| The development of supramolecular chemistry accompanys with the study of macrocyclic hosts.Therefore,the discovery of novel macrocyclic hosts with fascinating structures and properties has greatly promoted the development of supramolecular chemistry.It is clear that the arrival of crown ethers in 1960s triggered an intense period of research and development in the field of supramolecular chemistry.Four generations of macrocyclic molecules have been investigated by now.They are crown ethers,cyclodextrins,calixarenes and cucurbiturils.They have been applied in a variety of areas,including molecular recognition,nanotechnology,fluorescent chemosensors,drug delivery systems and supramolecular polymers.In 2008,a new class of pillar-shaped macrocyclic hosts has been reported,which is known as "pillar[n]arene".Till now,pillar[n]arenes have played an important role in supramolecular chemistry because of their special structure and excellent host-guest properties.This dissertation is mainly about the host-guest properties between pillar[5]arenes and probes,self-assembly systems and molecular recognition.In the first part,we design and synthesize a novel C02-responsive pillar[5]arene.It self-assembled into micelles and toroid-like structures in water after the treatment of HCL and Co2,respectively.Compared with pH-stimuli,CO2 has advantages such as its non-pollution to environment and its biocompatibility.These controllable well-defined self-assemblies might have potential applications in the fields of controlled release,drug delivery,biomaterials and so on.In the second part,we have successfully constructed a CO2-responsive molecular recognition motif from a tertiary amine modified pillar[5]arene and SDS in water.SDS threaded into the cavity of this pillar[5]arene upon bubbling with CO2 and threaded out upon bubbling with N2 or heating the solution.The inclusion complex acted as a supramolecular amphiphile and self-assembled into spherical vesicles which were disrupted upon bubbling with N2 along with elimination of the inclusion complex.Moreover,the addition of excess SDS also led to the collapse of vesicles due to anion exchange of dodecyl sulfonate groups with bicarbonate anions.The assembly and disassembly of vesicles were successfully employed in gas and surfactant controlled releases of calcein.This new CO2-responsive molecular recognition motif and self-assembly systems based on it have potential use in drug delivery and sensors and should be beneficial for us to better understand biological processes.In the third part,we have developed a terpyridine-based low molecular weight ligand 4.1 which can form hydrogel under slightly acidic conditions only in the presence of divalent copper ions(and chloride).However,other divalent metal ions could not induce the gelation.The microscopy investigations revealed that the gel structure consists of a thin fibrous(about 10 nm in diameter)network.The metallohydrogel exhibited multiple responsivenesses towards gel-to-sol transitions including thixotropy,temperature,and addition of alkali or sodium L-ascorbate.More interestingly,WPS could form a stable host-guest complex with 4.2,resulting in the gel-to-sol transition in macroscopic dimension and leading to the nanofiber-to-vesicle transformation at the nanoscale.These findings may have potential applications in biologically relevant fields and contribute to the investigations in rationalizing the course of aggregation.In the fourth part,we have investigated the adsorptive properties of two easily-obtained pillar[n]arenes,EtP5 and EtP6,towards St and EB.EtP6 was found to be a much better absorbent for both St and EB,and either crystalline or amorphous EtP6 can selectively capture St from a St-EB mixture.This selectivity arises from the guest-induced selective structural change of EtP6 rather than the suitable cavity size.Compared with other small molecule organic separation materials,such as intrinsically porous cage compounds,23 the separation process for EtP6 is closer to a crystallization separation,rather than an adsorptive separation.While the separation of St and EB has been achieved in porous extended frameworks,such as MOFs,this new molecular approach offers potential advantages.For example,EtP6 is soluble,is easy to synthesize,and has better chemical stability than many crystalline MOFs and COFs.While the overall uptake capacity in EtP6 is relatively low compared with porous extended frameworks,and the uptake kinetics are relatively slow,St can be separated with high purity in just one cycle,which is highly desirable.Future work will attempt to increase the uptake capacity and adsorption kinetics without losing the remarkable selectivity,for example by co-crystallization of two or three different pillar[n]arenes.Other hydrocarbon separations,such as the separation of xylene isomers,are also under investigation.In the fifth part,we have investigated the shape selective properties of two easily-obtained pillar[n]arenes,EtP5 and EtP6,towards three xylene isomers.EtP6 was found to have the ability capture pX from a xylene isomer mixture.This selectivity arises from the suitable cavity size as well as the guest-induced selective structural change of EtP6.This is closer to the separation using flexible MOFs and a bit different from our previous reported styrene separation,where the cavity of pillar[n]arenes did not play a role in the process.While the separation of xylene isomers has been achieved in porous extended frameworks,such as MOFs,this new molecular approach offers potential advantages.For example,EtP6 is soluble,is easy to synthesize,and has better chemical stability than many crystalline MOFs and COFs.While the overall uptake capacity in EtP6 is relatively low compared with porous extended frameworks,and the uptake kinetics are relatively slow,pX can be separated with high purity in just one cycle,which is highly desirable.Most importantly,we demonstrated that pillar[6]arene might be used as a versatile material to separate aromatic hydrocarbons due their superb performance in not only styrene purification but also xylene separation.Though pillar[5]arene does not work well in xylene and styrene separation,it may still have the potential to separate other type of hydrocarbons,which remains unexplored.Hydrocarbon separation using higher members of pillar[n]arenes(n = 7,8,9,10)will also be investigated in the near future. |
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