NIR-accelerated cascade reaction for degradation of organophosphorus compounds by Au/PTE/ZIF-8: cooperative effect and mechanism

An enzyme–gold nanoreactor for chemoenzymatic cascade degradation of methyl-paraoxon. Herein, we designed a NIR (near-infrared)-responsive multifunctional nanoreactor that can be used for precise and immediate regulation of chemoenzymatic degradation of organophosphates (OPs). The thermophilic phosphotriesterases (PTEs) and gold nanoparticles (AuNPs) were encapsulated in the ZIF-8 structure yielding an Au/PTE/ZIF-8 nanocomposite, which can be modulated by NIR as a result of the photothermal effect of AuNPs. The Au/PTE/ZIF-8 nanoreactor demonstrated excellent performance in mediating cascade reactions from enzymatic hydrolysis of OPs (>90% conversion in 10 min) to the subsequent reduction of the resulting 4-nitrophenol (4-NP) into 4-aminophenol (4-AP) by NaBH 4 (>90% yield of 4-AP in 30 min). An immediate light-to-heat conversion when NIR was applied to Au/PTE/ZIF-8 at room temperature enables a 2-fold increase in the specific activity of phosphotriesterase from S. islandicus compared to thermo-heating at 70 °C. Based on the fact that there was a significant acceleration in 4-NP reduction by Au/PTE/ZIF-8, we proposed a plausible reaction mechanism (reaction pathway) suggesting that: 1) cooperative actions between Au, ZIF-8 and substrates take place by promoting polarization and cleavage of the B–H bond in NaBH 4 for releasing hydride facilitating electron and hydride transfer to 4-NP; and 2) stabilizing the formation of intermediates or the transition state by coordination with a ZIF-8 delocalized network and/or Au.