An investigation on the role of Re as a promoter in Ag Cs Re/α-Al 2 O 3 high-selectivity, ethylene epoxidation catalysts

2015 ◽  
Vol 322 ◽  
pp. 14-23 ◽  
Author(s):  
Weijian Diao ◽  
Christopher D. DiGiulio ◽  
Melanie T. Schaal ◽  
Shuguo Ma ◽  
John R. Monnier
Keyword(s):  
High Selectivity ◽  
Ethylene Epoxidation

scholarly journals Multivalent weak interactions enhance selectivity of interparticle binding

2020 ◽  
Vol 117 (37) ◽  
pp. 22690-22697 ◽  
Author(s):  
M. R. W. Scheepers ◽  
L. J. van IJzendoorn ◽  
M. W. J. Prins
Keyword(s):  
Targeted Drug Delivery ◽  
Colloidal Particles ◽  
High Selectivity ◽  
Weak Interactions ◽  
Theoretical Work ◽  
Coated Particles ◽  
Receptor Interactions ◽  
Two Factors ◽  
Experimental Findings

Targeted drug delivery critically depends on the binding selectivity of cargo-transporting colloidal particles. Extensive theoretical work has shown that two factors are necessary to achieve high selectivity for a threshold receptor density: multivalency and weak interactions. Here, we study a model system of DNA-coated particles with multivalent and weak interactions that mimics ligand–receptor interactions between particles and cells. Using an optomagnetic cluster experiment, particle aggregation rates are measured as a function of ligand and receptor densities. The measured aggregation rates show that the binding becomes more selective for shorter DNA ligand–receptor pairs, proving that multivalent weak interactions lead to enhanced selectivity in interparticle binding. Simulations confirm the experimental findings and show the role of ligand–receptor dissociation in the selectivity of the weak multivalent binding.

scholarly journals Evidence that Ca2+-release-activated Ca2+ channels in rat hepatocytes are required for the maintenance of hormone-induced Ca2+ oscillations

2003 ◽  
Vol 370 (2) ◽  
pp. 695-702 ◽  
Author(s):  
Roland B. GREGORY ◽  
Gregory J. BARRITT
Keyword(s):  
High Selectivity ◽  
Rat Hepatocytes ◽  
Isolated Hepatocytes ◽  
Cation Channels ◽  
Isolated Rat Hepatocytes ◽  
Pharmacological Agents ◽  
Crac Channels ◽  
Kinetics Of ◽  
Ca2 Channels

Store-operated Ca2+ channels in liver cells have been shown previously to exhibit a high selectivity for Ca2+ and to have properties indistinguishable from those of Ca2+-release-activated Ca2+ (CRAC) channels in mast cells and lymphocytes [Rychkov, Brereton, Harland and Barritt (2001) Hepatology 33, 938—947]. The role of CRAC channels in the maintenance of hormone-induced oscillations in the cytoplasmic free Ca2+ concentration ([Ca2+]cyt) in isolated rat hepatocytes was investigated using several inhibitors of CRAC channels. 2-Aminoethyl diphenylborate (2-APB; 75μM), Gd3+ (1μM) and 1-{β-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl}-1H-imidazole hydrochloride (SK&F 96365; 50μM) each inhibited vasopressin- and adrenaline (epinephrine)-induced Ca2+ oscillations (measured using fura-2). The characteristics of this inhibition were similar to those of inhibition caused by decreasing the extracellular Ca2+ concentration to zero by addition of EGTA. The effect of 2-APB was reversible. In contrast, LOE-908 {(R,S)-(3,4-dihydro-6,7-dimethoxy-isochinolin-1-yl)-2-phenyl-N,N-di[2-(2,3,4-trimethoxyphenyl)ethyl]acetamidemesylate}(30μM), used commonly to block Ca2+ inflow through intracellular-messenger-activated, non-selective cation channels, did not inhibit the Ca2+ oscillations. In the absence of added extracellular Ca2+, 2-APB, Gd3+ and SK&F 96365 did not alter the kinetics of the increase in [Ca2+]cyt induced by a concentration of adrenaline or vasopressin that induces continuous Ca2+ oscillations at the physiological extracellular Ca2+ concentration. Ca2+ inflow through non-selective cation channels activated by maitotoxin could not restore Ca2+ oscillations in cells treated with 2-APB to block Ca2+ inflow through CRAC channels. Evidence for the specificity of the pharmacological agents for inhibition of CRAC channels under the conditions of the present experiments with hepatocytes is discussed. It is concluded that Ca2+ inflow through CRAC channels is required for the maintenance of hormone-induced Ca2+ oscillations in isolated hepatocytes.

scholarly journals Cyclic(Alkyl)(Amino)Carbene Ligands Enable Cu-Catalyzed Markovnikov Protoboration and Protosilylation of Terminal Alkynes: A Versatile Portal to Functionalized Alkenes

2021 ◽  
Author(s):  
Yang Gao ◽  
Sima Yazdani ◽  
Aaron Kendrick ◽  
Glen Junor ◽  
Douglas Grotjahn ◽  
...  
Keyword(s):  
High Selectivity ◽  
Building Blocks ◽  
Terminal Alkynes ◽  
Carbene Ligands ◽  
Catalytic Systems ◽  
General Solutions ◽  
Shed Light ◽  
Limited Scope

Regioselective hydrofunctionalization of alkynes represents a straightforward route to access alkenyl boronate and silane building blocks. In previously reported catalytic systems, high selectivity is achieved with a limited scope of substrates and/or reagents, with general solutions lacking. Herein, we describe a selective copper-catalyzed Markovnikov hydrofunctionalization of terminal alkynes that is facilitated by strongly donating cyclic (alkyl)(amino)carbene (CAAC) ligands. Using this method, both alkyl- and aryl-substituted alkynes are coupled with a variety of boryl and silyl reagents with high α-selectivity. The reaction is scalable, and the products are versatile intermediates that can participate in various downstream transformations. Preliminary mechanistic experiments shed light on the role of CAAC ligands in this process.

scholarly journals Niobium on BEA Dealuminated Zeolite for High Selectivity Dehydration Reactions of Ethanol and Xylose into Diethyl Ether and Furfural

Nanomaterials ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 1269
Author(s):  
Deborah S. Valadares ◽  
Maria Clara H. Clemente ◽  
Elon F. de Freitas ◽  
Gesley Alex V. Martins ◽  
José A. Dias ◽  
...  
Keyword(s):  
Solid State ◽  
Diethyl Ether ◽  
High Selectivity ◽  
Catalytic Properties ◽  
Good Activity ◽  
Green Solvent ◽  
Turnover Number ◽  
Dehydration Reactions ◽  
Leveling Effect

In this work, we investigated the role of solid-state dealumination by (NH4)2SiF6 (25% Al removal and 13% Si insertion), the impregnation of niobium (10, 18, and 25 wt. %) on dealuminated *BEA (DB) zeolite and their catalytic properties in ethanol and xylose transformations. Among all the studied catalysts, 18%Nb-DB showed increased mesoporosity and external areas. A leveling effect in the number and strength of the proposed two sites (Brønsted and Lewis) present in the catalyst (n1 = 0.24 mmol g−1, −ΔH1 = 49 kJ mol−1, and n2 = 0.20 mmol g−1, –ΔH2 = 42 kJ mol−1) in the catalyst 18%Nb-DB, might be responsible for its good activity. This catalyst presented the highest selectivity for diethyl ether, DEE (97%) with 61% conversion after 50 ethanol pulses at 230 °C (turnover number, TON DEE = 1.15). These features allowed catalytically fruitful bonding of the ethanol molecules to the neighboring sites on the channels, facilitating bimolecular ether formation through a possible SN2 mechanism. The same catalyst was active and selective for transformation of xylose at 180 °C, showing 64% conversion and 51% selectivity for furfural (TON Furfural = 24.7) using water as a green solvent.

BJ-48, a novel thrombin-like enzyme from the Bothrops jararacussu venom with high selectivity for Arg over Lys in P1: Role of N-glycosylation in thermostability and active site accessibility

Toxicon ◽  
2007 ◽  
Vol 50 (1) ◽  
pp. 18-31 ◽  
Author(s):  
Floriano P. Silva-Junior ◽  
Herbert L.M. Guedes ◽  
Laura C. Garvey ◽  
Aniesse S. Aguiar ◽  
Saulo C. Bourguignon ◽  
...  
Keyword(s):  
Active Site ◽  
High Selectivity ◽  
Bothrops Jararacussu

The role of the support in achieving high selectivity in the direct formation of hydrogen peroxide

2008 ◽  
Vol 10 (11) ◽  
pp. 1162 ◽  
Author(s):  
Edwin Ntainjua N. ◽  
Jennifer K. Edwards ◽  
Albert F. Carley ◽  
Jose Antonio Lopez-Sanchez ◽  
Jacob A. Moulijn ◽  
...  
Keyword(s):  
Hydrogen Peroxide ◽  
High Selectivity ◽  
Direct Formation

Antigen-Induced Eosinophilic Lung Inflammation Develops in Mice Deficient in Chemokine Eotaxin

Blood ◽  
1998 ◽  
Vol 92 (10) ◽  
pp. 3912-3923 ◽  
Author(s):  
Yi Yang ◽  
James Loy ◽  
Rolf-Peter Ryseck ◽  
Daniel Carrasco ◽  
Rodrigo Bravo
Keyword(s):  
Endothelial Cells ◽  
Inflammatory Response ◽  
Lung Inflammation ◽  
Immunohistochemical Staining ◽  
High Selectivity ◽  
Allergic Diseases ◽  
Mutant Mice ◽  
Cc Chemokine ◽  
Lung Eosinophilia

Abstract The mechanisms that regulate the selective infiltration of eosinophils in certain allergic diseases are still poorly understood. The CC chemokine eotaxin is a potent chemoattractant, highly specific for eosinophils. Recent studies have implicated that eotaxin plays an important role in the recruitment of eosinophils in different inflammation processes. A number of other chemokines, cytokines, and chemoattractants also have chemotactic activities for eosinophils and some of them present high selectivity for eosinophils. To further study the role of eotaxin in inflammation, we generated mutant mice with the eotaxin gene disrupted and replaced by the Escherichia coliβ-galactosidase gene. These mice developed normally and had no histologic or hematopoietic abnormalities. Furthermore, our studies showed that the lack of eotaxin did not affect the recruitment of eosinophils in the inflammation models induced by Sephadex beads and thioglycollate, as well as in an experimental lung eosinophilia model induced by ovalbumin aerosol challenge, even at the onset of the inflammatory response. The replacement of the eotaxin gene by the β-galactosidase gene provided a useful marker to monitor the activity of the eotaxin promoter under normal conditions and after antigen challenges. Immunohistochemical staining suggested that endothelial cells were the major sources of eotaxin expression.

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