Study On The Self-assembly And Properties Of Citrulline Rotaxane Controlled By PH

Cucurbit[n]uril is a new type of macrocyclic hosts.Its rigid hydrophobic cavity and hydrophilic portal make them attracted much attention in supramolecular chemistry because of their superior molecular recognition properties in aqueous media.Rotaxane and pseudorotaxane are the popular research topic in cucurbituril based self-assembly.Generally,such self-assembly often affected by the solvent environment,such as temperature,pH and so on,so,the construction of acid-base molecular machine is an important research topic.Based on the literature reports and our previous studies,a series of long-chain appended bipyridinium derivatives were designed and synthesized.UV-vis absorption spectroscopy,fluorescence emission spectroscopy,isothermal calorimetry and nuclear magnetic resonance techniques were used to characterized the host-guest interaction properties of cucurbit[8]uril(Q[8])and symmetrical tetramethyl cucurbit[6]uril with the guests:1.To investigate the interaction between Q[8] and TMeQ[6] and the guests G1,G2 and G3 which containing a 4,4'-bipyridyl group.The results show that under acidic conditions,Q[8] and the guest G1 and G2 can form a 1:1 supramolecular self-assembly([2]pseudorotaxane),increasing the pH values of the system,Q[8] host can shuttle on G1;1:1 and 2: 1 complex modes can be formed between Q[8] and guest G3,and which can be swhiched by the pH values;TMeQ[6] was mainly located on the carboxylic acid chain of the guest due to the small size of the cavity and can not effect by pH.2.To investigate the interaction between Q[8] and TMeQ[6] and the guests G4,G5 and G6 which containing two 4,4'-bipyridyl groups.The results show that under acidic conditions,Q[8] and the guest G4 can form a 2:1 supramolecular self-assembled([3]pseudorotaxane),and the Q[8] host can shuttle freely on the G4 with the increased pH values;Q[8] and the guest G5 can form 1:1 and 2:1 complexation modes,increasing pH values,Q[8] can slide into the intermediate alkyl chain of the guest G5;Q[8] and the guest G6 can form 2:1 complex,and G6 due to the chain is longer,the Q[8] mainly slides between the alkyl chain,which can not be swhiched by pH values;TMeQ[6] was mainly located on the carboxylic acid chain of the guest due to the small size of the cavity and can not effect by pH.3.The interactions of phenylpyridine derivatives G7,G8 and G9 with Q[8] and TMeQ[6] were investigated.The results show that under acidic conditions,Q[8] and the guest G7 and G8 can form 1:1 complex,which can not be swhiched by pH values.two modes of supramolecular self-assembly,1:1 and 2:1 can be formed between Q[8] and the guest G9,which can be swhiched by pH values.TMeQ[6] was mainly located on the carboxylic acid chain of the guest due to the small size of the cavity and can not effect by pH.