Zn-Car is a peptide-based metal organic framework (MOF) made up of tetrahedral zinc and carnosine . Carnosine is a dipeptide of beta-alanine and L-histidine. The histidine side chain contains an which can also bind to the metal. In this MOF, the imidazole group is deprotonated, so each carnosine molecule can bind to 4 metal atoms. The flexibility of this MOF is driven by the formation of hydrogen bonds between the guest molecules and carnosine. see animation