scholarly journals A New Insight into the Comonomer Effect through NMR Analysis in Metallocene Catalysed Propene–co–1-Nonene Copolymers

Polymers ◽  
2019 ◽  
Vol 11 (8) ◽  
pp. 1266
Author(s):  
Qiong Wu ◽  
Alberto García-Peñas ◽  
Rosa Barranco-García ◽  
María Luisa Cerrada ◽  
Rosario Benavente ◽  
...  
Keyword(s):  
Active Sites ◽  
Nmr Analysis ◽  
Reaction Parameters ◽  
Transfer Processes ◽  
Detailed Explanation ◽  
Selective Interaction ◽  
End Groups ◽  
Alpha Olefin ◽  
Kinetic Phenomenon ◽  
Insight Into

The “comonomer effect” is an intriguing kinetic phenomenon in olefin copolymerization that still remains without a detailed explanation. It typically relates to the rate of enhancement undergone in ethylene and propene catalytic polymerization just by adding small fractions of an alpha-olefin. The difficulty lies in the fact that changes caused by the presence of the comonomer in reaction parameters are so conspicuous that it is really difficult to pin down which of them is the primary cause and which ones are side factors with marginal contribution to the phenomenon. Recent investigations point to the modification of the catalyst active sites as the main driving factor. In this work, the comonomer effect in the metallocene copolymerization of propene and 1-nonene is analysed and correlated to the comonomer role in the termination of the chain-growing process. The associated termination mechanisms involved furnish most of chain-free active sites, in which the selective interaction of the comonomer was proposed to trigger the insertion of monomers. A thorough characterisation of chain-end groups by means of the 1H NMR technique allows for detailing of specific transfer processes, ascribed to comonomer insertions, as well as evidencing the influence of the growing chain’s microstructure over the different termination processes available.

scholarly journals Insight into Inhibitor Binding in the Eukaryotic Proteasome: Computations of the 20S CP

2018 ◽  
Vol 19 (12) ◽  
pp. 3858
Author(s):  
Milan Hodošček ◽  
Nadia Elghobashi-Meinhardt
Keyword(s):  
Electrostatic Interactions ◽  
Active Sites ◽  
Sampling Period ◽  
Md Simulations ◽  
Structural Features ◽  
Relaxation Dynamics ◽  
Inhibitor Binding ◽  
Computational Analyses ◽  
Insight Into ◽  
Proteolytic Chamber

A combination of molecular dynamics (MD) simulations and computational analyses uncovers structural features that may influence substrate passage and exposure to the active sites within the proteolytic chamber of the 20S proteasome core particle (CP). MD simulations of the CP reveal relaxation dynamics in which the CP slowly contracts over the 54 ns sampling period. MD simulations of the SyringolinA (SylA) inhibitor within the proteolytic B 1 ring chamber of the CP indicate that favorable van der Waals and electrostatic interactions account for the predominant association of the inhibitor with the walls of the proteolytic chamber. The time scale required for the inhibitor to travel from the center of the proteolytic chamber to the chamber wall is on the order of 4 ns, accompanied by an average energetic stabilization of approximately −20 kcal/mol.

scholarly journals Kinetics of Selective Catalytic Reduction of Nitric Oxide over Pt-Cu-Zsm5 Catalyst

1970 ◽  
Vol 4 (1) ◽  
Author(s):  
Ismail Mohd Saaid ◽  
Abdul Rahman Mohamed and Subhash Bhatia
Keyword(s):  
Nitric Oxide ◽  
Selective Catalytic Reduction ◽  
Active Sites ◽  
No Reduction ◽  
Bimetallic Catalyst ◽  
Catalytic Reduction ◽  
Covalent Bond ◽  
Reaction Parameters ◽  
Heterogeneous Model ◽  
Kinetics Of

Kinetics for the selective catalytic reduction (SCR) of nitric oxide (NO) using i-C4H10 as the reducing agent over Pt-Cu-ZSM5 has been investigated in the temperature range of 200 ?C – 450 oC. Langmuir-Hinshelwood-Hougen-Watson model was proposed for kinetics of the reaction and reaction parameters were evaluated.  The heat of adsorption of NO was found to be considerably high, attributed to strong covalent bond between NO gas molecules and metal active sites.  Using reaction parameters obtained from the experiment, the heterogeneous model could form a good correlation between experimental and simulated values of NO reduction. Key Words: Reaction kinetics, Selective catalytic reduction, NO reduction, Bimetallic catalyst, H-ZSM-5 zeolite.

scholarly journals Electrochemically Induced In-Situ Generated Co(OH)2 Nanoplates to Promote the Volmer Process Toward Efficient Alkaline Hydrogen Evolution Reaction

2020 ◽  
Author(s):  
Hong Liu ◽  
Jian-Jun Wang ◽  
Li-Wen Jiang ◽  
Yuan Huang ◽  
Bing Bing Chen ◽  
...  
Keyword(s):  
Hydrogen Evolution ◽  
Hydrogen Evolution Reaction ◽  
Active Sites ◽  
Water Electrolysis ◽  
Water Dissociation ◽  
Alkaline Water Electrolysis ◽  
Additional Water ◽  
Dissociation Step ◽  
Insight Into

<p>Hydrogen production via alkaline water electrolysis is of significant interest. However, the additional water dissociation step makes the Volmer step a relatively more sluggish kinetics and consequently leads to a slower reaction rate than that in acidic solution. Herein, we demonstrate an effective strategy that Co(OH)<sub>2</sub> can promote the Volmer process by accelerating water dissociation and enhance the electrocatalytic performance of CoP toward alkaline hydrogen evolution reaction. The Co(OH)<sub>2</sub> nanoplates are electrochemically induced in-situ generated to form a nanotree-like structure with porous CoP nanowires, endowing the hybrid electrocatalyst with superior charge transportation, more exposed active sites, and enhanced reaction kinetics. This strategy may be extended to <a></a><a>other phosphides and chalcogenides </a>and provide insight into the design and fabrication of efficient alkaline HER catalysts.</p>

NMR Analysis of Polyester Urethane End Groups and Solid-Phase Hydrolysis Kinetics

2000 ◽  
Vol 33 (10) ◽  
pp. 3569-3576 ◽  
Author(s):  
David M. LeMaster ◽  
Griselda Hernández
Keyword(s):  
Solid Phase ◽  
Hydrolysis Kinetics ◽  
Nmr Analysis ◽  
Polyester Urethane ◽  
End Groups

scholarly journals Electrochemical insights into the mechanism of NiFe membrane-bound hydrogenases

2016 ◽  
Vol 44 (1) ◽  
pp. 315-328 ◽  
Author(s):  
Lindsey A. Flanagan ◽  
Alison Parkin
Keyword(s):  
Active Site ◽  
Precious Metal ◽  
Active Sites ◽  
Review Paper ◽  
Spectroscopic Studies ◽  
Electrochemical Studies ◽  
Control Centre ◽  
Catalytic Active Sites ◽  
Membrane Bound ◽  
Insight Into

Hydrogenases are enzymes of great biotechnological relevance because they catalyse the interconversion of H2, water (protons) and electricity using non-precious metal catalytic active sites. Electrochemical studies into the reactivity of NiFe membrane-bound hydrogenases (MBH) have provided a particularly detailed insight into the reactivity and mechanism of this group of enzymes. Significantly, the control centre for enabling O2 tolerance has been revealed as the electron-transfer relay of FeS clusters, rather than the NiFe bimetallic active site. The present review paper will discuss how electrochemistry results have complemented those obtained from structural and spectroscopic studies, to present a complete picture of our current understanding of NiFe MBH.

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