Construction Of Artificial Ion Channels Regulated By 2,2’-bipyridine Ligand

Supramolecular chemistry is an emerging discipline developed in recent years.Pillararenes chemistry and cyclodextrin chemistry are two important research fields of supramolecular chemistry.Pillararene is a new type of macrocyclic host molecule formed by benzene dimethyl ether bridged by methylene,as a cylindrical rigid skeleton in space structure.The pillar[5]arene is a columnar structure of a regular pentagonal straight cylindrical cavity formed by five terephthalate repeating units,with a cavity diameter of about 4.7 （?）.Cyclodextrin（CD）is another type of macrocyclic host molecule with a cone-shaped hollow ring structure formed by multiple glucose units and has a hydrophobic cavity.The cavity diameter ofα-cyclodextrin is also 4.7 （?）,which is basically the same as the molecular inner diameter of pillar[5]arene.Because of its unique structural characteristics,it is conducive to the construction of single-molecule tubular channel structures,thus becoming a useful framework for constructing synthetic channels.Here,we describe the design and synthesis of monomolecular tubular channels based on pillar[5]arene andα-cyclodextrin.2,2’-Bipyridine（Bipy）is a bidentate chelating ligand that can form complexes with many transition metals.It usually has two isomers,cis and trans.A common method to switch between the two conformations is to coordinate Bipy with a suitable metal ion.Two nitrogen atoms of the pyridyl are involved in the coordination to form a stable chelate.The aryl groups are also arranged in these complexes in an almost coplanar manner.Therefore,the conformation of the receptor can be controlled by adding or removing metal ions,thereby realizing an allosteric control.Here we use 2,2’-bipyridinedicarboxylic acid as the organic ligand,and regulate the structure of the tubular channel by adding metal ions.The work of this paper mainly includes the following two parts:In the first part of our work,we connected pillar[5]arene and 2,2’-bipyridine through the demethylation,chlorination and esterification to form two monomolecules with bipyridine in the middle and pillar[5]arene at the both ends.For enhancing their hydrophilicity,we can remove the methyl group of the pillar[5]arene to form compond 2-8 and 2-9.The monomolecular structure formed by the trans-dicarboxylic acids（the carboxyl group is on the opposite side）is a non-tubular structure.And by the coordination of metal ions the non-tubular structure can be turn to a tubular structure.The monomolecular channel formed by cis-dicarboxylic acid（carboxyl group on the same side）is a tubular structure,which can be turning to a non-tubular structure through the coordination of metal ions.We have verified the metal coordination and its regulated conformation flip phenomenon through mass spectrometry,nuclear magnetic titration experiments,two-dimensional spectroscopy,ultraviolet and fluorescence experiments.In the second part of our work,we took α-cyclodextrin as the skeleton,and connected α-cyclodextrin and 2,2’-bipyridine by functionalizition of cyclodextrin,chlorination and esterification of carboxylic acid to form two monomolecules with bipyridine in the middle and α-cyclodextrin at the both ends.A class of monomolecular tubes based on cyclodextrin-2,2’-bipyridine hybrid molecules was constructed.