Renaissance of Homogeneous Cerium Catalysts with Unique     Ce(IV/III) Couple: Redox-Mediated Organic Transformations Involving Homolysis of Ce(IV)–Ligand Covalent Bonds

2021 ◽  
Author(s):  
Hayato Tsurugi ◽  
Kazushi Mashima
Keyword(s):  
Organic Transformations ◽  
Covalent Bonds ◽  
Cerium Catalysts

Introduction of a new ionic liquid solid acid based on clay as an efficient, recyclable and thermally stable catalyst for organic transformations

RSC Advances ◽  
2016 ◽  
Vol 6 (24) ◽  
pp. 20306-20316 ◽  
Author(s):  
Somayyeh Sarvi Beigbaghlou ◽  
Katayoun Marjani ◽  
Azizollah Habibi ◽  
Seyyed Vahid Atghia
Keyword(s):  
Ionic Liquid ◽  
Solid Acid ◽  
Thermally Stable ◽  
Hydrogen Sulfate ◽  
Organic Transformations ◽  
Sodium Montmorillonite ◽  
Covalent Bonds ◽  
Stable Catalyst ◽  
Ammonium Hydrogen ◽  
Ammonium Hydrogen Sulfate

Ammonium hydrogen sulfate based ionic liquid immobilized on Na+–montmorillonite (AHS@MMT) was prepared via anchoring ammonium hydrogen sulfate propyltriethoxysilane onto sodium montmorillonite by covalent bonds.

Baker’s Yeast-Based Organocatalysis: Applications in Organic Synthesis

2019 ◽  
Vol 6 (2) ◽  
pp. 158-164
Author(s):  
Biswa Mohan Sahoo ◽  
Bimal Krishna Banik
Keyword(s):  
Organic Synthesis ◽  
Baker’S Yeast ◽  
Organic Reactions ◽  
Hydroxyl Group ◽  
High Yield ◽  
Baker's Yeast ◽  
Organic Transformations ◽  
Covalent Bonds ◽  
Chemical Catalysis ◽  
Oxidation Reduction

Background: Catalyst speeds up any chemical reaction without changing the point of the equilibrium. Catalysis process plays a key role in organic synthesis to produce new organic compounds. Similarly, organocatalysis is a type of chemical catalysis in which the rate of a reaction is accelerated by organic catalysts. Methods: Organocatalysts have gained significant utility in organic reactions due to their less of sensitivity towards moisture, readily available, economic, large chiral pool and low toxicity as compared to metal catalysts. Organocatalysts work via both formations of covalent bonds such as enamine and iminium catalysis as well as through non-covalent interactions such as in hydrogen bonding. For example, Bakers’ yeast based organocatalysis is widely used in various organic transformations. Results: Baker’s yeast is a fermentation product and used mainly in the preparation of bread dough. It is produced by aerobic fermentation of yeast strain Saccharomyces cerevisiae. Baker's yeast consists of enzymes which can reduce a carbonyl group into a hydroxyl group with high yield and thereby making it suitable for biotransformations in organic synthesis. Conclusion: Baker's yeast is widely used as a biocatalyst in various organic reactions such as oxidation, reduction, condensation, hydrolysis, cyclization, etc. because it is readily available, inexpensive and easy to handle.

Temperature Dependence of the Critical Electron Dose for Fatty Acid Monolayers

1982 ◽  
Vol 40 ◽  
pp. 78-79
Author(s):  
Kenneth H. Downing ◽  
Robert M. Glaeser
Keyword(s):  
Electron Beam ◽  
Fatty Acid ◽  
Inelastic Scattering ◽  
Temperature Dependence ◽  
Structural Damage ◽  
Direct Result ◽  
Second Step ◽  
Strong Temperature Dependence ◽  
Electron Dose ◽  
Covalent Bonds

The structural damage of molecules irradiated by electrons is generally considered to occur in two steps. The direct result of inelastic scattering events is the disruption of covalent bonds. Following changes in bond structure, movement of the constituent atoms produces permanent distortions of the molecules. Since at least the second step should show a strong temperature dependence, it was to be expected that cooling a specimen should extend its lifetime in the electron beam. This result has been found in a large number of experiments, but the degree to which cooling the specimen enhances its resistance to radiation damage has been found to vary widely with specimen types.

Structural Transformation of a Germanium Σ=13 (510) [001] Tilt Grain Boundary under the Electron Beam

1990 ◽  
Vol 48 (1) ◽  
pp. 52-53 ◽  
Author(s):  
Jean-Luc Rouvière ◽  
Alain Bourret
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Grain Boundary ◽  
Structural Transformation ◽  
Mirror Symmetry ◽  
High Resolution Electron Microscopy ◽  
Structural Transformations ◽  
Covalent Bonds ◽  
Resolution Electron ◽  
Tilt Grain Boundary

The possible structural transformations during the sample preparations and the sample observations are important issues in electron microscopy. Several publications of High Resolution Electron Microscopy (HREM) have reported that structural transformations and evaporation of the thin parts of a specimen could happen in the microscope. Diffusion and preferential etchings could also occur during the sample preparation.Here we report a structural transformation of a germanium Σ=13 (510) [001] tilt grain boundary that occurred in a medium-voltage electron microscopy (JEOL 400KV).Among the different (001) tilt grain boundaries whose atomic structures were entirely determined by High Resolution Electron Microscopy (Σ = 5(310), Σ = 13 (320), Σ = 13 (510), Σ = 65 (1130), Σ = 25 (710) and Σ = 41 (910), the Σ = 13 (510) interface is the most interesting. It exhibits two kinds of structures. One of them, the M-structure, has tetracoordinated covalent bonds and is periodic (fig. 1). The other, the U-structure, is also tetracoordinated but is not strictly periodic (fig. 2). It is composed of a periodically repeated constant part that separates variable cores where some atoms can have several stable positions. The M-structure has a mirror glide symmetry. At Scherzer defocus, its HREM images have characteristic groups of three big white dots that are distributed on alternatively facing right and left arcs (fig. 1). The (001) projection of the U-structure has an apparent mirror symmetry, the portions of good coincidence zones (“perfect crystal structure”) regularly separate the variable cores regions (fig. 2).

Imine Based Self-Healing Hydrogel Triggered by Periodate

2020 ◽  
Author(s):  
Alexis Wolfel ◽  
Cecilia Inés Alvarez Igarzabal ◽  
Marcelo Ricardo Romero
Keyword(s):  
Functional Groups ◽  
Time Window ◽  
Crosslinking Reaction ◽  
Self Healing ◽  
Swelling Properties ◽  
Covalent Bonds ◽  
Smart Systems ◽  
Primary Amino ◽  
Vicinal Diols ◽  
Aldehyde Groups

<p>Design of materials with novel sensitivities and smart behaviour is important for the development of smart systems with automated responsiveness. We have recently reported the synthesis of hydrogels, cross-linked by <i>N,N'</i>-diallyltartardiamide (DAT). The covalent DAT-crosslinking points have vicinal diols which can be easily cleaved with periodate, generating valuable a-oxo-aldehyde functional groups, useful for further chemical modification. Based on those findings, we envisioned that a self-healable hydrogel could be obtained by incorporation of primary amino functional groups, from <a>2-aminoethyl methacrylate </a>hydrochloride (AEMA), coexisting with DAT into the same network. The a-oxo-aldehyde groups generated after the reaction with periodate would arise in the immediate environment of amine groups to form imine cross-links. For this purpose, DAT-crosslinked hydrogels were synthesized and carefully characterized. The cleavage of DAT-crosslinks with periodate promoted changes in the mechanical and swelling properties of the materials. As expected, a self-healing behavior was observed, based on the spontaneous formation of imine covalent bonds. In addition, we surprisingly found a combination of fast vicinal diols cleavage and a low speed self-crosslinking reaction by imine formation. Consequently, it was found a time-window in which a periodate-treated polymer was obtained in a transient liquid state, which can be exploited to choose the final shape of the material, before automated gelling. The singular properties attained on these hydrogels could be useful for developing sensors, actuators, among other smart systems.</p>

Seeded Growth of Single-Crystal Two-Dimensional Covalent Organic Frameworks

2017 ◽  
Author(s):  
Austin M. Evans ◽  
Lucas R. Parent ◽  
Nathan C. Flanders ◽  
Ryan P. Bisbey ◽  
Edon Vitaku ◽  
...  
Keyword(s):  
Molecular Transport ◽  
Controlled Synthesis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Seeded Growth ◽  
Covalent Bonds ◽  
Crystalline Materials ◽  
Step Procedure ◽  
Structures And Properties ◽  
2D Polymer

<div> <div> <div> <p>Polymerizing monomers into periodic two-dimensional (2D) networks provides structurally precise, atomically thin macromolecular sheets linked by robust, covalent bonds. These materials exhibit desirable mechanical, optoelectrotronic, and molecular transport properties derived from their designed structure and permanent porosity. 2D covalent organic frameworks (COFs) offer broad monomer scope, but are generally isolated as polycrystalline, insoluble powders with limited processability. Here we overcome this limitation by controlling 2D COF formation using a two- step procedure. In the first step, 2D COF nanoparticle seeds are prepared with approximate diameters of 30 nm. Next, monomers are slowly added to suppress new nucleation while promoting epitaxial growth on the existing seeds to sizes of several microns. The resulting COF nanoparticles are of exceptional and unprecedented quality, isolated as single crystalline materials with micron-scale domain sizes. These findings advance the controlled synthesis of 2D layered COFs and will enable a broad exploration of synthetic 2D polymer structures and properties. </p> </div> </div> </div>

Seeded Growth of Single-Crystal Two-Dimensional Covalent Organic Frameworks

2017 ◽  
Author(s):  
Austin M. Evans ◽  
Lucas R. Parent ◽  
Nathan C. Flanders ◽  
Ryan P. Bisbey ◽  
Edon Vitaku ◽  
...  
Keyword(s):  
Molecular Transport ◽  
Controlled Synthesis ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Seeded Growth ◽  
Covalent Bonds ◽  
Crystalline Materials ◽  
Step Procedure ◽  
Structures And Properties ◽  
2D Polymer

<div> <div> <div> <p>Polymerizing monomers into periodic two-dimensional (2D) networks provides structurally precise, atomically thin macromolecular sheets linked by robust, covalent bonds. These materials exhibit desirable mechanical, optoelectrotronic, and molecular transport properties derived from their designed structure and permanent porosity. 2D covalent organic frameworks (COFs) offer broad monomer scope, but are generally isolated as polycrystalline, insoluble powders with limited processability. Here we overcome this limitation by controlling 2D COF formation using a two- step procedure. In the first step, 2D COF nanoparticle seeds are prepared with approximate diameters of 30 nm. Next, monomers are slowly added to suppress new nucleation while promoting epitaxial growth on the existing seeds to sizes of several microns. The resulting COF nanoparticles are of exceptional and unprecedented quality, isolated as single crystalline materials with micron-scale domain sizes. These findings advance the controlled synthesis of 2D layered COFs and will enable a broad exploration of synthetic 2D polymer structures and properties. </p> </div> </div> </div>

Arylboronic Acids in Self-condensation of Glucosamines Forming Deoxyfructosazine, Catalysts or Reagents?

2019 ◽  
Author(s):  
Meifeng Wang ◽  
Gan Zhu ◽  
Yiqun Li ◽  
Liuqun Gu
Keyword(s):  
Molecular Recognition ◽  
Boric Acid ◽  
Boronic Acid ◽  
Catalytic Mechanism ◽  
Organic Transformations ◽  
Food Industries ◽  
Arylboronic Acids ◽  
Excess Amount ◽  
Phenyl Boronic Acid ◽  
Boron Acid

Arylboronic acids were widely used as efficient catalysts in direct amide formation and other organic transformations. Surprisingly, reports on their use as catalysts in carbohydrates synthesis are very rare even though boron acid-diol complexation was extensively investigated in molecular recognition for saccharides and so on. Here we developed an efficient arylboronic acids catalyzed dimerization of glucosamines forming deoxyfructosazine which is important compound in pharmaceutical and food industries, against a commonly held belief that excess amount of phenyl boronic acid (or boric acid) is a must. A catalytic mechanism was also proposed and arylboronic acids instead of their boronates was identified as catalysts.

QM/MM Simulations of Organic Phosphorus Adsorption at the Diaspore-Water Interface

2019 ◽  
Author(s):  
Prasanth Babu Ganta ◽  
Oliver Kühn ◽  
Ashour Ahmed
Keyword(s):  
Interaction Energy ◽  
Dynamics Simulation ◽  
Water Molecules ◽  
Hydroxyl Groups ◽  
Water Interface ◽  
Mineral Surfaces ◽  
Soil Mineral ◽  
Phosphorus Adsorption ◽  
Covalent Bonds ◽  
Binding Mechanisms

The phosphorus (P) immobilization and thus its availability for plants are mainly affected by the strong interaction of phosphates with soil components especially soil mineral surfaces. Related reactions have been studied extensively via sorption experiments especially by carrying out adsorption of ortho-phosphate onto Fe-oxide surfaces. But a molecular-level understanding for the P-binding mechanisms at the mineral-water interface is still lacking, especially for forest eco-systems. Therefore, the current contribution provides an investigation of the molecular binding mechanisms for two abundant phosphates in forest soils, inositol hexaphosphate (IHP) and glycerolphosphate (GP), at the diaspore mineral surface. Here a hybrid electrostatic embedding quantum mechanics/molecular mechanics (QM/MM) based molecular dynamics simulation has been applied to explore the diaspore-IHP/GP-water interactions. The results provide evidence for the formation of different P-diaspore binding motifs involving monodentate (M) and bidentate (B) for GP and two (2M) as well as three (3M) monodentate for IHP. The interaction energy results indicated the abundance of the GP B motif compared to the M one. The IHP 3M motif has a higher total interaction energy compared to its 2M motif, but exhibits a lower interaction energy per bond. Compared to GP, IHP exhibited stronger interaction with the surface as well as with water. Water was found to play an important role in controlling these diaspore-IHP/GP-water interactions. The interfacial water molecules form moderately strong H-bonds (HBs) with GP and IHP as well as with the diaspore surface. For all the diaspore-IHP/GP-water complexes, the interaction of water with diaspore exceeds that with the studied phosphates. Furthermore, some water molecules form covalent bonds with diaspore Al atoms while others dissociate at the surface to protons and hydroxyl groups leading to proton transfer processes. Finally, the current results confirm previous experimental conclusions indicating the importance of the number of phosphate groups, HBs, and proton transfers in controlling the P-binding at soil mineral surfaces.

EFEKTIVITAS MODEL PEMBELAJARAN KOOPERATIF TIPE TEAMS GAMES TOURNAMENT (TGT) BERBANTUAN MEDIA KARTU SOAL PADA SUB MATERI IKATAN KOVALEN KELAS X MIA DI SMA ISLAM HARUNIYAH PONTIANAK

2018 ◽  
Vol 6 (2) ◽  
Author(s):  
Zulfadhli Abdillah
Keyword(s):  
Student Learning ◽  
Learning Outcomes ◽  
Covalent Bond ◽  
Student Learning Outcomes ◽  
Learning Model ◽  
Covalent Bonds ◽  
Team Games ◽  
Bonding Material ◽  
Before And After ◽  
Tenth Grade

 This  study  is  motivated  by  the  low  learning  outcomes  in  the  Sub-covalent  Bond class of tenth-grade students, SMA Islam Haruniyah Pontianak. This problem is due to the  lack  of  students'  understanding  of  the  concept  of  Covalent  Bonds.  Therefore,  a proper learning model is required to improve students’ understanding of Covalent Bond concepts  based  on  the  characteristics  of  both  learning  materials    and  students.  This study  aimed  to  investigate  the  differences  in  the  student  learning  outcomes  and  the effectiveness of the question card-based on TGT learning in the Sub-covalent Bonding material. Using the pre-experimental method of one-group pretest-posttest design, the tenth-grade  students  of  Math  and  Science  Class  of  SMS  Islam  Haruniyah  Pontianak participated in this study. The data collection tools used were learning outcomes tests, observation sheets, and interview sheets. The results of data analysis revealed that the average  pretest  score  was  36  and  the  posttest  was  62.94.  In  addition,  the  t-test statistical  analysis  indicated  a  significance  value  of  0.00  (0.00  <0.05)  which  meanth that there were differences in student learning outcomes between before and after the question  card-based  TGT  learning  model  implemented.  The  gain  value  was  0.42.  In other words, the  question card-based on TGT learning model is effective in improving the student  learning outcomes with good category. Keywords: Covalent Bond, Question Card, Team Games Tournament (TGT)

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