The Design,assembly And Regulation Of Cucurbit[n]uril-based Molecular Switches

Generally,a molecular machine contains two component parts,a mobile macrocycle “wheel” and a long “axle”.The relative positions of these two components may be controlled through chemical,electrochemical or photochemical stimuli.Cucurbit[n]urils(n = 5-8,10,and 14,here after abbreviated as Q[n])are an important class of macrocycles,featuring a relatively rigid hydrophobic cavity and two identical carbonyl laced portals.From the structural point of view,Q[n]s seem excellent macrocycles for constructing molecular switch.In this work,Q[6] and Q[7] was used as the “wheel” to construct molecular switch.The binding interactions between the “wheel” and the “axle” were investigated by NMR,cyclic voltammogram,ab initio calculation,and isothermal titration calorimetry techniques.Following is the main contents.In the first chapter,the development history,structural components,control conditions and potential applications of the molecular switch were described systematically.In addition,the main research contents and significance of this paper were also introduced in detail.In the second chapter,we designed and synthesized a special axle guest hexyldimethyl(ferrocenylmethyl)ammonium(1+)bromide.The binding interactions of 1+ and its oxidized form 12+ with Q[7] and Cy6Q[6] were investigated by 1H NMR,cyclic voltammogram,and isothermal titration calorimetry techniques.The experimental data indicate that both hosts Cy6Q[6] and Q[7] can form stable [2]pseudorotaxanes with 1+ in their different redox states.Most importantly,the combination and dissociation of the hosts with the guest as well as the binding location can be controlled by electrochemical means,which develops a special molecular switch and selector.In the third chapter,an axle molecule ‘guest 2' containing one viologen nucleus and two identical p-toluic acid sides was synthesized.The sequential binding of the Q[7] wheels to the ‘guest 2' axle leads to the formation of a molecular shuttle and then a homowheel [3]pseudorotaxane.The [3]pseudorotaxane can reversibly transform to [2]pseudorotaxane by acid-base control.On the other hand,the firstly formed molecular shuttle can also transform to [2]pseudorotaxane dirrectly and reversibly under p H control.As a whole,molecular shuttle and [3]/[2]pseudorotaxanes constructed a p Hcontrolled multiple interconvertible system.In the fourth chapter,four different kinds of symmetrical guest molecules were designed and synthesized.Each guest contains a central 4,4'-bipyridinium aromatic subunit with two identical carboxylic acid(or hydroxyl,methyl and amino group)-terminated,aliphatic N-substituents at both ends.The binding modes between the host and the guest in aqueous solution were regulated through the Cs+ coordination,resulting in a molecular switch controlled by metal ions.At the same time,the effects of carboxyl,hydroxyl,methyl and amine groups on molecular switches were investigated.