东南大学张袁健团队报道了抗坏血酸氧化酶类Fe–N–C纳米酶的铁浸出和氧还原选择性研究。相关研究成果发表在2023年5月5日出版的《德国应用化学》。

抗坏血酸盐（H₂A）是一种著名的抗氧化剂，可以保护细胞成分免受自由基损伤，同时它也作为一种抗氧化剂用于癌症治疗。然而，H2A氧化的这种“矛盾”机制尚不清楚。

该文中，研究人员报道了使用Fe-N-C纳米酶作为铁蛋白模拟物，在催化H2A氧化过程中的Fe浸出及其对氧还原反应（ORR）选择性的影响。由于异质性，Fe-N-C中的Fe-Nx位点主要通过铁氧中间体催化H2A氧化和4e ORR。尽管如此，边缘N-C位点通过2e ORR产生的微量O₂积累并攻击Fe-Nx位点，导致当H2A浓度增加到2mM时，不稳定的Fe离子线性泄漏高达420ppb。

因此，Fe-N-C上相当一部分（约40%）的N-C位点被激活，最终实现了新的2+2e ORR路径，以及Fenton型H2A氧化。因此，在Fe离子扩散到本体溶液中后，N-C位点的ORR停止产生H₂O₂，这是H2A促氧化作用的起源。

附：英文原文

Title: Insights into Iron Leaching from an Ascorbate-Oxidase-like Fe–N–C Nanozyme and Oxygen Reduction Selectivity

Author: Xuwen Cao, Caixia Zhu, Qing Hong, Xinghua Chen, Kaiyuan Wang, Yanfei Shen, Songqin Liu, Yuanjian Zhang

Issue&Volume: 2023-05-05

Abstract: Ascorbate (H2A) is a well-known antioxidant to protect cellular components from free radical damage, meanwhile it is also emerged as a pro-oxidant in cancer therapies. However, such “contradictory” mechanisms underlying H2A oxidation are not well understood. Herein, we report Fe leaching during catalytic H2A oxidation using an Fe-N-C nanozyme as a ferritin mimic and its influence on the selectivity of the oxygen reduction reaction (ORR). Owing to the heterogeneity, the Fe-Nx sites in Fe-N-C primarily catalyzed H2A oxidation and 4e ORR via an iron-oxo intermediate. Nonetheless, trace O2 produced by marginal N-C sites via 2e ORR accumulated and attacked Fe-Nx sites, leading to the linear leakage of unstable Fe ions up to 420 ppb when the H2A concentration increased to 2 mM. As a result, a substantial fraction (~40%) of the N-C sites on Fe-N-C was activated, and a new 2+2e ORR path was finally enabled, along with Fenton-type H2A oxidation. Consequently, after Fe ions diffused into the bulk solution, the ORR at the N-C sites stopped at H2O2 production, which was the origin of the pro-oxidant effect of H2A.

DOI: 10.1002/anie.202302463

Source: https://onlinelibrary.wiley.com/doi/10.1002/anie.202302463