Resolution of Planar-Chiral Ferrocenylborane Lewis Acids: The Impact of Steric Effects on the Stereoselective Binding of Ephedrine Derivatives

2009 ◽  
Vol 28 (14) ◽  
pp. 4141-4149 ◽  
Author(s):  
Ramez Boshra ◽  
Krishnan Venkatasubbaiah ◽  
Ami Doshi ◽  
Frieder Jäkle
Keyword(s):  
Lewis Acids ◽  
Steric Effects ◽  
Ephedrine Derivatives ◽  
The Impact

scholarly journals Reactive modeling of the initial stages of alkoxysilane polycondensation: effects of precursor molecule structure and solution composition

Soft Matter ◽  
2015 ◽  
Vol 11 (34) ◽  
pp. 6780-6789 ◽  
Author(s):  
Joshua D. Deetz ◽  
Roland Faller
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Steric Effects ◽  
Solution Composition ◽  
Precursor Molecule ◽  
Molecule Structure ◽  
Reactive Molecular Dynamics ◽  
Water Composition ◽  
Dynamics Simulations ◽  
The Impact

Reactive molecular dynamics simulations are used to model polycondensation of alkoxysilanes in solution. Different precursor monomers are compared and steric effects on polycondensation kinetics are observed. The impact of the alcohol and water composition in solution are explored.

scholarly journals Impact of AlCl3 and FeCl2 Addition on Catalytic Behaviors of TiCl4/MgCl2/THF Catalysts for Ethylene Polymerization and Ethylene/1-Hexene Copolymerization

2018 ◽  
Vol 13 (3) ◽  
pp. 393
Author(s):  
Thanyathorn Niyomthai ◽  
Bunjerd Jongsomjit ◽  
Piyasan Praserthdam
Keyword(s):  
Catalytic Activity ◽  
Active Center ◽  
Chemical Reaction ◽  
Lewis Acids ◽  
Ethylene Polymerization ◽  
Active Sites ◽  
Reaction Engineering ◽  
Chemical Route ◽  
The Impact ◽  
Chemical Reaction Engineering

The present research focuses on elucidating of the impact of Lewis acids including AlCl3 and FeCl2 addition on catalytic behaviors during ethylene polymerization and ethylene/1-hexene copolymerization over the TiCl4/MgCl2/THF catalyst (Cat. A). In this study, the Cat. A with the absence and presence of Lewis acids was synthesized via the chemical route. Then, all catalyst samples were characterized and tested in the slurry polymerization. For ethylene polymerization, using the Cat. A with the presence of AlCl3 apparently gave the highest activity among other catalysts. In addition, the activity of catalysts tended to increase with the presence of the Lewis acids. This can be attributed to an enhancement of active center distribution by the addition of Lewis acids leading to larger amounts of the isolated Ti species. Moreover, with the presence of Lewis acids, the effect of hydrogen on the decreased activity was also less pronounced. Considering ethylene/1-hexene copolymerization, it revealed that the catalyst with the presence of mixed Lewis acids (AlCl3 + FeCl2) exhibited the highest activity. It is suggested that the presence of mixed Lewis acids possibly caused a change in acidity of active sites, which is suitable for copolymerization. However, activities of all catalysts in ethylene/1-hexene copolymerization were lower than those in ethylene polymerization. The effect of hydrogen on the decreased activity for both polymerization and copolymerization system was found to be similar with the presence of Lewis acids. Based on this study, it is quite promising to enhance the catalytic activity by addition of proper Lewis acids, especially when the pressure of hydrogen increases. The characteristics of polymers obtained upon the presence of Lewis acids will be discussed further in more detail.  Copyright © 2018 BCREC Group. All rights reservedReceived: 22nd January 2018; Revised: 18th March 2018; Accepted: 19th March 2018How to Cite: Niyomthai, T., Jongsomjit, B., Praserthdam, P. (2018). Impact of AlCl3 and FeCl2 Addition on Catalytic Behaviors of TiCl4/MgCl2/THF Catalysts for Ethylene Polymerization and Ethylene/1-Hexene Copolymerization. Bulletin of Chemical Reaction Engineering & Catalysis, 13 (3): 393-404 (doi:10.9767/bcrec.13.3.2116.393-404)Permalink/DOI: https://doi.org/10.9767/bcrec.13.3.2116.393-404

scholarly journals The impact of interplay between electronic and steric effects on the synthesis and the linear and non-linear optical properties of diketopyrrolopyrrole bearing benzofuran moieties

2017 ◽  
Vol 4 (5) ◽  
pp. 724-736 ◽  
Author(s):  
Anna Purc ◽  
Beata Koszarna ◽  
Irina Iachina ◽  
Daniel H. Friese ◽  
Mariusz Tasior ◽  
...  
Keyword(s):  
Optical Properties ◽  
Steric Effects ◽  
Non Linear ◽  
Linear Optical Properties ◽  
Linear Optical ◽  
The Impact ◽  
Electronic And Steric Effects

Benzofuran has been proven to be the versatile substituent for tuning the optics of diketopyrrolopyrroles.

Formation of Lunar Craters and Bright Rays as a Result of Meteorite Impacts

1962 ◽  
Vol 14 ◽  
pp. 415-418
Author(s):  
K. P. Stanyukovich ◽  
V. A. Bronshten
Keyword(s):  
Explosive Charge ◽  
The Moon ◽  
Meteorite Impacts ◽  
The Earth ◽  
Lunar Craters ◽  
The Impact

The phenomena accompanying the impact of large meteorites on the surface of the Moon or of the Earth can be examined on the basis of the theory of explosive phenomena if we assume that, instead of an exploding meteorite moving inside the rock, we have an explosive charge (equivalent in energy), situated at a certain distance under the surface.

The Geosciences Applied to Lunar Exploration

1962 ◽  
Vol 14 ◽  
pp. 169-257 ◽  
Author(s):  
J. Green
Keyword(s):  
Lunar Surface ◽  
Probable Mechanism ◽  
Point Of View ◽  
Lunar Exploration ◽  
Geological Model ◽  
Apply Geophysics ◽  
Surface Features ◽  
The Impact

The term geo-sciences has been used here to include the disciplines geology, geophysics and geochemistry. However, in order to apply geophysics and geochemistry effectively one must begin with a geological model. Therefore, the science of geology should be used as the basis for lunar exploration. From an astronomical point of view, a lunar terrain heavily impacted with meteors appears the more reasonable; although from a geological standpoint, volcanism seems the more probable mechanism. A surface liberally marked with volcanic features has been advocated by such geologists as Bülow, Dana, Suess, von Wolff, Shaler, Spurr, and Kuno. In this paper, both the impact and volcanic hypotheses are considered in the application of the geo-sciences to manned lunar exploration. However, more emphasis is placed on the volcanic, or more correctly the defluidization, hypothesis to account for lunar surface features.

Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics

1997 ◽  
Vol 161 ◽  
pp. 197-201 ◽  
Author(s):  
Duncan Steel
Keyword(s):  
Probability Distributions ◽  
Regions Of Interest ◽  
Significant Fraction ◽  
Organic Chemicals ◽  
Impact Speed ◽  
The Mean ◽  
The Impact

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.

Organic Syntheses During the Impact of a Comet with a Gaseous Planet

1997 ◽  
Vol 161 ◽  
pp. 189-195
Author(s):  
Cesare Guaita ◽  
Roberto Crippa ◽  
Federico Manzini
Keyword(s):  
Polymeric Material ◽  
Molecular Form ◽  
Parent Compound ◽  
Blue Filter ◽  
Organic Syntheses ◽  
The Impact

AbstractA large amount of CO has been detected above many SL9/Jupiter impacts. This gas was never detected before the collision. So, in our opinion, CO was released from a parent compound during the collision. We identify this compound as POM (polyoxymethylene), a formaldehyde (HCHO) polymer that, when suddenly heated, reformes monomeric HCHO. At temperatures higher than 1200°K HCHO cannot exist in molecular form and the most probable result of its decomposition is the formation of CO. At lower temperatures, HCHO can react with NH3 and/or HCN to form high UV-absorbing polymeric material. In our opinion, this kind of material has also to be taken in to account to explain the complex evolution of some SL9 impacts that we observed in CCD images taken with a blue filter.

Hydrogen Cyanide Polymers from the Impact of Comet P/Shoemaker-Levy 9 on Jupiter

1997 ◽  
Vol 161 ◽  
pp. 179-187
Author(s):  
Clifford N. Matthews ◽  
Rose A. Pesce-Rodriguez ◽  
Shirley A. Liebman
Keyword(s):  
Amino Acids ◽  
Solar System ◽  
Hydrogen Cyanide ◽  
Nitrogen Heterocycles ◽  
Laboratory Studies ◽  
Heterogeneous Solids ◽  
The Many ◽  
Comet Halley ◽  
The Impact ◽  
By Products

AbstractHydrogen cyanide polymers – heterogeneous solids ranging in color from yellow to orange to brown to black – may be among the organic macromolecules most readily formed within the Solar System. The non-volatile black crust of comet Halley, for example, as well as the extensive orangebrown streaks in the atmosphere of Jupiter, might consist largely of such polymers synthesized from HCN formed by photolysis of methane and ammonia, the color observed depending on the concentration of HCN involved. Laboratory studies of these ubiquitous compounds point to the presence of polyamidine structures synthesized directly from hydrogen cyanide. These would be converted by water to polypeptides which can be further hydrolyzed to α-amino acids. Black polymers and multimers with conjugated ladder structures derived from HCN could also be formed and might well be the source of the many nitrogen heterocycles, adenine included, observed after pyrolysis. The dark brown color arising from the impacts of comet P/Shoemaker-Levy 9 on Jupiter might therefore be mainly caused by the presence of HCN polymers, whether originally present, deposited by the impactor or synthesized directly from HCN. Spectroscopic detection of these predicted macromolecules and their hydrolytic and pyrolytic by-products would strengthen significantly the hypothesis that cyanide polymerization is a preferred pathway for prebiotic and extraterrestrial chemistry.

Unusual Microstructure in Shock-Compacted Graphite

1970 ◽  
Vol 28 ◽  
pp. 474-475
Author(s):  
Lucien F. Trueb
Keyword(s):  
Mechanical Characteristic ◽  
Compression Wave ◽  
Gray Zone ◽  
Flyer Plate ◽  
Compacted Graphite ◽  
The Impact

Crushed and statically compressed Madagascar graphite that was explosively shocked at 425 kb by means of a planar flyer-plate is characterized by a black zone extending for 2 to 3 nun below the impact plane of the driver. Beyond this point, the material assumes the normal gray color of graphite. The thickness of the black zone is identical with the distance taken by the relaxation wave to overtake the compression wave.The main mechanical characteristic of the black material is its great hardness; steel scalpels and razor blades are readily blunted during attempts to cut it. An average microhardness value of 95-3 DPHN was obtained with a 10 kg load. This figure is a minimum because the indentations were usually cracked; 14.8 DPHN was measured in the gray zone.

Drug Induced Changes in Cell Organelles

1968 ◽  
Vol 26 ◽  
pp. 110-111
Author(s):  
Sarah A. Luse
Keyword(s):  
Clinical Medicine ◽  
Cell Organelles ◽  
Riboflavin Deficiency ◽  
Drug Induced ◽  
New Era ◽  
Health And Disease ◽  
In The Beginning ◽  
Cellular Pathology ◽  
Induced Changes ◽  
The Impact

In the mid-nineteenth century Virchow revolutionized pathology by introduction of the concept of “cellular pathology”. Today, a century later, this term has increasing significance in health and disease. We now are in the beginning of a new era in pathology, one which might well be termed “organelle pathology” or “subcellular pathology”. The impact of lysosomal diseases on clinical medicine exemplifies this role of pathology of organelles in elucidation of disease today.Another aspect of cell organelles of prime importance is their pathologic alteration by drugs, toxins, hormones and malnutrition. The sensitivity of cell organelles to minute alterations in their environment offers an accurate evaluation of the site of action of drugs in the study of both function and toxicity. Examples of mitochondrial lesions include the effect of DDD on the adrenal cortex, riboflavin deficiency on liver cells, elevated blood ammonia on the neuron and some 8-aminoquinolines on myocardium.

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