Mechanical Bond Approach to Introducing Self-Adaptive Active Sites in Covalent Organic Frameworks for Zinc-Catalyzed Organophosphorus Degradation

Abstract

Mechanically interlocked molecules (MIMs) with discrete molecular components linked through a mechanical bond in space can be harnessed for the operation of molecular switches and machines, which shows huge potential to imitate the dynamic response of natural enzymes. In this work, rotaxane compounds were adopted as building monomers for the synthesis of a crown-ether ring mechanically intercalated covalence organic framework (COF). This incorporation of MIMs into open architecture implemented large amplitude motions, whose wheel slid along the axle in response to external stimulation. After impregnation with Zn 2+ ions, the relative locations of two zinc active sites (crown-ether coordinated Zn(II) and bipyridine coordinated Zn(II)) are endowed with great flexibility to fit the conformational transformation of an organophosphorus agent during the hydrolytic process. Notably, the resulting self-adaptive binuclear zinc center in a crown-ether-threaded COF network is endowed with a record catalytic ability, with a rate over 85.5 μM min –1 for organophosphorus degradation. The strategy of synthesis for porous artificial enzymes through the introduction of mechanically bound crown ether will enable significant breakthroughs and new synthetic concepts for the development of advanced biomimetic catalysts.

Building a Porous Molecular Machine That Replicates Natural Enzymes

“…In this issue of ACS Central Science , Yuan, Zhu, and co-workers demonstrate, for the first time, a new strategy for an industrially applicable “mimic” for OPH capable of degrading OPs. 2 …”

“…The thermal stability of the artificial enzyme is a key parameter for its practical usage; most natural-microorganism enzymes lose their activity as the temperature increases. 2 Central to their design philosophy is replicating the active domain of OPH, which involves two zinc fragments within a 3.3–4.6 Å distance, corresponding to the transition-state barrier crossing and the product-release steps, as depicted in Figure 1 . 3 These next-generation artificial enzymes are affectionately called nanozymes.…”

“…The excellent properties of the crown-ether ring threaded COF solid, such as its high activity, substantial stability, and excellent recyclability, confirm its considerable potential as porous artificial enzymes in real industrial applications. 2 …”

“…This mechanism is in line with the authors design philosophy, where the interlocked crown-ether ring slides along the COF skeleton to simulate the behavior of natural hydrolase. 2 …”

“…While multiple biotechnological applications across industry such as bioremediation are reliant on OPH, natural enzymes are not sufficiently stable for practical use. In this issue of ACS Central Science , Yuan, Zhu, and co-workers demonstrate, for the first time, a new strategy for an industrially applicable “mimic” for OPH capable of degrading OPs …”