Construction and Function of Two-Dimensional Supramolecular Architectures

Author:Liu Zuo

Supervisor:li ming zuo


Degree Year:2019





Supramolecular chemistry is a highly interdisciplinary scientific field,covering the chemical,physical and biological characteristics of complex species,which is combined and organized by intermolecular(non-covalent)interactions.In the past decades,scientists have constructed a series of supramolecular nanostructures with specific functions from quasi-zero to three-dimensional architectures,including nanorings,nanofibers,nanotubes,nanosheets,cages,vesicles et al.Among these supramolecular nanostructures,two-dimensional supramolecular nanomaterials have attracted more and more attention in the fields of biology,chemistry and materials due to their unique structural characteristics and excellent properties.The rapid development of two-dimensional materials also provides a new perspective for further exploration in science.How to construct and regulate functionalized two-dimensional self-assembled nanostructures has gradually become an attractive topic in supramolecular chemistry.The purpose of this thesis is to study varieties of functional two-dimensional nanomaterials formed by self-assembly of amphiphilic molecules.The amphiphilic molecules formed by aromatic rods and dendritic oligo ether chains are used as building blocks.These amphiphilic molecules self-assembled into two-dimensional nanosheet structures in aqueous solution or in aqueous methanol solution.With these two-dimensional structures as research objects,we have explored the following functions: 1.Recognition of Different Geometric Structures Through Two-Dimensional Porous Heterostructures.We successfully constructed a dynamic two-dimensional porous heterostructure by combining pH-responsive nanotubes with negatively-charged nanosheets.The bent-shaped aromatic segment with a hydrophilic dendrimer grafted at its apex self-assembles into a hexameric macrocycle through π-π interaction in a neutral aqueous solution,and then stacks on top of each other to form hollow tubules.We have characterized the structure by means of transmission electron microscopy,cryotransmission electron microscopy and atomic force microscopy.The pKa of the pyridyl group is 5.8.At low pH,the pyridine is protonated,and the accumulation between the hexameric macrocycles constituting the one-dimensional nanotube becomes loose due to the electrostatic repulsion,and finally the nanotube is cut into internal positive charged nanorings.Secondly,a rod-shaped amphiphilic molecule with a carboxyl group self-assembles in a neutral and weak acid aqueous solution through π-π interaction to form a two-dimensional nanosheet structure with negative surface.Under neutral conditions(pH=7.4),two amphiphilic molecules with different geometrical configurations were self-assembled to form nanotubes and two-dimensional nanosheets,which showed self-sorting behavior.When the pH is lowered to 5.5,the nanotubes formed by the curved amphiphilic molecules are disassembled into a six-membered nanoring and spontaneously dispersed on the surface of negatively-charged nanosheets in a hexagonal lattice arrangement with regular pores.Interestingly,this dynamic two-dimensional porous heterostructure is capable to adsorb guests with a specific geometry from solution by shape recognition,thereby achieving separation of spherical fullerenes from planar coronene.This two-dimensional heterostructure is expected to be an effective filter to separate spherical-planar guest molecules with different geometries.2.Single-Layered Porous Nanosheet as Spontaneous Macrocycle Generator.We designed and synthesized a paired aromatic segment with a hydrophilic dendrimer grafted at its apex self-assembles into a single-layered porous structure in water methanol solution.The nanosheets with hydrophobic cavities encapsulate a linear substrate with nearly perfect uptake,perform clean cyclization and then spontaneously release as a pure macrocycle.The two-dimensional porous structure was characterized by transmission electron microscopy,cryo-transmission electron microscopy and atomic force microscopy.The small-angle scattering and wide-angle scattering were used to demonstrate the molecular packing motion.After captured by nanopores,hydrophobic linear precursors with constrictive conformation in the confined space facilitate efficient cyclization due to the close proximity of the functional ends rather than chain polymerization.And after the ring formation,the hydrodynamic volume of the ring product decreases a lot,which is no longer matched with the pore size and spontaneously release.The two-dimensional porous nanosheet can be recycled as a spontaneous macrocycle generator.The research results provide new insights and ideas for realizing macrocyclization reaction nanomachine.3.The Effects of 2D Synthetic Lipid Rafts on Biological Membrane.Inspired by natural lipid rafts,we successfully prepared two-dimensional lipid rafts by electrostatic interaction for the first time,and achieved the stimulus response to biological membrane.In neutral buffer solution,a rod-shaped molecule self-assembles into flat sheets through π-π interaction and lateral association.The surface is covered by oligo ether chains with carboxylate anion.The fluorescence of the synthetic rafts is turned on due to the aggregation of positively-charged AIE dye on the sheets,facilitating monitoring for the formation of rafts.Concanavalin A(Con A)protein in neutral pH can load hierarchically into the synthetic rafts to provide discrete Con A aggregates with a uniform size ~12 nm.The uniform aggregates of Con A on the synthetic rafts can stimulate Jurkat cell with enhanced efficiency,compared with random-sized aggregates of Con A.This work provides a basis for simulating the transmembrane signal transduction behavior in the plasma membrane.