Anion Recognition By Peptidyl Amidothioureas In Multiple β-Turn Folding Conformations

Anion coordination chemistry is an important research subject of supramolecular chemistry,involving the development of various highly selective recognition,reaction,transportation and regulation processes via intermolecular interaction such as hydrogen bonding.Anions are indispensable species in life system,efficient extraction and separation of anions in solution is particularly important.Design and synthesis of the corresponding anion receptors focus on finding binding receptor units.Inspired by the polypeptide secondary structures,such as α-helix and β-turn,which regulate protein recognition process,β-turn secondary structure is introduced into the anionic ligand to design receptors for anionic guests by weak interaction,such as encapsulation.In this thesis,peptidyl amidothiourea is introduced to build β-turn structure template,three-armed and four-armed peptidyl amidothioureas β-turn folded conformation are designed based on the nitrilotriacetic acid and EDTA structural frameworks.The molecule uses the β-turn folded conformation to arrange the side arms into a cage with an optimal structure,which effectively encapsulates the anionic guest and realizes the recognition of the anionic guest.The disseration consists of three chapters.The first chapter is the preface,focusing on the β-turn structure and its research methods and applications.This is followed by the summary of the research progress of the peptidyl amidothiourea molecule containing β-turn structure.Examples of anionic ligand structures and supramolecular assembly based on anionic coordination chemistry are described.Inspired by research on such neutral receptor structures,it is found that adding hydrogen bonding sites in the host structure can effectively improve the binding ability.Together with the developments of unilateral and bilateral Npeptidyl amidothiourea molecules contains β-turn structures that have been investigated in our group,objectives of this thesis are presented.In the second chapter,a three-arm peptidyl amide-based peptidomimetic supramolecule with β-turn structure was designed and synthesized using nitrotriacetic acid structural template.This molecule takes advantages of the β-turn structure to arrange the side arms into a symmetrical cage in an optimal structure.The anion receptor takes a "claw machine" structure in solution,which binds Cl-,Br-,and I-at a stoichiometry of 1:1.According to the size and shape of anion,we designed receptor molecules containing different amino acid residues,such as Ala,Aib,and Phe,the βturn structure adjusted by the amino acid residue structure so that structures of the molecules are tuned.The receptor molecules were applied for encapsulation of halogen anions.This chapter introduced β-turn structural motifs into design of peptidyl amidothiourea anion receptors,and provides an avenue towards the anion receptors for application of anion recognition.The third chapter is based on the experimental results of the second chapter.The size and shape of the N3AibH anion cage was found to match well those of Cl-.The potential of Aib residue in the "claw-machine" like anion cages is attributed to β-turn structure.It was envisaged that the cavity could be enlarged.On the basis of sacrificing the "size-dependence" binding ability determined by the cavity size,EDTA template is used to design peptidyl amidothiourea molecules with different amino acid residue of Ala,Aib,Phe or Val.The role of formed cavity size and β-turn stability are explored in term of the recognition.