Stereochemical investigation of the initiation step in MgCl2-supported Ziegler-Natta catalysts: the Lewis base activation effect

1990 ◽  
Vol 23 (2) ◽  
pp. 383-386 ◽  
Author(s):  
Maria Carmela Sacchi ◽  
Chengji Shan ◽  
Paolo Locatelli ◽  
Incoronata Tritto
Keyword(s):  
Lewis Base ◽  
Activation Effect ◽  
Initiation Step ◽  
Ziegler Natta Catalysts

Activation effect of alkoxysilanes as external donors in magnesium chloride-supported Ziegler-Natta catalysts

1992 ◽  
Vol 25 (22) ◽  
pp. 5914-5918 ◽  
Author(s):  
Maria Carmela Sacchi ◽  
Fabrizio Forlini ◽  
Incoronata Tritto ◽  
Raniero Mendichi ◽  
Giulio Zannoni ◽  
...  
Keyword(s):  
Magnesium Chloride ◽  
Activation Effect ◽  
Ziegler Natta Catalysts

Mechanistic aspects in propene polymerization using mgcl2-supported ziegler-natta catalysts: behaviour of silane as an external lewis base

1989 ◽  
Vol 56 (1-3) ◽  
pp. 156-169 ◽  
Author(s):  
Roger Spitz ◽  
Charles Bobichon ◽  
Marie-France Llauro-Darricades ◽  
Alain Guyot ◽  
Laurent Duranel
Keyword(s):  
Lewis Base ◽  
Propene Polymerization ◽  
Ziegler Natta Catalysts

High time resolution enzyme cytochemistry of rod outer segment

1990 ◽  
Vol 48 (3) ◽  
pp. 878-879
Author(s):  
Takuma Saito ◽  
Toshihiro Takizawa
Keyword(s):  
Enzyme Activities ◽  
Outer Segment ◽  
Rapid Change ◽  
High Time Resolution ◽  
Visual Cell ◽  
Enzyme Cytochemistry ◽  
Activation Effect ◽  
Rod Outer Segment ◽  
Enzymatic Cascades ◽  
Rapid Drop

Cells and tissues live on a number of dynamic metabolic pathways, which are made up of sequential enzymatic cascades.Recent biochemical and physiological studies of vision research showed the importance of cGMP metabolism in the rod outer segment of visual cell, indicat ing that the photon activated rhodopsin exerts activation effect on the GTP binding protein, transducin, and this act ivated transducin further activates phosphodiesterase (PDEase) to result in a rapid drop in cGMP concentration in the cytoplasm of rod outer segment. This rapid drop of cGMP concentration exerts to close the ion channel on the plasma membrane and to stop of inward current brings hyperpolarization and evokes an action potential.These sequential change of enzyme activities, known as cGMP cascade, proceeds quite rapidly within msec order. Such a rapid change of enzyme activities, such as PDEase in rod outer segment, was not a matter of conventional histochemical invest igations.

Can the Lewis basicity of an isolated solvent molecule be used for characterizing solvent effects?

2020 ◽  
Vol 16 ◽  
Author(s):  
Jean-François Gal ◽  
Pierre-Charles Maria
Keyword(s):  
Solvent Effects ◽  
Molecular Level ◽  
Solvent Molecule ◽  
Lewis Base ◽  
Bulk Liquid ◽  
Donor Number ◽  
Special Focus ◽  
Solution Processes ◽  
Inert Solvent

Background: The ubiquitous Lewis acid/base interactions are important in solution processes. Analytical chemistry may benefit of a better understanding of the role of Lewis basicity, at the molecular level or acting through a bulk solvent effect. Objective: To clearly delineate (i) the basicity at a molecular level, hereafter referred as solute basicity, and (ii) the solvent basicity, which is a bulk-liquid property. Method: The literature that relates Lewis basicity scales and solvent effects is analyzed. A special focus is placed on two extensive scales, the Donor Number, DN, and the BF3 affinity scale, BF3A, which were obtained by calorimetric measurement on molecules as solutes diluted in a quasi-inert solvent, and therefore define a molecular Lewis basicity. We discuss the validity of these solute scales when regarded as solvent scales, in particular when the basicity of strongly associated liquids is discussed. Results: We demonstrate the drawbacks of confusing the Lewis basicity of a solvent molecule, isolated as solute, and that of the bulk liquid solvent itself. Conclusion: Consequently, we recommend a reasoned use of the concept of Lewis basicity taking clearly into account the specificity of the process for which a Lewis basicity effect may be invoked. In particular, the action of the Lewis base, either as an isolated entity, or as a bulk liquid, must be distinguished.

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