Construction Of Supramolecular Structures Based On Inclusion Of Cyclodextrins And Ionic Self-Assembly

In supramolecular chemistry,the main study is about the fabrication of some ordered molecular aggregates with special structures or functions using weakly intermolecular interactions or their cooperative ones between two or several molecules, such as hydrogen bonding,van der Waals forces,electrostatic interactions,dipole-dipole interactions,host-guest interactions,coordinative metal binding,Ï€-Ï€stacking, amphiphilic association,etc.This dissertation is focused on the design and assembly of some novel ordered aggregates based on the inclusion of cyclodextrins and ionic self-assembly strategies,and a new attempt about "noncovalent amphiphiles" was also done.There are three main experimental studies in this dissertation as following.1.The fabrication of polypseudorotaxanes withβ-cyclodextrins(β-CD) and copolymer F127.Based on the experimental results,two researches were attempted:the supramolecular self-assembly of polypseudorotaxanes in ionic liquid bmimPF₆ and the differences from the normal systems;the assembly of supramolecular hydrogel hybrid by the introduction of gold nanoparticles.Following results are obtained.(1) The polypseudorotaxanes have been synthesized in the mixture of ionic liquid and ethanol when the blocks of PEO-PPO-PEO triblock copolymers are recognized and included byβ-CD to form the crystalline inclusion complexes.XRD and solid-state ¹³C CP/MAS NMR studies show that the inclusion complex domains of the polypseudorotaxanes take channel-type structures,andβ-CD molecules in the polypseudorotaxanes adopt a symmetrical conformation due to the formation of the inclusion complexes.It is surprising that not only the PO segments but also many EO segments are included byβ-CD molecules in theβ-CD/F127 polypseudorotaxanes through combination of the DSC and ¹H NMR studies.Considering the similar total complexation energy betweenβ-CD-PEO andβ-CD-PPO,it is much possible forβ-CDs to include PEO blocks in some special conditions.It is also much interested that the competition between F127 and bmimPF6 to determine which one will be included may be controlled by the quantity of ethanol aroundβ-CD/bmimP₆ inclusion complexes. This finding might be important for the new understanding on supramolecular self-assembly in ionic liquids.(2) We have successfully prepared a supramolecular hydrogel containing gold nanoparticles(GNPs) and thio-β-CDs based on both physical and chemical crosslinks, and studied their sol-gel-sol transition.The hydrogel is constructed from a triblock copolymer Pluronic F127(PEO100-PPO70-PEO100),mono-6-thio-β-cyclodextrins, and GNPs.The control experiments indicate that the hydrogel can only be formed by the synergetic interactions between F127,SH-β-CDs,and GNPs,which are all indispensable.According to all the characterization results,SH-β-CDs couple GNPs with their thio- groups and include PPO blocks of F127 to form polypseudorotaxanes. One polymer chain may thread many CDs adsorbed on different GNPs,and meanwhile, different polymer chains may thread CDs adsorbed on the same GNP.Both possibilities may bring about physical crosslinks to give rise to a network structure.This supramolecular hydrogel also exhibits a gel to sol transition by adding a more competitive guest.Considering the biological and pharmaceutical applications of GNPs and CDs,such kind supramolecular hydrogel may be of wider potentials in the near future.2.The preparation and characterization of organic nanostructures based on ionic self-assembly.Some novel ordered nanostructures were fabricated by using the facile ionic self-assembly(ISA) strategy with different substrate molecules(such as small organic molecule:1-adamantanamine chloride and surfactant:sodium deoxycholate monohydrate).Following results are obtained.(1) We employ a facile ISA route,through the complexation between 1-adamantanamine hydrochloride(AdC1) and a double-tailed anionic surfaetant,aerosol AOT,to fabricate the complexes.Their properties and structures are characterized respectively by ¹H NMR,SEM,DSC/TGA,POM,SAXS,WAXD,and UV-visible spectroscopy.The stoichiometry between AOT and Ad in the complexes is determined as a 1:1 molar ratio.AOT-Ad complexes present a hexagonal columnar phase,which is derived from the reverse hexagonal lattice of pure AOT with Ad blocks inside.Ad segments seem to stack sparsely while AOT ones may be tightly overlapped with their alkyl chains interdigitated.Such binary complexes are well crystallized and stable below 200℃.Notably,the aggregates from AOT-Ad complexes result in organic nanobelts with the thickness about 100 nm,which are plastic enough to bend almost to a circle.Such easily fabricated nanobelts with special properties(photoelectric and magnetic) may be used to tailor the parts of nanomachine.Other anionic surfactants may also be used to tune the product morphology.What's more,β-CD could include Ad blocks and form stable supramolecular inclusion complexes,which look like the amphiphiles and are expected to self-assemble into some ordered structures in the water. It is therefore believed that,abundantly functional soft materials could be produced facilely with such supramolecular ISA strategy.(2) We successfully employ a much facile ISA route,through the complexation between 1-naphthylammonium chloride(NA) and sodium deoxycholate(NaDC),to form solid-like vesicles(stable and nearly kept their original morphology as solvent evaporation) spontaneously in aqueous environment,which could then be transformed to nanobelts with increasing temperature.The particular structures are characterized respectively by electron microscopes,spectroscopies,AFM,fluorescence microscope, NMR,etc.In the low temperature system,there were a large number of polydisperse spherical aggregates with their outer diameters at the range of 50-300 nm.Their shells could be clearly noted with the thickness at the range of several to several tens of nanometers.Such a shell thickness was also asymmetric for the same nanosphere,and the thinnest part was only about 2 nm.It was also observed that some nanospheres were interlinked together with the wall fusion to some extent.The formation of vesicular structures was also supported via AFM observation.The ratio of the diameter and height of the nanospheres was estimated to be ca.10,which should indicate the shell collapse. Also,quantum dots and gold nanoparticles were successfully entrapped into these vesicles,which was proved as a effective method for the confirmation of vesicle structures in situations unsuitable for dye probes.In the complexes,theÏ€-Ï€stacking of naphthalene rings resulted in a rigid layered framework,and the deoxycholate blocks of NaDC in complex were more flexible.The steroidal and hydroxyl groups could associate with their neighbors to extended multilayer.Elevated temperature could induce a decrease of the membrane spontaneous curvature,which should be the essential reason for the transformation of spherical vesicles to nanobelts.Therefore, through simply changing different building blocks,we could expediently acquire many unique organic/inorganic nanomaterials with various structures and functions from aqueous environment via ISA strategy,which will exploit the methods to prepare stable organic ordered assemblies.3.Self-assembly vesicles made from a cyclodextrin supramolecular complex.The ternary supramolecular cyclodextrin complex was designed and fabricated by using synthetically inclusion of cyclodextrins and ISA strategies.The amphiphiles-like supramolecular structure was fabricated by using the outer hydrophilicity of cyclodextrins and the noncovalent link of the hydrophobic tails,and assembled to vesicles.Following results are obtained.Self-assembly vesicles have been made from a CD supramolecular complex,which is cooperatively formed with naturalβ-CD,1-naphthylammonium chloride(NA),and AOT via weak noncovalent interactions.In the complex structure,a NA molecule is included inside aβ-CD molecule while it is coupled with an AOT molecule on one side. The supramolecular structure and morphology of the vesicles were characterized by transmission electron microscopy(TEM) and dynamic light scattering(DLS).Using the uranyl acetate as a negative staining agent,we observed the closed spherical vesicles in the systems,with their outer diameters in the range of 30～200 nm.DLS measurements were also performed to measure the average diameters of vesicles.Results obtained are consistent with the ones observed with TEM,showing an average hydrodynamic diameter of about 100 nm.The mechanism of vesicle formation and transition is discussed along with the data of induced circular dichroism spectrum,UV-visible spectroscopy,polarized optical microscopy,and ¹H NMR.Both the fabrication and the transition of vesicles are controlled by the inclusion equilibrium and the cooperative binding of noncovalent interactions,including:"key-lock" principle,electrostatic interaction,Ï€-Ï€stacking,and amphiphilic hydrophobic association.Some non-included or escaped NA molecules still exist and could attract AOT molecules to form complexes. This is a nonreversible process and will eventually break the equilibrium existing during the inclusion formation.In the meantime,some vesicles dissociate and some ones re-assemble.Then,the newly formed NA-AOT complexes are organized through the noncovalent interactions mentioned above.They are oriented in the same direction, forming the flake-like aggregates.The study presented a possibility on the fabrication and assembly of noncovalent amphiphiles,which was one type of flexible and modifiable supramolecular complex between molecules and aggregates.It is therefore expected as one remarkable study thought.Thanks for the supports from the National Natural Science Foundation of China (No.20573066 and 20773080).