Sequential Immobilization of Ansa-Hafnocene Complexes for Propene Polymerization

10.26434/chemrxiv.10028348.v1 ◽

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 ansa-hafnocene complexes [Me2Si(Ind*)2HfCl2] (Ind* = 7,(3',5'-Di-tert-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 SiO2-Si(Ind*)2HfCl2, 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.

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Manganese vacancy-confined single-atom Ag in cryptomelane nanorods for efficient Wacker oxidation of styrene derivatives

Chemical Science ◽

10.1039/d1sc00700a ◽

2021 ◽

Author(s):

Hongling Yang ◽

Xun Zhang ◽

Yi Yu ◽

Zheng Chen ◽

Qinggang Liu ◽

...

Keyword(s):

Molecular Sieve ◽

Active Sites ◽

Single Atom ◽

Wacker Oxidation ◽

Catalytically Active ◽

Styrene Derivatives

Single-atom catalysts provide a pathway to elucidate the nature of catalytically active sites. However, keeping them stabilized during operation proves to be challenging. Herein, we employ cryptomelane-type octahedral molecular sieve...

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Regulating the Catalytically Active Sites in Low-Cost and Earth-Abundant 3d Transition-Metal-Based Electrode Materials for High-Performance Zinc–Air Batteries

Energy & Fuels ◽

10.1021/acs.energyfuels.1c00388 ◽

2021 ◽

Vol 35 (8) ◽

pp. 6483-6503

Author(s):

Jiajun Wang ◽

Hui Hu ◽

Hong Zhang ◽

Jun Zhao ◽

Xiaopeng Li ◽

...

Keyword(s):

Transition Metal ◽

Active Sites ◽

High Performance ◽

Electrode Materials ◽

Low Cost ◽

Catalytically Active ◽

Earth Abundant ◽

Zinc Air Batteries

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Diffuse Reflectance FT-IR Characterization of Active Sites under Reaction Conditions: The Production of Oxygenates in the CO/H2 Reaction

Applied Spectroscopy ◽

10.1366/0003702944027345 ◽

1994 ◽

Vol 48 (10) ◽

pp. 1208-1212 ◽

Cited By ~ 7

Author(s):

J. J. Benítez ◽

I. Carrizosa ◽

J. A. Odriozola

Keyword(s):

Infrared Spectra ◽

Active Sites ◽

Diffuse Reflectance ◽

Reaction Conditions ◽

In Situ Drifts ◽

Ft Ir

The reactivity of a Lu2O3-promoted Rh/Al2O3 catalyst in the CO/H2 reaction is reported. Methane, heavier hydrocarbons, methanol, and ethanol are obtained. In situ DRIFTS has been employed to record the infrared spectra under the actual reaction conditions. The structure of the observed COads DRIFTS bands has been resolved into its components. The production of oxygenates (methanol and ethanol) has been correlated with the results of the deconvolution calculation. Specific sites for the production of methanol and ethanol in the CO/H2 reaction over a Rh,Lu2O3/Al2O3 catalyst are proposed.

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Tuning electronic states of catalytic sites enhances SCR activity of hexagonal WO3by Mo framework substitution

Catalysis Science & Technology ◽

10.1039/c7cy00416h ◽

2017 ◽

Vol 7 (12) ◽

pp. 2467-2473 ◽

Cited By ~ 4

Author(s):

Yaxin Chen ◽

Zichenxi Dong ◽

Zhiwei Huang ◽

Meijuan Zhou ◽

Jiayi Gao ◽

...

Keyword(s):

Active Sites ◽

Electronic States ◽

Catalytic Sites ◽

Catalytically Active

The electronic states of the catalytically active sites of HWO were tuned by Mo framework substitution.

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Role of a ribosomal RNA phosphate oxygen during the EF-G–triggered GTP hydrolysis

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1505231112 ◽

2015 ◽

Vol 112 (20) ◽

pp. E2561-E2568 ◽

Cited By ~ 20

Author(s):

Miriam Koch ◽

Sara Flür ◽

Christoph Kreutz ◽

Eric Ennifar ◽

Ronald Micura ◽

...

Keyword(s):

Ribosomal Rna ◽

Electrostatic Interactions ◽

Elongation Factor ◽

Direct Interaction ◽

Phosphate Group ◽

Gtp Hydrolysis ◽

Elongation Cycle ◽

Close Proximity ◽

Catalytically Active ◽

Gtpase Activation

Elongation factor-catalyzed GTP hydrolysis is a key reaction during the ribosomal elongation cycle. Recent crystal structures of G proteins, such as elongation factor G (EF-G) bound to the ribosome, as well as many biochemical studies, provide evidence that the direct interaction of translational GTPases (trGTPases) with the sarcin-ricin loop (SRL) of ribosomal RNA (rRNA) is pivotal for hydrolysis. However, the precise mechanism remains elusive and is intensively debated. Based on the close proximity of the phosphate oxygen of A2662 of the SRL to the supposedly catalytic histidine of EF-G (His87), we probed this interaction by an atomic mutagenesis approach. We individually replaced either of the two nonbridging phosphate oxygens at A2662 with a methyl group by the introduction of a methylphosphonate instead of the natural phosphate in fully functional, reconstituted bacterial ribosomes. Our major finding was that only one of the two resulting diastereomers, the SP methylphosphonate, was compatible with efficient GTPase activation on EF-G. The same trend was observed for a second trGTPase, namely EF4 (LepA). In addition, we provide evidence that the negative charge of the A2662 phosphate group must be retained for uncompromised activity in GTP hydrolysis. In summary, our data strongly corroborate that the nonbridging proSP phosphate oxygen at the A2662 of the SRL is critically involved in the activation of GTP hydrolysis. A mechanistic scenario is supported in which positioning of the catalytically active, protonated His87 through electrostatic interactions with the A2662 phosphate group and H-bond networks are key features of ribosome-triggered activation of trGTPases.

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