Study Of Establishing An Anion-coordination-based A₄L₆ And Multi-stimuli Behavior

By precisely controlling the interconversion between differently sized and shaped conformations,proteins,are capable of switching their functions OFF/ON in response to exterior triggers.Supramolecular assemblies that are held together by dynamic noncovalent interactions provide the possibility to mimic stimuli-responsive behaviors of proteins.In the past decades,supramolecular transformations triggered by template,solvent,concentration,light,component and post-modification have been extensively studied.These studies have significantly contributed to the understanding of the mechanisms of various structural transformations and their applications in such areas as catalysis,smart materials,and guest binding.To enable supramolecular transformations with associated host-guest chemistry,searching for suitable self-assembly systems are desired.To this end,anion coordination,which uses hydrogen bonds instead of the classical metal-ligandcoordinate bonds,has proven a very promising approach to supramolecular architectures.In our recent work,selective encapsulation of biomolecules（e.g.choline）or highly reactive species（P4）was achieved by an A₂L₃（A = anion,L =ligand）triple helicate cage or A4L4 face-based tetrahedral cages.Though these assemblies displayed instant assembling/disassembling behaviors under mild conditions,no supramolecular transformations have been observed yet.It is known that the M4L6（M =metal）tetrahedral cages may experience interconversion with the M2L3 triple helicates under certain conditions.Therefore,we devoted our efforts to explore new assemblies with transformable conformations upon stimuli.In this paper,we devoted our efforts to explore an unusual peripherally templated A₄L₆（“A” denotes anion and “L” is ligand）tetrahedral cage and the reversible interconversion with the A₂L₃ triple helicate in response to multi-stimuli,with accompanying guest capture and release,including three chapters:The first part,we summarized the origin and development of supramolecular assemblies and metal-assembly cage,literatures in urea-or thiourea-based anion receptors,which providing the source of the subject.Finally,we set the aim and meaning of this dissertation.The second part,we designed and sythesized a linear bis-bis（urea）ligand L,which coordinated with phosphate ions（PO43-）to form either A₄L₆ tetrahedral cage（T）or A₂L₃ triple helicate（H）when we used different counter cations of phosphate.By means of HRMS,single crystal structure the conformations were also confirmed.Subsequently we studied on the reversible transformation of the A₄L₆ tetrahedron to the A₂L₃ helicate triggered by concentration,template and solvent.The last part,based on the previous work,peripheral effect was utilized to assemble an“empty” A₄L₆ cage that allows the multi-stimuli-controlled capture/release of biologically important species such as choline and acetylcholine.