Template-controlled synthesis of chiral cyclohexylhemicucurbit[8]uril

<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>

Download Full-text

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

10.26434/chemrxiv.5702437 ◽

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>

Download Full-text

Formation and Trapping of the Thermodynamically Unfavoured Inverted-Hemicucurbit[6]uril

10.26434/chemrxiv.7977566 ◽

2019 ◽

Author(s):

Elena Prigorchenko ◽

Sandra Kaabel ◽

Triin Narva ◽

Anastassia Baškir ◽

Maria Fomitšenko ◽

...

Keyword(s):

Complex Formation ◽

Combinatorial Chemistry ◽

Trifluoroacetic Acid ◽

Chloride Anion ◽

Binding Affinities ◽

Dynamic Covalent Chemistry ◽

Reaction Selectivity ◽

Low Concentration ◽

Dynamic Combinatorial Chemistry ◽

First Time

Amplification of a thermodynamically unfavoured macrocyclic product through the directed shift of the equilibrium between dynamic covalent chemistry library members is difficult to achieve. We show for the first time that during condensation of formaldehyde and <i>cis</i>-<i>N,N'</i>-cyclohexa-1,2-diylurea formation of <i>inverted-cis</i>-cyclohexanohemicucurbit[6]uril (<i>i-cis</i>-cycHC[6]) can be induced at the expense of thermodynamically favoured <i>cis</i>-cyclohexanohemicucurbit[6]uril (<i>cis</i>-cycHC[6]). The formation of <i>i-cis-</i>cycHC[6] is enhanced in low concentration of the templating chloride anion and suppressed in excess of this template. We found that reaction selectivity is governed by the solution-based template-aided dynamic combinatorial chemistry and continuous removal of the formed cycHC[6] macrocycles from the equilibrating solution by precipitation. Notably, the <i>i-cis</i>-cycHC[6] was isolated with 33% yield. Different binding affinities of three diastereomeric <i>i-cis</i>-, <i>cis</i>-cycHC[6] and their chiral isomer (<i>R,R</i>)-cycHC[6] for trifluoroacetic acid demonstrate the influence of macrocycle geometry on complex formation.

Download Full-text