◽  
Amie Frank ◽  
Ellen Butler ◽  
Alex Nett ◽  
Santiago Canellas ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Ligand Exchange ◽  
Active Species ◽  
Heterocyclic Carbenes ◽  
Activation Mechanism ◽  
Catalyst Stability ◽  
Activation Process ◽  
Catalytic Activities ◽  
Computational Evaluation ◽  
Catalytically Active

Nickel(0) catalysts of N-heterocyclic carbenes (NHCs) that are stabilized by electronic deficient alkenes possess desirable properties of air tolerance and ease of handling while also retaining high catalytic activities. Since catalyst stability often comes at the expense of catalytic activity, we have undertaken a detailed study of the activation mechanism of a new IMes-nickel(0) catalyst stabilized by di-(o-tolyl) fumarate that converts the stable pre-catalyst form into a catalytically active species. Computational evaluation provided evidence against a simple ligand exchange as the activation mechanism, and a stoichiometric activation process that covalently modifies the stabilizing ligand was identified. A detailed computational picture for the activation process was developed, with predictive insights that explain the catalyst features that lead to both active and inactive precatalysts.

Growth of Catalytically Active Nanostructures in the Nonequilibrium Epitaxy Regime

2015 ◽  
Vol 60 (6) ◽  
pp. 546-552
Author(s):  
V.M. Gorshkov ◽  
◽  
V.V. Kuzmenko
Keyword(s):  
Catalytically Active
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