Mengfei Ni

Pillar[5]arene-based polymeric architectures constructed by orthogonal supramolecular interactions

Ureidopyrimidinone functionalized pillar[5]arene (UPyP5) was synthesized and employed to complex with a bisparaquat derivative (G) to form supramolecular polymers at relatively high concentration. The orthogonal binding interactions including quadruple hydrogen bonding and host-guest interaction should play vital roles in the construction of this linear assembly.

Dramatically Promoted Swelling of a Hydrogel by Pillar[6]arene–Ferrocene Complexation with Multistimuli Responsiveness

The swelling-shrinking transition of hydrogels is crucial for their wide applications such as actuators and drug delivery. We hereby fabricated a smart hydrogel with ferrocene groups on pendant of polymer networks. While it was immersed in the water-soluble pillar[6]arene (WP6) aqueous solution, the hydrogel was dramatically swollen, which was an approximately 11-fold promotion in weight compared with that in pure water, due to the formation of the inclusion complexes between WP6 and ferrocene groups in the hydrogel. In particular, the well-swollen hydrogel exhibited good responsiveness to multistimuli including temperature, pH, redox, and competitive guests by tuning the dissociation/formation of WP6-ferrocene inclusion complexes or the strength of their charges. Meanwhile, potential application of such a smart hydrogel in pH-responsive drug release was demonstrated as well.

Dynamic self-inclusion behavior of pillar[5]arene-based pseudo[1]rotaxanes

It was found that spontaneous isomerization takes place between three isomers of a pillar[5]arene (P5)-based pseudo[1]rotaxane. The isomerization process could be monitored by (1)H NMR spectra in polar solvent and the geometric configurations of the three isomers were further evaluated by theoretical calculations. In the threaded forms, the alkyl side chain might be preorganized by intramolecular N-HO bonds between the urea group of the side chain and the methoxy group of the P5 and further stabilized by multiple interactions, including H-bonding, C-H∙∙∙π interactions, and the steric effect of the N-Boc moiety. These cooperative interactions greatly enhance the stability of the threaded form in polar solvent, and endow it with very special self-inclusion behavior.

A novel dynamic pseudo[1]rotaxane based on a mono-biotin-functionalized pillar[5]arene

A mono-biotin-functionalized pillar[5]arene P1 was synthesized by the click reaction, which could form a stable pseudo[1]rotaxane P1′ in a non-polar or weak-polar solution. Interestingly, the obtained pseudo[1]rotaxane P1′ exhibited a dynamic slow disassembly process within the NMR timescale upon adding a strong-polar solvent or competitive guest. Moreover, this dynamic behavior also had potential application in aqueous solution, which might be used as a switch to turn on or off the bioactivity of the biotin moiety.

Thermo- and oxidation-responsive supramolecular vesicles constructed from self-assembled pillar[6]arene-ferrocene based amphiphilic supramolecular diblock copolymers

Novel thermo- and oxidation-responsive supramolecular polymeric vesicles in water were constructed from amphiphilic supramolecular diblock copolymers at 37 °C via pillar[6]arene-ferrocene based host–guest interaction, in which the host polymer was pillar[6]arene-terminal-modified poly(N-isopropylacrylamide) (PNIPAM-P[6]) synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization and the guest polymer was ferrocene-terminal-modified methoxy-poly(ethylene glycol) (mPEG-Fc). The host polymer formed micelles in water at 25 °C, and upon addition of guest mPEG-Fc, a hydrophilic supramolecular diblock copolymer PNIPAM-P[6] ⊃ mPEG-Fc was formed, which could become amphiphilic when heated to 37 °C and further self-assembled into supramolecular polymeric vesicles. The resulting vesicles exhibited good thermo- and oxidation-responsiveness, due to the solubility of the host polymer at different temperatures and the oxidation of the ferrocene moiety of the guest polymer, respectively. More importantly, the supramolecular polymeric vesicles could be further applied in the encapsulation of an anticancer drug (doxorubicin hydrochloride) and its controlled release in response to temperature and oxidizing agents.

Chapter 7:Supramolecular Polymers based on Pillararenes

The development of supramolecular polymers has expanded their applications in various fields such as biology, medicine and materials. Among the various types of supramolecular polymer, macrocycle-based supramolecular polymers receive great attention because of their useful properties and applications. Pillararenes are a novel class of macrocycles that have unique structures and host–guest properties. Significantly, pillararenes have been widely used in the construction of various supramolecular systems, especially supramolecular polymers. In this chapter, recent advances in pillararene-based supramolecular polymers are summarized in four sections: the self-assembly of mono-functionalized pillararenes (including self-inclusion complexes, cyclic dimers, and supramolecular polymers); linear supramolecular polymers based on pillararenes; supramolecular polymer networks based on pillararenes; and pillararene-based poly(pseudo)rotaxanes on polymer chains. These outstanding studies are focused on stimuli-responsive polymers, supramolecular gels, molecular devices, and the modification of polymeric materials, which show a bright future for pillararene-based supramolecular polymers.