The ability to rapidly thread and self-assemble polymer chains in aqueous media has found significant utility in materials and biological applications. Polyrotaxanes formed by the inclusion of long polymer chains inside cyclodextrins have been used to construct supramolecular gels (called slide-rings) for insulated molecular wires, transfection of DNA, and molecular imaging. In the past, the Smith group has shown that the encapsulation of squaraine dyes inside a tetralactam macrocycle occurs readily in nonpolar organic solvents, such as chloroform. The present work will discuss the synthesis of thiophene-containing squaraine dyes substituted with long polyethylene glycol (PEG) chains, which allows for both organic and water solubility. Their encapsulation within tetralactam macrocycles has been studied in organic and aqueous environments, and while it was found that association is slow in organic solvents, association in water leads to a &gt;300,000-fold increase in association rate and a 1,000-fold increase in the binding constant. Furthermore, it was shown that the length of the chain has minimal impact on association rate. The threading of these polymer chains has important mechanistic and functional ramifications, including giving potential insight into how living systems are able to thread biopolymers through small pores, as well as for molecular imaging applications and the development of long-range molecular shuttles that are able to rapidly translocate in aqueous environments.

Rapid threading of a long polyethylene glycol chain through a macrocycle in water

249th National Meeting (2015)

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