Benzene Radical Cation Formation on Hydrogen Mordenite. The Role of Adsorbed Oxygen

1972 ◽  
Vol 50 (13) ◽  
pp. 2041-2046 ◽  
Author(s):  
N. H. Sagert ◽  
R. M. L. Pouteau ◽  
M. G. Bailey ◽  
F. P. Sargent
Keyword(s):  
Cation Radical ◽  
Radical Cations ◽  
Acid Sites ◽  
Excess Oxygen ◽  
Oxygen Treatment ◽  
Chemisorbed Oxygen ◽  
Water Of Hydration ◽  
Initial Spectrum ◽  
A Site

The e.p.r. spectrum of benzene on hydrogen mordenite (Zeolon H) has been studied as a function of coverage, degassing temperature, and hydrogen and oxygen treatment. The initial spectrum observed was that due to the benzene cation radical dimer. The maximum number of spins was formed when the solid was completely saturated with benzene. Large yields were obtained only when the zeolitic water and water of hydration of the protons were removed. The largest yields were observed where significant dehydroxylation had occurred. Chemisorbed oxygen was essential, and there was a 1:1.2 ratio between the maximum number of spins observed in the presence of excess oxygen and the amount of oxygen chemisorbed. The largest concentration of radical cations noted (2 × 1018/g) was much smaller than the number of acid sites known to be present (1021/g). In fact, only one unit cell of the hydrogen mordenite in 100 had a site capable of oxidizing benzene to the cation. Hence these sites must be in special positions in the solid.

The Return of Alsace to France, 1918-1939

2018 ◽  
Author(s):  
Alison Carrol
Keyword(s):  
National Policy ◽  
Third Republic ◽  
French Society ◽  
German Empire ◽  
Cross Border ◽  
The First World War ◽  
German Speaking ◽  
A Site ◽  
First World

In 1918 the end of the First World War triggered the return of Alsace to France after almost fifty years of annexation into the German Empire. Enthusiastic crowds in Paris and Alsace celebrated the homecoming of the so-called lost province, but return proved far less straightforward than anticipated. The region’s German-speaking population demonstrated strong commitment to local cultures and institutions, as well as their own visions of return to France. As a result, the following two decades saw politicians, administrators, industrialists, cultural elites, and others grapple with the question of how to make Alsace French again. The answer did not prove straightforward; differences of opinion emerged both inside and outside the region, and reintegration became a fiercely contested process that remained incomplete when war broke out in 1939. The Return of Alsace to France examines this story. Drawing upon national, regional, and local archives, it follows the difficult process of Alsace’s reintegration into French society, culture, political and economic systems, and legislative and administrative institutions. It connects the microhistory of the region with the macro levels of national policy, international relations, and transnational networks, and with the cross-border flows of ideas, goods, people, and cultural products that shaped daily life in Alsace. Revealing Alsace to be a site of exchange between a range of interest groups with different visions of the region’s future, this book underlines the role of regional populations and cross-border interactions in forging the French Third Republic.

RNA secondary structure dependence in METTL3–METTL14 mRNA methylation is modulated by the N-terminal domain of METTL3

2020 ◽  
Vol 402 (1) ◽  
pp. 89-98
Author(s):  
Nathalie Meiser ◽  
Nicole Mench ◽  
Martin Hengesbach
Keyword(s):  
Secondary Structure ◽  
Rna Binding ◽  
Specific Protein ◽  
Structure Dependence ◽  
Terminal Domain ◽  
Methylation Assay ◽  
A Site ◽  
Methylation Activity

AbstractN6-methyladenosine (m6A) is the most abundant modification in mRNA. The core of the human N6-methyltransferase complex (MTC) is formed by a heterodimer consisting of METTL3 and METTL14, which specifically catalyzes m6A formation within an RRACH sequence context. Using recombinant proteins in a site-specific methylation assay that allows determination of quantitative methylation yields, our results show that this complex methylates its target RNAs not only sequence but also secondary structure dependent. Furthermore, we demonstrate the role of specific protein domains on both RNA binding and substrate turnover, focusing on postulated RNA binding elements. Our results show that one zinc finger motif within the complex is sufficient to bind RNA, however, both zinc fingers are required for methylation activity. We show that the N-terminal domain of METTL3 alters the secondary structure dependence of methylation yields. Our results demonstrate that a cooperative effect of all RNA-binding elements in the METTL3–METTL14 complex is required for efficient catalysis, and that binding of further proteins affecting the NTD of METTL3 may regulate substrate specificity.

scholarly journals The RelA hydrolase domain acts as a molecular switch for (p)ppGpp synthesis

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Anurag Kumar Sinha ◽  
Kristoffer Skovbo Winther
Keyword(s):  
Active Sites ◽  
Molecular Switch ◽  
Cell Physiology ◽  
Synthetase Activity ◽  
Wild Type ◽  
Functional Studies ◽  
Loop Region ◽  
A Site ◽  
Trna Binding

AbstractBacteria synthesize guanosine tetra- and penta phosphate (commonly referred to as (p)ppGpp) in response to environmental stresses. (p)ppGpp reprograms cell physiology and is essential for stress survival, virulence and antibiotic tolerance. Proteins of the RSH superfamily (RelA/SpoT Homologues) are ubiquitously distributed and hydrolyze or synthesize (p)ppGpp. Structural studies have suggested that the shift between hydrolysis and synthesis is governed by conformational antagonism between the two active sites in RSHs. RelA proteins of γ-proteobacteria exclusively synthesize (p)ppGpp and encode an inactive pseudo-hydrolase domain. Escherichia coli RelA synthesizes (p)ppGpp in response to amino acid starvation with cognate uncharged tRNA at the ribosomal A-site, however, mechanistic details to the regulation of the enzymatic activity remain elusive. Here, we show a role of the enzymatically inactive hydrolase domain in modulating the activity of the synthetase domain of RelA. Using mutagenesis screening and functional studies, we identify a loop region (residues 114–130) in the hydrolase domain, which controls the synthetase activity. We show that a synthetase-inactive loop mutant of RelA is not affected for tRNA binding, but binds the ribosome less efficiently than wild type RelA. Our data support the model that the hydrolase domain acts as a molecular switch to regulate the synthetase activity.

scholarly journals On the Role of Protonic Acid Sites in Cu Loaded FAU31 Zeolite as a Catalyst for the Catalytic Transformation of Furfural to Furan

Molecules ◽  
2021 ◽  
Vol 26 (7) ◽  
pp. 2015
Author(s):  
Łukasz Kuterasiński ◽  
Małgorzata Smoliło-Utrata ◽  
Joanna Kaim ◽  
Wojciech Rojek ◽  
Jerzy Podobiński ◽  
...  
Keyword(s):  
Active Sites ◽  
Acid Sites ◽  
Bronsted Acid ◽  
Brønsted Acid ◽  
Brønsted Acid Sites ◽  
Protonic Acid ◽  
Brönsted Acid ◽  
Brönsted Acid Sites ◽  
Bronsted Acid Sites

The aim of the present paper is to study the speciation and the role of different active site types (copper species and Brønsted acid sites) in the direct synthesis of furan from furfural catalyzed by copper-exchanged FAU31 zeolite. Four series of samples were prepared by using different conditions of post-synthesis treatment, which exhibit none, one or two types of active sites. The catalysts were characterized by XRD, low-temperature sorption of nitrogen, SEM, H2-TPR, NMR and by means of IR spectroscopy with ammonia and CO sorption as probe molecules to assess the types of active sites. All catalyst underwent catalytic tests. The performed experiments allowed to propose the relation between the kind of active centers (Cu or Brønsted acid sites) and the type of detected products (2-metylfuran and furan) obtained in the studied reaction. It was found that the production of 2-methylfuran (in trace amounts) is determined by the presence of the redox-type centers, while the protonic acid sites are mainly responsible for the furan production and catalytic activity in the whole temperature range. All studied catalysts revealed very high susceptibility to coking due to polymerization of furfural.

scholarly journals A MODEL OF CREATIVE HERITAGE FOR INDUSTRY: DESIGNING NEW RULES WHILE PRESERVING THE PRESENT SYSTEM OF RULES

2021 ◽  
Vol 1 ◽  
pp. 141-150
Author(s):  
Honorine Harlé ◽  
Pascal Le Masson ◽  
Benoit Weil
Keyword(s):  
Case Studies ◽  
Design Process ◽  
Industry 4.0 ◽  
Innovation Management ◽  
Present System ◽  
Innovative Capability ◽  
Current Change ◽  
A Site ◽  
Do So

AbstractIn industry, there is at once a strong need for innovation and a need to preserve the existing system of production. Thus, although the literature insists on the necessity of the current change toward Industry 4.0, how to implement it remains problematic because the preservation of the factory is at stake. Moreover, the question of the evolution of the system depends on its innovative capability, but it is difficult to understand how a new rule can be designed and implemented in a factory. This tension between preservation and innovation is often explained in the literature as a process of creative destruction. Looking at the problem from another perspective, this article models the factory as a site of creative heritage, enabling creation within tradition, i.e., creating new rules while preserving the system of rules. Two case studies are presented to illustrate the model. The paper shows that design in the factory relies on the ability to validate solutions. To do so, the design process can explore and give new meaning to the existing rules. The role of innovation management is to choose the degree of revision of the rules and to make it possible.

scholarly journals Role of CO2 During Oxidative Dehydrogenation of Propane Over Bulk and Activated-Carbon Supported Cerium and Vanadium Based Catalysts

2021 ◽  
Author(s):  
Petar Djinović ◽  
Janez Zavašnik ◽  
Janvit Teržan ◽  
Ivan Jerman
Keyword(s):  
Catalytic Activity ◽  
Activated Carbon ◽  
Oxidative Dehydrogenation ◽  
Active Phase ◽  
Lattice Oxygen ◽  
Chemisorbed Oxygen ◽  
Catalytically Active ◽  
Temperature Programmed ◽  
Propane Cracking

AbstractCeO2, V2O5 and CeVO4 were synthesised as bulk oxides, or deposited over activated carbon, characterized by XRD, HRTEM, CO2-TPO, C3H8-TPR, DRIFTS and Raman techniques and tested in propane oxidative dehydrogenation using CO2. Complete oxidation of propane to CO and CO2 is favoured by lattice oxygen of CeO2. The temperature programmed experiments show the ~ 4 nm AC supported CeO2 crystallites become more susceptible to reduction by propane, but less prone to re-oxidation with CO2 compared to bulk CeO2. Catalytic activity of CeVO4/AC catalysts requires a 1–2 nm amorphous CeVO4 layer. During reaction, the amorphous CeVO4 layer crystallises and several atomic layers of carbon cover the CeVO4 surface, resulting in deactivation. During reaction, V2O5 is irreversibly reduced to V2O3. The lattice oxygen in bulk V2O5 favours catalytic activity and propene selectivity. Bulk V2O3 promotes only propane cracking with no propene selectivity. In VOx/AC materials, vanadium carbide is the catalytically active phase. Propane dehydrogenation over VC proceeds via chemisorbed oxygen species originating from the dissociated CO2. Graphic Abstract

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