Kelong Zhu

Improved complexation of paraquat derivatives by the formation of crown ether-based cryptands

Self-assembly allows the construction of advanced molecular or supramolecular systems from small building blocks. Host-guest recognition, for its self-selectivity, environmental responsiveness and convenient application to complex molecular devices, plays a significant role in self-assembled systems. During this process, the association constant between the host and guest is an important standard to identify the properties of the systems. In order to prepare mechanically interlocked structures and large supramolecular systems efficiently from small molecules based on a host-guest recognition motif, it is necessary to increase host-guest association constants. Crown ether-based cryptands have been designed and prepared to improve the binding of paraquat derivatives. This feature article aims to describe the design and syntheses of crown ether-based cryptand hosts for paraquat derivatives and the application of the cryptand/paraquat recognition motif in the fabrication of threaded structures, molecular switches and supramolecular polymers.

Anion-Controlled Ion-Pair Recognition of Paraquat by a Bis(m-phenylene)-32-crown-10 Derivative Heteroditopic Host

It has been demonstrated that the complexation of the divalent salts of paraquat can be greatly improved (a K(a) increase up to 219 times was observed) by the introduction of ion-pair recognition through use of urea moieties on the crown ether. This improvement is controlled by not only the solvent polarity but also the nature of the anion. Furthermore, it was found that the binding motif for paraquat guest incorporation into the heteroditopic host is anion-controlled in the solid state. The host-guest complex is a pseudorotaxane in the solid state when the two counterions of paraquat are trifluoroacetate anions while it is a taco complex when the two counterions are hexafluorophosphate or chloride anions.

Anion‐Assisted Complexation of Paraquat by Cryptands Based on Bis(m‐phenylene)‐[32]crown‐10

The complexation of tightly ion-paired divalent salts such as paraquat dichloride by cryptands based on crown ethers can be improved by the introduction of ion-pair recognition as a means of also binding the counteranions. A series of diamide-based cryptands derived from bis(m-phenylene)-[32]crown-10 and designed to complex the bipyridinium dication with anion assistance was synthesized. The ion-pair recognition process was fully characterized by (1)H NMR spectroscopy, UV/Vis spectroscopy, electrospray ionization mass spectrometry and single crystal X-ray analysis. (1)H NMR spectroscopy demonstrated that these new heteroditopic cryptand hosts can complex both the positive and negative components of the paraquat dichloride salt. UV/Vis spectroscopy showed that the addition of chloride anion into equimolar solutions of cryptands 3c or 3g with paraquat bis(hexafluorophosphate) salt (2a) improves the binding of the cryptands to the paraquat guest. Electrospray ionization mass spectrometry and single-crystal X-ray analysis confirmed the 1:1 stoichiometries and ion-pair recognition of these cryptand/paraquat complexes. It was found that the cryptand 3g, with 13 atoms and an isophthalamide moiety in the third chain, exhibited the best binding affinity for tightly ion-paired paraquat dichloride (2b), due to the combination of its spatial compatibility and additional anion-binding site.

Improved complexation between dibenzo-24-crown-8 derivatives and dibenzylammonium salts by ion-pair recognition

The introduction of a urea-based anion binding site onto dibenzo-24-crown-8 can enhance the complexation between dibenzo-24-crown-8 derivatives and dibenzylammonium cation by ion-pair recognition.

pH-Responsive Supramolecular Polymerization in Aqueous Media Driven by Electrostatic Attraction-Enhanced Crown Ether-Based Molecular Recognition

All the previously reported supramolecular polymers based on crown ether-based molecular recognition have been prepared in anhydrous organic solvents. This is mainly due to the weakness of crown ether-based molecular recognition in the presence of water. Here we report a linear supramolecular polymer constructed from a heteroditopic monomer in an aqueous medium driven by crown ether-based molecular recognition through the introduction of electrostatic attraction. In addition, the reversible transition between the linear supramolecular polymer and oligomers is achieved by adding acid and base. This study realizes the breakthrough of the solvent for supramolecular polymerization driven by crown ether-based molecular recognition from anhydrous organic solvents to aqueous media. It is helpful for achieving supramolecular polymerization driven by crown ether-based molecular recognition in a completely aqueous medium.

Synthesis and in vitro degradation of poly(alkylene carbonate anhydride)

A novel degradation posscably(alkylene carbonate anhydride) (PACA) was synthesized by the melt polycondensation reaction of the corresponding mixed inhydrides of the diearboxylic acid derived from oligoite-aramethylene carbonatediol (OTMCD) and oligothexamethylene carbonaterdiol (OHMCD). The polymers structure was confirmed by IR and H NMR spectroscopy DSC analysis showed PACA had a low T., (< -30°C). In vitro degradation tests indicated that the degradation rate of poly(alkylene carbonate) was more controiled with the incorporation of anhydride groups.