scholarly journals Glycosyl Exchange of Unactivated Glycosidic Bonds: Suppressing or Embracing Side Reactivity in Catalytic Glycosylations

2021 ◽  
Author(s):  
Joshua Martin ◽  
Girish Sati ◽  
Tanmay Malakar ◽  
Jessica Hatt ◽  
Paul Zimmerman ◽  
...  
Keyword(s):  
Silyl Ether ◽  
Glycosidic Linkage ◽  
Mechanistic Studies ◽  
Catalyst Structure ◽  
Glycosidic Bonds ◽  
Exchange Processes ◽  
Competing Pathways

While developing boron-catalyzed glycosylations using glycosyl fluoride donors and trialkylsilyl ether acceptors, competing pathways involving productive glycosylation or glycosyl exchange were observed. Experimental and computational mechanistic studies suggest a novel mode of reactivity where a dioxolenium ion is a key intermediate that promotes both pathways through addition to either a silyl ether or to the acetal of an existing glycosidic linkage. Modifications in catalyst structure enable either pathway to be favored, and with this understanding, improved multicomponent iterative couplings and glycosyl exchange processes were demonstrated.

scholarly journals Fluoride Migration Catalysis Enables Simple, Stereoselective, and Iterative Glycosylation

2019 ◽  
Author(s):  
Girish Sati ◽  
Joshua Martin ◽  
Yishu Xu ◽  
Tanmay Malakar ◽  
Paul M. Zimmerman ◽  
...  
Keyword(s):  
Room Temperature ◽  
Building Blocks ◽  
Silyl Ether ◽  
One Pot ◽  
Glycoside Synthesis ◽  
Glycosidic Bonds ◽  
Stable Forms

Challenges in the assembly of glycosidic bonds pose a bottleneck in enabling the remarkable promise of advances in the glycosciences. We report a strategy that applies unique features of electrophilic boron catalysts in addressing current limitations of methods in glycoside synthesis. The strategy utilizes glycosyl fluoride donors and silyl ether acceptors while tolerating the Lewis basic environment found in carbohydrates. The method allows a simple setup at room temperature while utilizing catalyst loadings as low as 0.5 mol %, and air- and moisture stable forms of the catalyst are found to be effective. These characteristics enable a wide array of glycosylation patterns to be accessed, including all four C1-C2 stereorelationships, and the method allows one-pot, iterative glycosylations to generate oligosaccharides directly from monosaccharide building blocks.<br>

Controlled Growth of Imine-Linked Two-Dimensional Covalent Organic Framework Nanoparticles

2019 ◽  
Author(s):  
Rebecca Li ◽  
Nathan C. Flanders ◽  
Austin Evans ◽  
Woojung Ji ◽  
Ioannina Castano ◽  
...  
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Particle Growth ◽  
Emergent Properties ◽  
Mechanistic Studies ◽  
X Ray ◽  
X Ray Scattering ◽  
Exchange Processes ◽  
And Control

Covalent organic frameworks (COFs) consist of monomers arranged in predictable structures with emergent properties. However, improved crystallinity, porosity, and solution processability remain major challenges. To this end, colloidal COF nanoparticles are useful for mechanistic studies of nucleation and growth and enable advanced spectroscopy and solution processing of thin films. Here we present a general approach to synthesize imine-linked 2D COF nanoparticles and control their size by favoring imine polymerization while preventing the nucleation of new particles. The method yields uniform, crystalline, and high-surface-area particles and is applicable to several imine-linked COFs. In situ X-ray scattering experiments reveal the nucleation of amorphous polymers, which crystallize via imine exchange processes during and after particle growth, consistent with previous mechanistic studies of imine-linked COF powders. The separation of particle formation and growth processes offers control of particle size and may enable further improvements in crystallinity in the future.

scholarly journals Fluoride Migration Catalysis Enables Simple, Stereoselective, and Iterative Glycosylation

2019 ◽  
Author(s):  
Girish Sati ◽  
Joshua Martin ◽  
Yishu Xu ◽  
Tanmay Malakar ◽  
Paul M. Zimmerman ◽  
...  
Keyword(s):  
Room Temperature ◽  
Building Blocks ◽  
Silyl Ether ◽  
One Pot ◽  
Glycoside Synthesis ◽  
Glycosidic Bonds ◽  
Stable Forms

Challenges in the assembly of glycosidic bonds pose a bottleneck in enabling the remarkable promise of advances in the glycosciences. We report a strategy that applies unique features of electrophilic boron catalysts in addressing current limitations of methods in glycoside synthesis. The strategy utilizes glycosyl fluoride donors and silyl ether acceptors while tolerating the Lewis basic environment found in carbohydrates. The method allows a simple setup at room temperature while utilizing catalyst loadings as low as 0.5 mol %, and air- and moisture stable forms of the catalyst are found to be effective. These characteristics enable a wide array of glycosylation patterns to be accessed, including all four C1-C2 stereorelationships, and the method allows one-pot, iterative glycosylations to generate oligosaccharides directly from monosaccharide building blocks.<br>

Controlled Growth of Imine-Linked Two-Dimensional Covalent Organic Framework Nanoparticles

2019 ◽  
Author(s):  
Rebecca Li ◽  
Nathan C. Flanders ◽  
Austin Evans ◽  
Woojung Ji ◽  
Ioannina Castano ◽  
...  
Keyword(s):  
High Surface ◽  
High Surface Area ◽  
Particle Growth ◽  
Emergent Properties ◽  
Mechanistic Studies ◽  
X Ray ◽  
X Ray Scattering ◽  
Exchange Processes ◽  
And Control

Covalent organic frameworks (COFs) consist of monomers arranged in predictable structures with emergent properties. However, improved crystallinity, porosity, and solution processability remain major challenges. To this end, colloidal COF nanoparticles are useful for mechanistic studies of nucleation and growth and enable advanced spectroscopy and solution processing of thin films. Here we present a general approach to synthesize imine-linked 2D COF nanoparticles and control their size by favoring imine polymerization while preventing the nucleation of new particles. The method yields uniform, crystalline, and high-surface-area particles and is applicable to several imine-linked COFs. In situ X-ray scattering experiments reveal the nucleation of amorphous polymers, which crystallize via imine exchange processes during and after particle growth, consistent with previous mechanistic studies of imine-linked COF powders. The separation of particle formation and growth processes offers control of particle size and may enable further improvements in crystallinity in the future.

Social exchange processes, health behaviour, and health behaviour change

2008 ◽  
Vol 16 (3) ◽  
pp. 131-134
Author(s):  
Urte Scholz ◽  
Rainer Hornung
Keyword(s):  
Social Exchange ◽  
Health Behaviour ◽  
Psychological Research ◽  
Smoking Behaviour ◽  
Self Report ◽  
Long Term Effects ◽  
Main Research ◽  
Research Areas ◽  
Exchange Processes ◽  
Multi Method Approach

Abstract. The main research areas of the Social and Health Psychology group at the Department of Psychology at the University of Zurich, Switzerland, are introduced. Exemplarily, three currently ongoing projects are described. The project ”Dyadic exchange processes in couples facing dementia” examines social exchanges in couples with the husband suffering from dementia and is based on Equity Theory. This project applies a multi-method approach by combining self-report with observational data. The ”Swiss Tobacco Monitoring System” (TMS) is a representative survey on smoking behaviour in Switzerland. Besides its survey character, the Swiss TMS also allows for testing psychological research questions on smoking with a representative sample. The project, ”Theory-based planning interventions for changing nutrition behaviour in overweight individuals”, elaborates on the concept of planning. More specifically, it is tested whether there is a critical amount of repetitions of a planning intervention (e.g., three or nine times) in order to ensure long-term effects.

PHOTONS SHEDDING LIGHT UPON CHARGE EXCHANGE PROCESSES IN COLLISIONS OF 24 keV O3+ WITH ATOMIC HYDROGEN

1989 ◽  
Vol 50 (C1) ◽  
pp. C1-349-C1-352
Author(s):  
R. HOEKSTRA ◽  
K. BOORSMA ◽  
F. J . de HEER ◽  
R. MORGENSTERN
Keyword(s):  
Charge Exchange ◽  
Atomic Hydrogen ◽  
Exchange Processes
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