Side-chain control of porosity closure in single- and multiple-peptide-based porous materials by cooperative folding

Porous materials are attractive for separation and catalysis—these applications rely on selective interactions between host materials and guests. In metal–organic frameworks (MOFs), these interactions can be controlled through a flexible structural response to the presence of guests. Here we report a MOF that consists of glycyl–serine dipeptides coordinated to metal centres, and has a structure that evolves from a solvated porous state to a desolvated non-porous state as a result of ordered cooperative, displacive and conformational changes of the peptide. This behaviour is driven by hydrogen bonding that involves the side-chain hydroxyl groups of the serine. A similar cooperative closure (reminiscent of the folding of proteins) is also displayed with multipeptide solid solutions. For these, the combination of different sequences of amino acids controls the framework's response to the presence of guests in a nonlinear way. This functional control can be compared to the effect of single-point mutations in proteins, in which exchange of single amino acids can radically alter structure and function. A family of dipeptide-based metal–organic frameworks has been shown to respond to the presence of guests in a cooperative manner controlled by one amino acid residue. When the linker features a serine residue, guest removal enables the formation of hydrogen bonds between the residue's side-chains, causing a conformational change that closes the MOF's porous domain.