Guest-adaptable and water-stable peptide-based porous materials by imidazolate side chain control

Abstract

The peptide-based porous 3D framework, ZnCar, has been synthesized from Zn2+ and the natural dipeptide carnosine (β-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 448 m2 g-1, and its pores are 1D channels with 5 Å 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-β-Ala chain, while retaining the rigidity conferred by the Zn-imidazolate chains. The conformation adopted by carnosine is driven by the H bonds formed both to other dipeptides and to the guests, permitting the observed structural transformations. A peptide-based porous framework (ZnCar×DMF), which is formed by the assembly of Zn with carnosine, exhibits permanent microporosity and has pores of chiral shape. Zn-imidazolate bonding to the histidine side chain affords the chemical stability of the framework in water, and the His-β-Ala main chain provides flexibility while conferring structural adaptability on the framework in the presence of different guest molecules. © 2014 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.