The Investigation Of Pillararenes-Based Host-Guest Chemistry And Its Application

Macrocycles chemistry is an important subclass of supramolecular chemistry,which attracted considerable attention from the scientific community.Supramolecular chemists design and develop four representative generations of macrocyclic molecules,which are crown ethers,cyclodextrins,calixarenes and cucurbiturils.Pillararenes,known as fifth generation of macrocyclic molecules,induced an intense of research and development in supramolecular chemistry.To date,pillararenes have showed significant potential in various application areas.This dissertation is mainly about host-guest molecular recognition based on pillararenes and their related applications.In the first part,a novel pillararene-indicator system between anionic water-soluble pillar[6]arene(WP6)and an aromatic fluorescent dye acridine orange(AO)was constructed.Upon complexation with electron-rich cavity of WP6,AO showed fluorescence quenching and color change due to the host-guest charge-transfer interactions.The established pillararene-indicator system was further employed in the detection of choline compounds and monitoring enzymatic reactions.In the second part,we designed a turn-on fluorescence switch based on host-guest complexation between a pH-sensitive dye(salicylaldehyde)and a water-soluble cationic pillar[5]arene(AP5).Salicylaldehyde is weakly fluorescent in its neutral form(SA),but exhibits strong fluorescence in its deprotonated form(SA-).When AP5 was added to a solution of salicylaldehyde at neutral pH,the transformation from SA to SA-occurred due to the different association constants between AP5(?)SA and AP5(?)SA-.The complexation-assisted dye deprotonation and deaggregation effects caused a pronounced fluorescence enhancement of the solution.We further employed this turn-on fluorescence switch for FID detection of phenolic contaminants,including chlorophenols.In the third part,we design a novel host-guest recognition motif on the basis of anionic water-soluble pillar[6]arene(WP6)and a class of photosensitizer,methylene blue(MB),which can be further used to construct a supramolecular ROS switch.When guest MB complexed with the host,the ROS generation of MB was inhibited.After the addition of competitive guest hexamethylenediamine dihydrochloride(G),the ROS generation ability of MB recovered because G can drive MB out of the cavity of the host by virtue of its higher binding ability with the host.Upon establishment of this supramolecular ROS switch,the relevant application in antibacterial was conducted.This work offers a new way to the field of targeted therapy and antibacterial.In the fourth part,a difunctional pillar[5]arene(H)bearing two carboxyl units was employed as a macrocyclic host to investigate the host-guest complexation with various amine-based guests(G1-G6)both in solution and in the solid state by using 1H NMR,isothermal titration calorimetric(ITC),2D NOESY and X-ray crystallographic analysis.This host-guest recognition motif can be further employed in the fabrication of robust suparmolecular structures including rotaxanes and catenanes.