Shape sorting of two distinct amino acid residues at the multiple binding sites of a porous metal-macrocycle framework

Abstract

The arrangement of amino acids within crystalline porous materials represents a unique approach to enhance their functionalities such as catalysis, separation and sensing. In particular, the simultaneous arrangement of distinct residues in crystalline frameworks, i.e., shape sorting, remains one of the most important challenges. Here, we demonstrate the shape sorting of two distinct amino acid residues, tryptophan and serine, within porous metal-macrocycle framework-1 via precise molecular recognition at multiple binding sites on the pore surface. Single-crystal X-ray diffraction analysis showed that the indole ring of an N-protected tryptophan molecule was effectively encapsulated within a binding pocket located at the bottom corners of the nanochannel, forming multipoint hydrogen bonds and CH–π interactions. In addition to tryptophan, N-protected serine was adsorbed onto the ceiling sites via multipoint hydrogen bonds. Moreover, modifying their protecting groups allowed us to control the relative positions of the two residues in the nanochannel. We further tested the co-adsorption of both residues in selective separation experiments. The results suggest that designing porous crystals with multiple binding sites is an effective strategy for precise heteroleptic arrangement of amino acid residues, resulting in enhanced functionalization of porous materials.