Conformational control of the structure and properties of synthetic porous materials

This is a long-range basic research project that targets the synthesis of crystalline porous materials that respond to their chemical environment in the way that biological molecules do. Although the potential analogy between synthetic porous materials and biological molecules has been suggested for many years, we can now address this problem meaningfully for the first time because of the results on which the project is based. This will create immediate opportunities in fundamental science and understanding.

Porous materials underpin the separation and catalysis processes of the modern chemical industry by controlling the organisation of guests in their pores. These high-performing materials, such as zeolites and carbons, all have rigid structures that do not change regardless of their chemical environment: dynamics within this single structural minimum can be important, but the size and shape of the pores that control guest response are unchanged. In contrast, the biological molecules involved in sorting, separation and catalysis can respond in a flexible manner to their chemical environment. To do this, they use rotation about single bonds to restructure in the presence of guest molecules, adopting different structures within their conformational energy landscape. The responses are characterised as conformational selection and induced fit according to the nature of the final structure and its relationship to the accessible structural states of the biological molecule. This produces exquisite chemical selectivity by organising the diverse array of spatially ordered chemical functionality that is also characteristic of biological molecules for functional performance.

In contrast, we have not previously been able to prepare synthetic porous materials with controllably interconvertible structures accessible via single bond rotation, nor to introduce spatially ordered multiple chemical functions into a synthetic porous material that could restructure by such single bond rotation. The creation of tuneable synthetic porous materials that can controllably respond to guests as biomolecules do would offer pathways for the separation and transformation of small molecules that are distinct from those accessible to current synthetic porous materials.

In a recent paper in Nature, we reported a crystalline porous material that responds to guests like a biological molecule. Specifically, it displays both conformational selection and induced fit responses that demonstrate a conformational energy landscape created by different rotations of single bonds in the porous material structure: these responses are then used to controllably trigger guest uptake. This project will establish how to achieve and control such guest response by creating new families of such porous materials with diverse structure and chemistry. It will thus create a new direction in porous materials research.

This will be achieved by defining the synthetic chemistry required to introduce diverse chemical functionality that can broadly direct guest response, by ordering multiple functionalities precisely in space and by expanding the size and geometry of the pore systems. The resulting materials will offer new modes of guest response that will be understood through detailed evaluation of the arising structures and associated sorption behaviour. This will allow the design of improved materials based on knowledge of how to determine guest response through single bond rotation by chemistry and sequence. The range of new materials families with distinct conformational energy landscapes spanning pore sizes, geometries and chemical functionalities offer control of function in sorption, separation and catalysis by previously inaccessible mechanisms. This will allow us to evaluate and understand the impact of biomolecule-like conformational response on the capabilities of synthetic porous materials.