Guest-Adaptable and Water-Stable Peptide-Based Porous Materials by Imidazolate Side Chain Control

The peptide-based porous 3D framework, ZnCar, has been synthesized from Zn2+ and the natural dipeptide carnosine (-alanyl-L-histidine). Unlike previous extended peptide networks, the imidazole side chain of the histidine residue is deprotonated to afford Zn-imidazolate chains, with bonding similar to the zeolitic imidazolate framework (ZIF) family of porous materials. ZnCar exhibits permanent microporosity with a surface area of 448m(2)g(-1), and its pores are 1D channels with 5 angstrom openings and a characteristic chiral shape. This compound is chemically stable in organic solvents and water. Single-crystal X-ray diffraction (XRD) showed that the ZnCar framework adapts to MeOH and H2O guests because of the torsional flexibility of the main His--Ala chain, while retaining the rigidity conferred by the Zn-imidazolate chains. The conformation adopted by carnosine is driven by the Hbonds formed both to other dipeptides and to the guests, permitting the observed structural transformations.