Metal–organic frameworks (MOFs) are crystalline synthetic porous materials formed by binding organic linkers to metal nodes: they can be either rigid1,2 or flexible3. Zeolites and rigid MOFs have widespread applications in sorption, separation and catalysis that arise from their ability to control the arrangement and chemistry of guest molecules in their pores via the shape and functionality of their internal surface, defined by their chemistry and structure4,5. Their structures correspond to an energy landscape with a single, albeit highly functional, energy minimum. By contrast, proteins function by navigating between multiple metastable structures using bond rotations of the polypeptide6,7, where each structure lies in one of the minima of a conformational energy landscape and can be selected according to the chemistry of the molecules that interact with the protein. These structural changes are realized through the mechanisms of conformational selection (where a higher-energy minimum characteristic of the protein is stabilized by small-molecule binding) and induced fit (where a small molecule imposes a structure on the protein that is not a minimum in the absence of that molecule)8. Here we show that rotation about covalent bonds in a peptide linker can change a flexible MOF to afford nine distinct crystal structures, revealing a conformational energy landscape that is characterized by multiple structural minima. The uptake of small-molecule guests by the MOF can be chemically triggered by inducing peptide conformational change. This change transforms the material from a minimum on the landscape that is inactive for guest sorption to an active one. Chemical control of the conformation of a flexible organic linker offers a route to modifying the pore geometry and internal surface chemistry and thus the function of open-framework materials.
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The datasets supporting the findings of this study are available from the University of Liverpool, and can be found at http://datacat.liverpool.ac.uk/id/eprint/589.
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This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement number 692685) and from the Engineering and Physical Sciences Research Council (EPSRC; grant EP/J008834). We acknowledge the High Performance Computing (HPC) Materials Chemistry Consortium for providing access to UK’s national supercomputer ARCHER under EPSRC grant EP/L000202. We thank the Diamond Light Source for provision of beamtime on the I11 and I19 beamlines, and the X-ray crystallography facility of the School of Chemistry at the University of Manchester for the use of their Rigaku Oxford diffraction FR-X instrument to collect two of the single-crystal diffraction datasets.