3 research outputs found
Modulating Supramolecular Chirality in Alanine Derived Assemblies by Multiple External Stimuli
Having control over
the supramolecular chirality through multiexternal
stimulators provides many possibilities in realizing functional chiral
materials. Herein, the supramolecular chirality of nanotwists comprising
PA centered with 1,4-phenyldicarboxamide bearing two l/d-helicogenic alanine motifs and achiral COOH at each terminus
of the alanine arms is modulated by solvent, temperature, and ultrasound.
The modulations are mainly due to the hydrogen bonds among gelators
and solvent–gelator interactions, resulting in changes of the
molecular arrangement and subsequent self-assembled nanostructures.
Typically, the gel of PA in ethyl acetate prepared by ultrasonication
method exhibits thixotropic property due to the participation of ethyl
acetate in the self-assembly process, resulting in relatively flexible
and tolerant networks. This study provides a simplistic way to control
the handedness of chiral nanostructures and a rational design of the
self-assembly system with multistimuli-responsive supramolecular chirality
Chiral Covalent Organic Cages: Structural Isomerism and Enantioselective Catalysis
Covalent organic cages are a prominent class of discrete
porous
architectures; however, their structural isomerism remains relatively
unexplored. Here, we demonstrate the structural isomerism of chiral
covalent organic cages that renders distinct enantioselective catalytic
properties. Imine condensations of tetra-topic 5,10-di(3,5-diformylphenyl)-5,10-dihydrophenazine
and ditopic 1,2-cyclohexanediamine produce two chiral [4 + 8] organic
cage isomers with totally different topologies and geometries that
depend on the orientations of four tetraaldehyde units with respect
to each other. One isomer (PN-1) has an unprecedented
Johnson-type J26 structure, whereas another (PN-2) adopts
a tetragonal prismatic structure. After the reduction of the imine
linkages, the cages are transformed into two amine bond-linked isomers PN-1R and PN-2R. After binding to Ni(II) ions,
both can serve as efficient catalysts for asymmetric Michael additions,
whereas PN-2R affords obviously higher enantioselectivity
and reactivity than PN-1R presumably because of its large
cavity and open windows that can concentrate reactants for the reactions.
Density-functional theory (DFT) calculations further confirm that
the enantioselective catalytic performance varies depending on the
isomer