"Carbon precursor pre-coordination" strategy breaks precision synthesis bottleneck in single-atom nanozymes

Background：

Carbon-based single-atom nanozymes (C-SANzymes), characterized by their M-N_x active sites, have attracted significant attention as highly promising enzyme mimics. A critical approach to enhancing the catalytic performance of these nanozymes lies in the precise regulation of the coordination environment around metal atoms. For instance, introducing alternative elements to substitute coordinating N atoms and construct asymmetric coordination centers has been shown to finely tune the adsorption-desorption processes of reaction intermediates, thereby reducing energy barriers and improving catalytic performance. However, current synthesis strategies for C-SANzymes predominantly rely on empirical and harsh methods such as high-temperature pyrolysis, inert gas treatment, and acidic/alkaline conditions, which bring in the risk of metal aggregation due to the Gibbs-Thomson effect. Thus, the development of a mild and cost-effective approach for synthesizing C-SANzymes while maintaining precise control over their coordination environments remains a significant challenge.

Research Progress：

Professor Yanyan Jiang’s team at Shandong University, building on their prior theoretical work, proposed a "carbon precursor pre-coordination" strategy to precisely control the coordination environments of metal atoms in C-SANzymes. The core of this strategy involves pre-establishing specific metal-ion coordination environments by carefully selecting appropriate carbon and metal sources before the reaction, thereby enabling atomic-level regulation of the final coordination structures.

Targeting the natural active sites of CuZn-SOD and Mn-SOD，specifically the Cu-N₄ and Mn-N₄ coordination structure, the team employed ethylenediaminetetraacetic acid (EDTA) and ethylenediamine (EDA) as carbon sources. The abundant amino groups in EDTA and EDA acted as electron donors, pre-anchoring Cu²⁺ and Mn²⁺ ions via Cu-N and Mn-N bonds prior to the reaction. Remarkably, using only a household microwave oven, they successfully synthesized CuMn-CDs, in which Cu and Mn atoms were coordinated in Cu-N₄ and Mn-N₄ configurations—structures that are identical to the active centers found in natural CuZn-SOD and Mn-SOD—validating the effectiveness of this strategy (Fig. 1).

The researchers found that CuMn-CDs exhibited broader-spectrum antioxidant activity compared to natural CuZn-SOD and Mn-SOD. These nanomaterials efficiently scavenge multiple reactive oxygen and nitrogen species (RONS), including DPPH, ABTS, ·O₂⁻, ·OH, and H₂O₂, even at low concentrations (<20 µg mL⁻¹). Notably, CuMn-CDs maintained their catalytic activity for up to 180 days at room temperature (Fig. 2). Theoretical calculations revealed that both Cu and Mn sites could scavenge ·OH without additional energy input. Moreover, Mn sites converted ·O₂⁻ to H₂O with a low energy barrier of 0.49 eV, while Cu sites efficiently decomposed H₂O₂ into O₂ with a barrier of 0.48 eV (Fig. 3).

In functional validation, CuMn-CDs were utilized as free-radical scavengers in cigarette filters. With only 10 mg of CuMn-CDs (costing only $0.014 g⁻¹), 85.3% of free radicals in cigarette smoke were eliminated. Furthermore, filters incorporating CuMn-CDs significantly alleviated lung tissue damage and reduced oxidative stress in smoking mouse models (Fig. 2). Finally, the successful synthesis of other bimetallic systems (e.g., Cu/Zn, Fe/Ni, Co/Ce) further highlighted the universality of the "carbon precursor pre-coordination" strategy in achieving precise single-atom coordination control.

Perspective:

This study introduces a pioneering "carbon precursor pre-coordination" strategy for the atomic-level regulation of single-atom coordination environments in C-SANzymes. By precisely mimicking the active sites of natural CuZn-SOD and Mn-SOD and using a household microwave oven for synthesis, the proposed method dramatically streamlines the production process of C-SANzymes. The resulting CuMn-CDs exhibited exceptional antioxidant capacity, effectively scavenging a wide range of RONS and show potential as effective additives in cigarette filters to mitigate smoking-induced lung damage. This work not only establishes a versatile platform for the rational design of C-SANzymes with customized active sites but also presents promising opportunities for applications in environmental remediation and biomedical fields.

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