Functionalized Supramolecular Self-assemblies Based On Cucurbit[n]uril

Cucurbit[n]uril (CB[n]) is a family of macrocyclic compounds comprising n glycoluril units. The most common and also well-studied numbers are four CB[n] homologues, that is, CB[5], CB[6], CB[7] and CB[8]. As a kind of macrocyclic compounds, CB[n] has a hydrophobic cavity that is accessible through two identical carbony-fringed portals by hydrophobic interaction and charge-dipole interaction between host molecule and guest molecule. Supramolecule chemistry of CB[n] has an amazing development in the last three decades because of the special structure and excellent property of CB [n].An example of applications of cucurbit[n]uril (especially CB[6]) in supramolecule chemistry is construction of (pseudo)rotaxane. The efficient synthesis of mechanically interlocked molecules such as catenanes and rotaxanes have attracted considerable attention arising from not only their aesthetic appeal but also their potential applications such as molecular machines or switches. Rotaxanes based on CB[6] have been successfully employed in the construction of molecular machines. Here, translocation of the ring (CB[6]) along the linear component can be achieved by external chemical stimuli. In appropriately designed systems, such mechanical movements can be made to occur between two different well-defined states, and if such movements are signaled by an observable change in the property of the system, they can behave as switches for sensor and molecular-scale information processing.Another application of cucurbit[n]uril in supramolecule chemistry is construction of supramolecular amphiphiles. In contrast to conventional amphiphiles, supramolecular amphiphiles (SA) are amphiphiles that are formed by non-covalent interactions. One of the advantages of non-covalent interactions is the avoidance of tedious covalent synthesis procedures. SAs of different topologies and functions can be easily fabricated. SAs allow for tuning of their amphiphilicity in a reversible fashion, leading to controlled self-assembly and disassembly. The self-assembly of SAs can also provide opportunities for functional modulation of nanomaterials. Herein, we use cucurbit[n]uril as host to build pH-responsive molecule switch and functionalized supramolecule amphiphile assemblies.1. Reversible pH-controlled switching of an artificial antioxidant selenoenzyme based on pseudorotaxane formation and dissociationCB[6] has been studied extensively to form very stable1:1host-guest complex with diprotonated diaminoalkanes, particularly diaminobutane and diaminopentane. However, when the two nitrogen atoms are monoprotonated or deprotonated, the binding constant with CB[6] decreases significantly. By this way, CB[6] and polyamine can be used to design pseudorotaxane-based pH-responsive molecular switch.Herein, we designed an organoselenium compound as GPx model which contains not only catalytic selenium center but also two imino groups. In the presence of CB[6], the GPx mimic formed1:1host-guest pseudorotaxane complex when pH was below6. In this case, the organoselenium compound did not show GPx activity obviously as the active site was encapsulated into CB[6] and thereby cannot bind substrate. When pH was above7, the binding ability of CB[6] with the organoselenium compound decreased significantly. As a result, with the rise of pH the active site gradually exposed to solution that caused a gradually increased GPx activity. Thus, the designed selenoenzyme model can be switched on/off through the changing of pH at a mild environment (pH between7and6).2. Cucurbit[7]uril-based vesicles formed by self-assembly of supramolecular amphiphilesCB[7] has a good aqueous solubility, which is no possessed by CB[6] and CB[8], and own a hydrophobic at an appropriate size of P-CD. Thus, some of the properties of CB[7] are similar to these of P-CD. For example, CB[7] may be used as a host for drugs.Herein, we developed an effective strategy for the facile preparation of vesicles via multilevel self-assembly of CB[7] and guest molecules based on host-guest interactions and superamphiphile self-assembly. The disassembly of vesicles can be realized by addition of excess1-adamantanamine hydrochloride. The vesicles can act as nanocapsules to encapsulate molecules within their hollow cavities and used as controlled drug delivery carriers due to their disassembly caused by the competitive guest molecule.3. Nano-hydrolase formed by cucurbit[8]uril-based supramolecular amphiphile assembliesCB[8] has a larger hydrophobic cavity than CB[6] and CB[7], so it can accommodate two guest molecules inside the hydrophobic cavity. The typical example is that CB[8], N,N’-dimethyl-4,4’-bipyridinium (MV2+) and2,6-dihydroxynathphalene (HN) can form ternary complex when their components are mixed in a1:1:1ratio. The major driving force for the ternary complex formation appears to be strong charge-transfer (CT) interaction between HN and MV2+inside the host cavity.Herein, we designed a guest molecule which contains a head of MV2+and three hydrophobic alkyl chains. Then we developed an effective strategy for the facile preparation of vesicles via multilevel self-assembly of CB[8] and guest molecules based on host-guest interactions and superamphiphile self-assembly. Because the instantaneous and quantitative formation of an inclusion complex containing a hetero-guest pair can be achieved by addition of1equiv of HN to the1:1complex of MV2+and CB[8], we used another guest molecule which combines naphthalene and imidazole to introduce the hydrolase activity centre onto the surface of vesicles. By this way a nano-hydrolase model was prepared.