Design And Synthesis Of Pyridyl Cavitands And Their Recognition For Polar Molecules

The selective recognition of hydrophilic molecules in water remains a challenge in supramolecular chemistry.As we all know,nature receptors have good selective recognition for polar molecules in water,which involves the synergistic action of hydrogen bonding with hydrophobic effects.Inspired by this,based on the unique structure of resorcin[4]arenes,we designed and synthesised a series of water-soluble cavitands which contain deep hydrophobic cavities and hydrogen bonding sites.Moreover,we applied them to recognize some polar molecules in water.In this thesis,we will introduce the synthesis and molecular recognition of pyridyl cavitands as the following in three parts:Firstly,we synthesized the water-soluble cavitand 1 by introducing ortho-pyridine groups on the rim of resorcin[4]arene through the condensation reaction of diamine and aldehyde,and the methylimidazole at the feet.Then we studied the behavior of water-soluble cavitand 1 with cycloalkane and hydrophilic molecule 1,4-dioxane.The study shows that:1)Cavitand 1 formed host-guest complexes with cyclic alkanes in water through hydrophobic effects.Due to the limitation of the cavity,it showed good recognition for six-membered and seven-membered rings;2)Cavitand 1 cannot form a stable host-guest complex with1,4-dioxane owing to its high hydrophilicity.Secondly,we synthesized the water-soluble cavitand 2a and 2b by introducing meta-pyridine groups on the rim of resorcin[4]arene through the condensation reaction of diamine and dinitrile,and the methylimidazole or sodium carboxylate at the feet.Furthermore,we explored the ability of 2a and 2b to recognize polar molecules.The study showed that:1)Cavitand 2a and 2b can recognize polar molecules in water.2)Metallo cavitand 2a-2Pd can selectively recognize highly hydrophilic polar molecules in water,such as tetrahydrofuran,1,4-dioxane.That because metal coordination makes the cavitand more rigid,which is favorable for stable host-guest complex formation.Thirdly,water-soluble cavitands 3a and 3b were synthesized as the above same process.Meanwhile,we studied their molecular recognition.The research shows that:1)Cavitands 3a and 3b can selectively recognize polar molecules such as tetrahydrofuran and 1,4-dioxane in water.At the same time,the ITC experiment shows that the cavitand 3a retains a high affinity for polar molecules.For example,the complex constant Ka of the host to 1,4-dioxane is 1.09×10⁴ M^-1.In addition,quantum chemical calculations elucidated the water-mediated hydrogen bonding patterns responsible for the binding.2)Cavitand 3a can recognize water pollutants chloroform and PFOA with high sensitivity.When it formed complex with the water pollutant molecule,the fluorescence spectrum shows obvious fluorescence enhancement;3)The metallo cavitand 3a has selective recognition for o-xylene between its isomers and also can be used for the separation of o-xylene between its isomers.