Reticular Synthesis of Highly Crystalline Three-Dimensional Mesoporous Covalent-Organic Frameworks for Lipase Inclusion.

Abstract

The synthesis and application of three-dimensional (3D) mesoporous covalent-organic frameworks (COFs) are still to be developed. Herein, two mesoporous 3D COFs with an stp topology were synthesized in a highly crystalline form with aniline as the modulator. The chemical composition of these COFs was confirmed by Fourier transform infrared (FT-IR) and 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopies. These 3D mesoporous COFs were highly crystalline and exhibited permanent porosity and good chemical stability in both aqueous and organic media. The space group and unit cell parameters of COF HFPTP-TAE were verified by powder X-ray diffraction (PXRD), small-angle X-ray scattering, and three-dimensional electron diffraction (3D ED). The appropriate pore size of the COF HFPTP-TAE facilitated the inclusion of enzyme lipase PS with a loading amount of 0.28 g g-1. The lipase⊂HFPTP-TAE (⊂ refers to "include in") composite exhibited high catalytic activity, good thermal stability, and a wide range of solvent tolerance. Specifically, it could catalyze the alcoholysis of aspirin methyl ester (AME) with high catalytic efficiency. Oriented one-dimensional (1D) channel mesopores in HFPTP-TAE accommodated lipase, meanwhile preventing them from aggregation, while windows on the wall of the 1D channel favored molecular diffusion; thus, this COF-enzyme design outperformed its amorphous isomer, two-dimensional (2D) mesoporous COF, 3D mesoporous COF with limited crystallinity, and mesoporous silica as an enzyme host.