Kinetic study of isospecific active sites formed by various alkylaluminiums on MgCl2-supported Ziegler catalyst at the initial stage of propene polymerization

1997 ◽  
Vol 198 (4) ◽  
pp. 1249-1255 ◽  
Author(s):  
Hideharu Mori ◽  
Hiromitsu Iguchi ◽  
Kouichi Hasebe ◽  
Minoru Terano
Keyword(s):  
Kinetic Study ◽  
Active Sites ◽  
Initial Stage ◽  
Propene Polymerization

New Evidence on the Nature of the Active Sites in Heterogeneous Ziegler−Natta Catalysts for Propene Polymerization

1997 ◽  
Vol 30 (16) ◽  
pp. 4786-4790 ◽  
Author(s):  
Vincenzo Busico ◽  
Roberta Cipullo ◽  
Giovanni Talarico ◽  
Anna Laura Segre ◽  
John C. Chadwick
Keyword(s):  
Active Sites ◽  
Propene Polymerization ◽  
New Evidence ◽  
Ziegler Natta Catalysts

scholarly journals Sequential Immobilization of Ansa-Hafnocene Complexes for Propene Polymerization

2019 ◽  
Author(s):  
Marius Arz ◽  
Tim Kratky ◽  
Sebastian Günther ◽  
Katia Rodewald ◽  
Thomas Burger ◽  
...  
Keyword(s):  
Active Sites ◽  
Poor Performance ◽  
Reaction Conditions ◽  
Continuous Polymerization ◽  
Propene Polymerization ◽  
Close Proximity ◽  
Catalytically Active

We report the immobilization of the ultrarigid <i>ansa</i>-hafnocene complexes [Me<sub>2</sub>Si(Ind*)<sub>2</sub>HfCl<sub>2</sub>] (Ind* = 7,(3',5'-Di-<i>tert</i>-butylphenyl)-4-methoxy-2-methylindenyl) on silica as heteregeneous catalysts for propene polymerization. A sequential three-step synthesis on the siliceous surface led to pre-catalysts of the generalized structure SiO<sub>2</sub>-Si(Ind*)<sub>2</sub>HfCl<sub>2</sub>, which possess the silylene bridge of the substituted bis(indenyl) ligand directly attached to the surface. The immobilized pre-catalysts show very poor performance in the polymerization of propene, independent on the reaction conditions and the employed silica. Based on the results, we suggest that the close proximity of the catalyst to the surface combined with the steric congestion provoked by the ligand prevents a continuous polymerization, most likely due to a blockage of the catalytically active sites with growing polymer.<br>

scholarly journals Exploring the Mechanism of Olfactory Recognition at the Initial Stage by Modeling the Emission Spectrum of Electron Transfer

2019 ◽  
Author(s):  
Shu Liu ◽  
Rao Fu ◽  
Guangwu Li
Keyword(s):  
Electron Transfer ◽  
Emission Spectrum ◽  
Active Sites ◽  
Isotope Effects ◽  
Emission Spectra ◽  
Initial Stage ◽  
Olfactory Sense ◽  
Bitter Almond ◽  
Deuterated Analogue ◽  
Odorant Molecule

AbstractOlfactory sense remains elusive regarding the primary reception mechanism. Some studies suggest that olfaction is a spectral sense, the olfactory event is triggered by electron transfer (ET) across the odorants at the active sites of odorant receptors (ORs). Herein we present a Donor-Bridge-Acceptor model, proposing that the ET process can be viewed as an electron hopping from the donor molecule to the odorant molecule (Bridge), then hopping off to the acceptor molecule, making the electronic state of the odorant molecule change along with vibrations (vibronic transition). The odorant specific parameter, Huang–Rhys factor can be derived from ab initio calculations, which make the simulation of ET spectra achievable. In this study, we revealed that the emission spectra (after Gaussian convolution) can be acted as odor characteristic spectra. Using the emission spectrum of ET, we were able to reasonably interpret the similar bitter-almond odors among hydrogen cyanide, benzaldehyde and nitrobenzene. In terms of isotope effects, we succeeded in explaining why subjects can easily distinguish cyclopentadecanone from its fully deuterated analogue cyclopentadecanone-d28 but not distinguishing acetophenone from acetophenone-d8.

Kinetic study on the initial stage of the fibrinogen-fibrin conversion by turbidimetry

1981 ◽  
Vol 259 (12) ◽  
pp. 1246-1248 ◽  
Author(s):  
H. Sato ◽  
E. Nakanishi ◽  
A. Nakajima
Keyword(s):  
Kinetic Study ◽  
Initial Stage
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