The Assembly And Modulation Of G-quadruplex And Other Supramolecular Structures

With the rapid development of nanoscience and supramolecular science,self-assembly has become an important method to prepare new materials.Specifically,biomolecules with intrinsic biocompatibility and biodegradability are excellent building blocks for self-assembly.The gels formed by self-assembly is characterized by multiple stimulate responses,thus showing potential applications in varieties of fields,such as biomedicine,nanotechnology and environmental science.Polymers are also important building blocks and behave different from low molecular mass molecules.Herein,we focus on the self-assembly mechanism,fundamental structure-property relationship,as well as the transition and modulation of supramolecular structure.The interface is employed to construct various aggregates.To study the self-assembly behavior,the structures of building blocks are functionalized in different ways including covalent,dynamic covalent and non-covalent binding.The factors affecting the self-assembly process are elucidated by varying cation types,molecular compositions and concentrations.This dissertation includes four parts as following:1.the amphiphilic derivatives of L-histidine with different alkyl chains,NIPCA,UIPCA,and TIPCA,were designed and their self-assembly behaviors with citric acid were investigated.All L-histidine derivatives can form hydrogels with citric acid,and exhibit the decreasing gelation ability and mechanical strength with the increasing chain length.The gelation ability is considered to be affected by the synergistic effect of electrostatic interaction,hydrogen bonding and hydrophobic interaction.The hydrogels exhibit excellent releasing selectivity for charged dyes in aqueous solution,enlightening people to utilize this kind of hydrogels as intelligent carriers to separate the mixtures of charged dyes.2.the effects of different metal ions and their concentrations on stacking modes of G-quartets are elucidated.Monovalent cations(typically K+)facilitate the formation of G-quadruplex hydrogels with both heteropolar and homopolar stacking modes,showing weak mechanical strength.In contrast,divalent metal ions(Ca2+,Sr2+and Ba2+)at given concentrations can control G-quartets stacking modes and increase the mechanical rigidity of the resulting hydrogels through ionic bridge effects between divalent ions and borate.We show that for Ca2+and Ba2+at suitable concentrations,the assembly of G-quadruplexes results in the establishment of a mesoscopic chirality of the fibrils with a regular left-handed twist.Finally,we report the discovery of nematic tactoids self-assembled from G-quadruplex fibrils characterized by homeotropic fibril alignment with respect to the interface.We use the Frank-Oseen elastic energy and the Rapini-Papoular anisotropic surface energy to rationalize two different configurations of the tactoids.These results deepen our understanding of G-quadruplex structures and G-quadruplex fibrils,paving the way for their use in self-assembly and biomaterials.3.a novel strategy to construct G-quadruplex with the promotion of cationic surfactants,such as CTAB,is presented.The hydrophobicity of alkyl chains of CTAB molecules is confirmed to be the dominating factor for the resulting G-quadruplex gels.The structure-property relationships of G-quadruplex gels are carefully characterized by rheology and water content.We use the MacKintosh's theory to rationalize the increase of the gel elasticity dependent on the water content.Importantly,the transition of G-quadruplex structures could be easily realized by modulating the amount of CTAB,accompanying with the phase transition from gel/sol biphase to homogeneous sol phase,as well as the morphology changes.We believe this work will advance our understanding of the construction and modulation of G-quadruplex structures.4.a novel liquid/liquid interface-mediated self-assembly behavior of block copolymer is reported.An aqueous solution of HAuCl4 and a chloroform solution of poly(2-vinylpyridine)-block-polycaprolactone(P2VP199-b-PCL22)are employed as the upper phase and the bottom phase,respectively.Structural transitions from toroids and plate like structures to vesicles and large compound vesicles are observed in the bottom phase by using transmission electron microscopy(TEM).It is proved that vesicles and large compound vesicles are formed through adsorption and desorption of copolymers at the liquid/liquid interface,molecular aggregation and microphase separation in the bottom phase due to the amphiphilic property of protonated P2VPi99-b-PCL22.The well-dispersed Au nanoparticles are formed during the self-assembly process and embedded in the bilayers of the vesicles.The concentrations of HAuC14 and P2VPi99-b-PCL22 have an effect on the self-assembly behavior.A unique structure,"pearl necklace",is obtained at higher concentrations.It is found that aggregation shapes are dependent on the compositions of P2VP-b-PCL copolymers,which could be explained by critical packing parameter,p.