Covalent Organic Framework Cladding on Peptide-Amphiphile-Based Biomimetic Catalysts.

Peptide-based biomimetic catalysts are promising materials for efficient catalytic activity in various biochemical transformations. However, their lack of operational stability and fragile nature in non-aqueous media limit their practical applications. In this study, we have developed a cladding technique to stabilize biomimetic catalysts within porous covalent organic framework (COF) scaffolds. This methodology allows for the homogeneous distribution of peptide nanotubes inside the COF (TpAzo and TpDPP) backbone, creating strong noncovalent interactions that prevent leaching. We synthesized two different peptide-amphiphiles, CFFVK and CFFVR, with lysine (K) and arginine (R) at the C-termini, respectively, which formed nanotubular morphologies. The CFFVK peptide-amphiphile nanotubes exhibit enzyme-like behavior and efficiently catalyze C-C bond cleavage in a buffer medium (pH 7.5). We produced nanotubular structures of TpAzo-CFFVK and TpDPP-CFFVK through COF cladding by using interfacial crystallization (IC). The peptide nanotubes encased in the COF catalyze C-C bond cleavage in a buffer medium as well as in different organic solvents (such as acetonitrile, acetone, and dichloromethane). The TpAzo-CFFVK catalyst, being heterogeneous, is easily recoverable, enabling the reaction to be performed for multiple cycles. Additionally, the synthesis of TpAzo-CFFVK thin films facilitates catalysis in flow. As control, we synthesized another peptide-amphiphile, CFFVR, which also forms tubular assemblies. By depositing TpAzo COF crystallites on CFFVR nanotubes through IC, we produced TpAzo-CFFVR nanotubular structures that expectedly did not show catalysis, suggesting the critical role of the lysines in the TpAzo-CFFVK.