Coordination Cages Selectively Transport Molecular Cargoes Across Liquid Membranes.

Bao-Nguyen T Nguyen,Tanya K Ronson,Duncan J Howe,Angela B Grommet,Hugh P Ryan,Jeanne L Bolliger,Jonathan R Nitschke,John D Thoburn

doi:10.1021/jacs.1c04799

Bao-Nguyen T Nguyen, Tanya K Ronson + Show 6 more

Open Access

https://doi.org/10.1021/jacs.1c04799

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Abstract

Chemical purifications are critical processes across many industries, requiring 10–15% of humanity’s global energy budget. Coordination cages are able to catch and release guest molecules based upon their size and shape, providing a new technological basis for achieving chemical separation. Here, we show that aqueous solutions of FeII4L6 and CoII4L4 cages can be used as liquid membranes. Selective transport of complex hydrocarbons across these membranes enabled the separation of target compounds from mixtures under ambient conditions. The kinetics of cage-mediated cargo transport are governed by guest binding affinity. Using sequential transport across two consecutive membranes, target compounds were isolated from a mixture in a size-selective fashion. The selectivities of both cages thus enabled a two-stage separation process to isolate a single compound from a mixture of physicochemically similar molecules.

Highlights

The binding properties of coordination cages1−9 in solution have been tailored to species ranging from gases10−22 to heavy metals,23 and neutral24−28 and charged29−34 compounds
Chemical separation using bulk liquid membranes43−45 has been seen as a promising prospect for many years
This process could be used as the basis for a continuous chemical compound filtering system, in which coordination cages constantly encapsulate and release target compounds from stock mixtures to the receiving phases

Summary

■ INTRODUCTION

The binding properties of coordination cages− in solution have been tailored to species ranging from gases− to heavy metals, and neutral− and charged− compounds. Such membranes consist of a fluid phase that is not miscible with two other liquids and separates them They have been demonstrated to separate ions and heavy metals− but not neutral molecules as yet. By selectively transporting neutral molecule guests across an aqueous layer, cages separate compounds from a mixture according to their binding affinity. Guest transport from the stock arm to the receiving arm is driven by the concentration gradient between the two sides of the membrane, which favors guest transport from the higher concentration stock arm to the lower concentration receiving arm in a continuous process This process could be used as the basis for a continuous chemical compound filtering system, in which coordination cages constantly encapsulate and release target compounds from stock mixtures to the receiving phases. Each host would continuously shuttle guest molecules, in contrast to a simpler biphasic batch extraction system where the extracted guest and host must first be separated before host reuse

■ RESULTS AND DISCUSSION

■ CONCLUSION

■ REFERENCES