Mechanism Study Of Host-Guest Based Molecular Assembly Systems

Host-guest chemistry is an important part of supramolecular chemistry.Normally,macrocyclic molecule based host-guest chemistry can be considered as a process that the macrocyclic host molecules with certain cavities recognize guest molecules with suitable structural size specifically to form host-guest complexes.Benefited from their dynamic reversibility and stimuli responsive property,host-guest based molecular assembly systems have been widely used in many fields such as catalysis,smart material and medical treatment.However,these studies are mainly focused on the innovation of structures and functionalities,corresponding detailed assembly mechanisms are often lacking.Revealing the kinetic and thermodynamic mechanisms can provide a better understanding of the assembly processes,which will contribute to further designs of more assembly systems with better functionality and controllability.In this thesis,two host-guest based molecular assembly systems were taken as model systems to show that a systematic study on the thermodynamic and kinetic mechanisms can provide rational designs to regulate the kinetics of host-guest system.The main contents are as follows:1.The kinetics of a cucurbit[7]uril based pseudorotaxane system was investigated.Firstly,pseudorotaxane PRA was prepared with CB[7]and β-CD as hosts as well as viologen derivatives as guest.The addition of competitive guest gave pseudorotaxane PRB as the finally product after a thermodynamicdriven host-guest exchange process.The kinetics of the host-guest exchange process was characterized systematically by micro-fluidic nuclear magnetic resonance spectroscopy.The results showed that the dissociations of CB[7]MV and β-CD-ADA complexes had decisive importance on the kinetic orders,and the steric groups would have great impact on the assembly rate constants.2.The thermodynamic and kinetic mechanisms of a cyclodextrin based selfsorting system was studied.We constructed a four components self-sorting system using β-cyclodextrin γ-cyclodextrin as host,and two kinds of pyrene derivatives as guest.The structures of the four host-guest complexes in this system were well characterized via nuclear magnetic resonance spectroscopy and isothermal titration calorimetry.The results showed that a new kind of 2:2 host-guest complex named TBAPYS2@y-CD2 was formed.In addidtion,the thermodynamics and kinetics were also characterized by isothermal titration calorimetry experiments and stopped-flow fluorescence experiments,respectively.These results showed that the formation of TBAPYS2@y-CD2 served as the driving force and rate-determined step of the self-sorting process.3.A solid-liquid interface molecular assembly system was constructed by the pseudorotaxane studied in the first part and gold nanoparticles.We characterized the aggregation behaviors of the gold nanoparticles under the assistance of viologens with different side chains by UV-visible spectroscopy,Zeta potential and surface-enhanced Raman spectroscopy.The results showed that the aggregation of gold nanoparticles was driven by van der Waals force,hydrophobic interactions and electrostatic interactions cooperatively.At the same time,we also found that the introduction of CB[7]and β-CD can regulate the assembly behavior of viologen derivatives on the surface of gold nanoparticles by forming host-guest complexes with viologens.