During the FunCapSys project we developed new approaches to enable capsules to sequester guests from an immiscible phase for separations and purifications. We have demonstrated the first example of coordination cages shuttling and transporting molecular cargoes reversibly between immiscible liquid layers and the use of sequential phase transfer of different cage species to separate their respective cargoes. As a proof of concept, this idea constitutes a new approach to molecular separations and may enable the development of lower cost molecular separation methods enabling significant energy saving. We also demonstrated the transfer of a supramolecular cage with controlled directionality between three phases, based on a cage that responds reversibly in two distinct ways to different stimuli. These results will open up opportunities to use such circulatory guest transport as a new mode of chemical purification. Moreover we have programmed information into related phase transfer systems allowing different functional outcomes in response to the distinct stimuli of heat and light.
Our research efforts have also shed light on the underlying mechanism of formation of new metal-organic container molecules from the readily available subcomponents. We have utilized the host-properties of these systems for a variety of applications such as catalysis and selective sensing of analytes including fluorometric detection of biologically relevant guests in an aqueous environment. We have also developed strategies to rationally modify the binding ability of cages through new post-assembly modification reactions.
We developed a new method for synthesising water soluble metal-organic container molecules representing a significant step forward in the design of abiological architectures able to trap, transport or transform chemicals in water or physiological media. We hope that the control of the solubility properties and stability of these nanocontainers will allow others and us to build sophisticated systems for sensing low levels of biologically relevant molecules or environmental pollutants present in urine or the bloodstream in the context of clinical diagnosis. Likewise, our structures may be suitable as vehicles to transport dyes for diagnostic imaging, or to deliver drugs across macroscopic distances. Ultimately, we hope that such water-soluble architectures may serve as nanoreactors for the preparation of new molecules of interest, such as pharmaceuticals, or for the degradation of toxic pollutants such as residual medicines and pesticides that can be found in water streams.
We also developed new and useful triangular-prismatic host frameworks with a remarkable ability to selectively bind a collection of pharmaceutically relevant molecules or toxic organochlorine pesticides. Whereas the central binding sites of most previously described capsules are roughly spherical, those of the triangular prisms are prolate. This decreased symmetry promoted the binding of a collection of complex natural products—steroids, opiates, alkaloids, and other drugs bound within the prisms. The flexible nature of the structures induced complex binding interactions involving collections of guests, including cooperative binding events and guest aggregation around the cage, underscoring the utility of our system to generate diverse host–guest dynamics from simple building blocks. The general concept of designing heteroleptic structures with smaller cavities than those of their homoleptic derivatives may provide a new method for optimizing the formation of low-symmetry structures that recognize diverse and targeted sets of prolate guests, including many pharmaceuticals beyond those explored so far. Such structures may serve as the basis of new chemical sensing and purification systems, enabling new liquid extraction methods that select for specific molecules within biological feedstocks.
