scholarly journals Oxygen Adsorption and Activation on Cobalt Center in Modified Keggin Anion-DFT Calculations

Catalysts ◽  
2020 ◽  
Vol 10 (2) ◽  
pp. 144
Author(s):  
Renata Tokarz-Sobieraj ◽  
Piotr Niemiec
Keyword(s):  
Negative Charge ◽  
Calculated Data ◽  
Oxygen Adsorption ◽  
Keggin Anion ◽  
Cobalt Cation ◽  
Keggin Anions ◽  
Active Channels ◽  
Solvent Molecules ◽  
Cation Complexes ◽  
Cobalt Center

The influence of the cobalt cation geometric environment on catalytic activity, namely, oxygen adsorption and its activation, was investigated by exploring two groups of systems. The first group was formed by cobalt cation complexes, in which the Co2+ was surrounded by water-H2O or acetonitrile-CH3CN solvent molecules. This represents heteropolyacids salts (ConH3-nPW(Mo)12O40), where the Co2+ acts as a cation that compensates for the negative charge of the Keggin anion and is typically surrounded by solvent molecules in that system. The second group consisted of tungsten or molybdenum Keggin anions (H5PW11CoO39 and H5PMo11CoO39), having the Co2+ cation incorporated into the anion framework, in the position of one addenda atom. Detailed NOCV (Natural Orbitals for Chemical Valence) analysis showed that, for all studied systems, the σ-donation and σ-backdonation active channels of the electron transfer were responsible for the creation of a single Co-OO bond. Depending on the chemical/geometrical environment of the Co2+ cation, the different quantities of electrons were flown from the Co2+ 3d orbital to the π* antibonding molecular orbitals of the oxygen ligand, as well as in the opposite direction. In molybdenum and tungsten heteropolyacids, modified by Co2+ in the position of the addenda atom, activation of O2 was supported by a π-polarization process. Calculated data show that the oxygen molecule activation changed in the following order: H5PMo11CoO39 = H5PW11CoO39 > Co(CH3CN)52+ > Co(H2O)52+.

Missile Deployment: Nucleophilic Substitution

Reactions ◽  
2011 ◽  
Author(s):  
Peter Atkins
Keyword(s):  
Nucleophilic Substitution ◽  
Electric Charge ◽  
Negative Charge ◽  
Positive Charge ◽  
Target Atom ◽  
Electron Cloud ◽  
Target Molecule ◽  
New Construction ◽  
Solvent Molecules ◽  
Electron Clouds

The equivalent of a heat-seeking missile in chemistry is a ‘nucleophile’, a lover of nuclei. The ‘missile’ in this case is a special sort of molecule which sniffs out not heat but positive electric charge, the charge of a nucleus glinting through depleted regions of electron cloud in a target molecule. A candidate for such a missile is a negatively charged ion, which can be attracted to the partially exposed positive charge of a nucleus in the target. With nucleus-sniffing in mind, you can perhaps appreciate that if it is possible to blow away some of the electron cloud from the region of a particular C atom in the target molecule, then the nucleophile will home in on that atom and perhaps attach to it. By management of the electron clouds and adroit choice of the incoming missile, therefore, it is possible to build where and what we want. You shouldn’t lose sight of the fact that the ‘missile’ doesn’t just fly through the air and smash into a molecule: it jostles past the solvent molecules, which move aside or sometimes block it and turn it back. When thinking about the reactions in this section, think of the target atom in a molecule as glowing with positive charge and the incoming missile, the reagent, as having an abundance of negative charge spread over at least one of its atoms. The target and missile are drawn together through the solvent, and might snap together, in a manner I shall describe, once they are close to one another. A missile’s successful hunt for a target might then result in reaction and the formation of a new compound. How are the target prepared and the missile launched? One procedure is to go the whole electrical hog and prepare a molecule with a full positive charge on the C atom that has been chosen to be the foundation of the new construction, the proposed site of reaction. The whole hog can be achieved by snipping out an atom that initially is attached to the C atom.

scholarly journals Crystal structure of bromidopentakis(tetrahydrofuran-κO)magnesium bis[1,2-bis(diphenylphosphanyl)benzene-κ2 P,P′]cobaltate(−1) tetrahydrofuran disolvate

2019 ◽  
Vol 75 (2) ◽  
pp. 304-307
Author(s):  
Patience B. Girigiri ◽  
Stephanie H. Carpenter ◽  
William W. Brennessel ◽  
Michael L. Neidig
Keyword(s):  
Crystal Structure ◽  
Structural Characterization ◽  
Solvent Molecule ◽  
Title Complex ◽  
Tetrahedral Geometry ◽  
Π Interactions ◽  
Packing Arrangement ◽  
Solvent Molecules ◽  
Cobalt Center

Structural characterization of the ionic title complex, [MgBr(THF)5][Co(dpbz)2]·2THF [THF is tetrahydrofuran, C4H8O; dpbz is 1,2-bis(diphenylphosphanyl)benzene, C30H24P2], revealed a well-separated cation and anion co-crystallized with two THF solvent molecules that interact with the cation via weak C—H...O contacts. The geometry about the cobalt center is pseudotetrahedral, as is expected for a d 10 metal center, only deviating from an ideal tetrahedral geometry because of the restrictive bite angles of the bidentate phosphane ligands. Three THF ligands of the cation and one co-crystallized THF solvent molecule are each disordered over two orientations. In the extended structure, the cations and THF solvent molecules are arranged in (100) sheets that alternate with layers of anions, the latter of which show various π-interactions, which may explain the particular packing arrangement.

scholarly journals Composition and Nano-Periodic Structure of Compounds Formed by the Reaction of Molybdenum and Tungsten Heteropolyanions with Cationic Surfactants1

1998 ◽  
Vol 16 (9) ◽  
pp. 685-695
Author(s):  
A.P. Filippov ◽  
A.S. Kovalenko ◽  
V.G. Il'in
Keyword(s):  
Room Temperature ◽  
Ph Value ◽  
Periodic Structures ◽  
Reaction Medium ◽  
Surfactant Molecule ◽  
Keggin Anion ◽  
Acidic Media ◽  
Synthesis Conditions ◽  
Keggin Anions ◽  
Hydrophobic Tail

Keggin heteropolyanions (HPAns) of structure [PMo12O40]3– and [PW12O40]3– have been allowed to react in acidic media at room temperature with some cationic surfactants of the quaternary ammonium or primary amine type to yield meso-structured insoluble salts with the general formulae Am3[PM12O40], Etn3[PM12O40]2, Etn3[PM12O40]2•nEtnCl2 or AmnH7-n[PM11O39]•xH2O, where Am and Etn are, respectively, mono- and di-cationic surfactant species, M is Mo or W and n can vary in the range 0 to ∼3. All of the materials obtained possessed nano-periodic structures whose maximum d100 parameters ranged from 26 Å to 36 Å, exhibiting lamellar, tetragonal, hexagonal or cubic meso structures depending on the synthesis conditions employed and the nature of the surfactant and HPAns used. The values of the highest d100 parameter obtained for the substances prepared were generally in line with the length of the hydrophobic tail in the surfactant molecule but less dependent on the nature of the metal (Mo or W) when the latter was incorporated in a Keggin anion. However, the structure of the materials was considerably influenced by the pH value of the reaction medium and the P/M ratio when transformation of the Keggin anions into lacunary or other anions was possible.

Towards a computational treatment of polyoxometalates in solution using QM methods and explicit solvent molecules

2009 ◽  
Vol 87 (10) ◽  
pp. 1296-1301 ◽  
Author(s):  
Pere Miró ◽  
Josep M. Poblet ◽  
Josep Bonet Ávalos ◽  
Carles Bo
Keyword(s):  
Single Point ◽  
Solvation Energy ◽  
Solvation Shell ◽  
Keggin Anion ◽  
Charged Species ◽  
Counter Ions ◽  
Explicit Solvent ◽  
Solvent Model ◽  
Explicit Solvent Model ◽  
Solvent Molecules

This study is aimed at developing an explicit solvent model for highly charged species such as polyoxometalates. The model includes solvent molecules in the first solvation shell explicitly, and long-range bulk effects and counter-ions as a set of single point charges. The model strongly stabilizes the electronic structure of the Keggin anion. The energies of the Kohn–Sham orbitals obtained using our model lie very close to those computed using the COSMO continuum solvent model; moreover, the total solvation energy evaluated with our model compares well to the value calculated by COSMO.

The Fine Structure of Glycocalyx in Human Spermatozoa. A High Resolution Cytochemical Study

1973 ◽  
Vol 31 ◽  
pp. 640-641
Author(s):  
P. Hernández-Jáuregui ◽  
A. Sosa ◽  
A. González Angulo
Keyword(s):  
Negative Charge ◽  
Iron Hydroxide ◽  
Human Spermatozoa ◽  
Surface Coat ◽  
Cell Surfaces ◽  
Colloidal Iron ◽  
Cytochemical Study ◽  
Specific Permeability ◽  
Extracellular Glycoprotein ◽  
Mammalian Spermatozoa

Glycocalyx is the name given by Bennett to the extracellular glycoprotein coat present in some cell surfaces. It appears to play an important role in cell properties such as antigenicity, cell adhesivity, specific permeability, and ATP ase activity. In the sperm this coat can be directly related to such important phenomena as capacitation and fertilization. The presence of glycocalyx in invertebrate spermatozoa has already been demonstrated. Recently Yanagimachi et al. has determined the negative charges on sperm surfaces of mammalian spermatozoa including man, using colloidal iron hydroxide. No mention was made however of the outer surface coat as composed of substances other than those confering a negative charge. The purpose of this work was therefore to determine the presence of a glycocalyx in human spermatozoa using alcian blue and lanthanum staining.

The Action of Thrombin on Modified Fibrinogen

1983 ◽  
Vol 49 (03) ◽  
pp. 208-213
Author(s):  
A J Osbahr
Keyword(s):  
Physical Properties ◽  
Negative Charge ◽  
Lysine Residue ◽  
Fibrinopeptide A ◽  
Amino Groups ◽  
Lysine Residues ◽  
Citraconic Anhydride

SummaryThe modification of canine fibrinogen with citraconic anhydride modified the ε-amino groups of the fibrinogen and at the same time generated additional negative charges into the protein. The addition of thrombin to the modified fibrinogen did not induce polymerization; however, the fibrinopeptide was released at a faster rate than from the unmodified fibrinogen. The physical properties of the citraconylated fibrinogen were markedly altered by the modification of 50-60 lysine residues in one hour. A modified fibrinopeptide-A was released by thrombin from the modified fibrinogen and was electrophoretically more anionic than the unmodified fibrinopeptide-A. Edman analysis confirmed the modification of the lysine residue present in the peptide. The rate of removal of citraconylated fibrinopeptide-A from modified fibrinogen by thrombin was 30 to 40 percent greater than the cleavage of unmodified fibrinopeptide-A from unmodified fibrinogen. However, the modification of 60 or more lysine residues in the fibrinogen produced a decrease in the rate of cleavage of citraconylated fibrinopeptide-A. The results suggest that additional negative charge in the vicinity of the attachment of fibrinopeptide-A to canine fibrinogen aids in the removal of the peptide by thrombin.

Prediction of root damaging during mechanical shaking of fruit trees

2014 ◽  
Vol 10 (1) ◽  
pp. 1-15
Author(s):  
Z. Láng
Keyword(s):  
Field Experiments ◽  
Calculated Data ◽  
Fruit Trees ◽  
List Type ◽  
Structure Model ◽  
Root Damage ◽  
Set Up ◽  
Simple Tree ◽  
The Given ◽  
Cherry Trees

The possible effect of shaker harvest on root damage of 10-year-old cherry trees was studied on a simple tree structure model. The model was composed of elastic trunk and rigid main roots, the ends of which were connected to the surrounding soil via springs and dumping elements. Equations were set up to be able to calculate the relation between shaking height on the trunk and strain in the roots. To get the data for root break and their elongation at different shaking heights on the trunk, laboratory and field experiments were carried out on cherry trees and on their roots. Having evaluated the measured and calculated data it could be concluded that root damage is to be expected even at 3.6% strain and the risk of it increases with increased trunk amplitudes, i.e.with the decrease of shaking heightat smaller stem diameters (i.e. in younger plantation), andif the unbalanced mass of the shaker machine is too large for the given tree size.

Thermoelectric Properties of PbSr(Se,Te)-Based Low Dimensional Structures

2000 ◽  
Vol 626 ◽  
Author(s):  
Harald Beyer ◽  
Joachim Nurnus ◽  
Harald Böttner ◽  
Armin Lambrecht ◽  
Lothar Schmitt ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermoelectric Properties ◽  
Power Factor ◽  
Evaluation Method ◽  
Interband Transition ◽  
Multiple Quantum Well ◽  
Calculated Data ◽  
Multiple Quantum ◽  
Ir Transmission ◽  
Low Dimensional

ABSTRACTThermoelectric properties of low dimensional structures based on PbTe/PbSrTe-multiple quantum-well (MQW)-structures with regard to the structural dimensions, doping profiles and levels are presented. Interband transition energies and barrier band-gap are determined from IR-transmission spectra and compared with Kronig-Penney calculations. The influence of the data evaluation method to obtain the 2D power factor will be discussed. The thermoelectrical data of our layers show a more modest enhancement in the power factor σS2 compared with former publications and are in good agreement with calculated data from Broido et al. [5]. The maximum allowed doping level for modulation doped MQW structures is determined. Thermal conductivity measurements show that a ZT enhancement can be achieved by reducing the thermal conductivity due to interface scattering. Additionally promising lead chalcogenide based superlattices for an increased 3D figure of merit are presented.

Electron beam induced effects in Cu/GeSe2amorphous films

2003 ◽  
Vol 777 ◽  
Author(s):  
J.S. Romero ◽  
A.G. Fitzgerald
Keyword(s):  
Thin Films ◽  
Electron Beam ◽  
Simple Model ◽  
Copper Concentration ◽  
Negative Charge ◽  
Electron Bombardment ◽  
Continuous Operation ◽  
Electron Radiation ◽  
Crystalline Product ◽  
Intense Electron

AbstractCopper migration is observed in the SEM in amorphous GeSe2/Cu thin films when an electron beam is focused in pulsed or continuous operation on the surface of these thin films. The phenomenon can be explained using a simple model in which the population of D- centers is considered to increase upon electron irradiation. The increase in the D- center population is envisaged as due to the breaking of bonds by the electron radiation and by the constant presence of negative charge in irradiated regions. Changes in copper concentration of 20%-30% have been obtained. Additionally we have observed the local crystallization of amorphous GeSe2/Cu thin films in the TEM when the samples were subjected to intense electron bombardment. The crystalline product has been identified as Berzelianite (Cu2Se).

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