Full paperBionic design of cytochrome c oxidase-like single-atom nanozymes for oxygen reduction reaction in enzymatic biofuel cells
Graphical Abstract
Inspired by the native structure of enzymes, FeN5 SAs, with remarkably high cytochrome c oxidases-like activity (KM, 4.2 × 10−5 M) and competitive electrocatalytic performance towards ORR (E1/2, 0.61 V, neutral condition), were developed in this work. Coupling a glucose dehydrogenase bioanode, the FeN5 SAs-based glucose/O2 EBFC obtained a maximum power density of 149.2 ± 4.0 μW cm−2 with an open circuit potential of 0.40 ± 0.01 V.
Introduction
In biological system, oxygen reduction reaction (ORR) is an extremely important chemical transformation process [1]. Depending on the high oxidizing power of oxygen molecules, aerobic catabolism plays an integral role in living organisms by providing energy to sustain the vital activities of lifecycle [2]. To harness the thermodynamic potential of ORR, aerobic biology has evolved a variety of redox-active metalloenzymes to transfer, bind and/or catalyze oxygen molecules [3], [4], [5]. In vivo, heme-contained proteins carry out numerous pivotal functions in these oxygen-involved biological processes by modifying the identity of their axial ligand, such as histidine, cysteine and tyrosine, and/or local structure within the distal binding pocket [2], [6]. Among them, cytochrome c oxidases (CcO), the terminal oxidase of cell respiration, accept electrons from ferrous cytochrome c (Cyt c) and catalyze four-electrons reduction of oxygen to water, which not only completes the electron transport of mitochondrial respiratory chain, but also protects organisms from the damage of toxic peroxo/superoxo chemicals [5]. Synchronously, the protons pumping process is carried out on mitochondrial membrane to create a driving force for ATP synthesis and other energy-requiring biological reactions [7]. Similar to other natural enzymes, however, the biochemical researches of CcO are usually restricted by the intrinsic drawbacks of enzymatic proteins [8], [9], [10], [14], such as short active lifetime, ease of denaturation and low tolerance towards ambient environments. In response to these limitations, developing an nanozyme, with low cost, high stability and adjustable activity, to substitute CcO would be an alternative solution [11], [12], [13].
Recent studies showed that inorganic nanoparticles, such as Cu2O and CeVO4, exhibited CcO-like activity [12], [13]. Compared with these existing nanomaterials that mimic natural enzymes functionally [15], [16], [17], [18], [19], designing an artificial enzyme, form the perspective of bionics [20], [21], [22], may provide a more reasonable and dependable research project to investigate the complex enzyme-like catalysis mechanisms [23]. According to X-ray structure analysis, the metal co-factors of natural CcO are fundamentally composed of two heme proteins (heme a, heme a3) and two copper centers (CuA, CuB), in which the redox-active transition metal ions adopt diverse ligand environments [5]. Among them, the active center of heme a3 is axial histidine (H376)-coordinated heme that plays a role of oxygen-binding site to activate and reduce oxygen to water by cooperating with CuB (CuⅠ) [2], [5]. In our previous reports, the iron single-atom nanomaterials of pyrolytic Zn MOF-encapsulated iron phthalocyanine (FePc) have been proved to possess prominent oxidase-like activities [22]. Through the atomic structure analysis, the active center of FeN5 is axial N-coordinated heme-like structure, which closely resembles the spatial structure of heme a3. Therefore, based on this bionic design, the CcO-like FeN5 single-atom nanozymes (FeN5 SAs) were developed in this work. Through the simulation of mitochondrial electron transport process, FeN5 SAs exhibited remarkable CcO-like activity to complete the electrons transport from ferrous Cyt c to oxygen molecules (Scheme 1a). Meanwhile, compared with natural CcO (Km, 10−5~10−8 M) [5], [24], steady-state kinetic analysis revealed the comparable affinity of FeN5 SAs (Km, 4.2 × 10−5 M) towards Cyt c. Furthermore, except for cellular respiration and oxidative phosphorylation, ORR is also the cathodic reaction in sustainable fuel cells [14], [25], [26], [27]. With atomically dispersed metal active sites, FeN5 SAs showed competitive electrocatalytic performance towards ORR with a half-wave potential (E1/2) of 0.67 V (vs. RHE) at neutral condition, which outperformed than that of commercial Pt/C (E1/2, 0.61 V). Coupling a glucose dehydrogenase (GDH) bioanode, this FeN5 SAs-based glucose/O2 enzymatic biofuel cell (EBFC) obtained a maximum power density of 149.2 ± 4.0 μW cm−2 with an open circuit potential of 0.40 ± 0.01 V (Scheme 1b). In this study, inspired by the native structure of enzymes, FeN5 SAs, with remarkably high CcO-like activity and competitive electrocatalytic performance towards ORR, are developed, which not only boosts the cross-merging between single-atom nanomaterials and artificial enzymes, but also provides rational entry points to guide the bionic research of next-generation nanozymes.
Section snippets
Chemical materials
Iron (Ⅱ) phthalocyanine (92%) was purchased from Energy Chemical, Shanghai, China. 2,2′-Bipyridine-5,5′-dicarboxylic acid (98%) was purchased from Jilin Chinese Academy of Sciences - Yanshen Technology Co., Ltd. Lauric acid was purchased from Guangzhouxilong, China. Glucose dehydrogenase (GDH) (from Pseudomonas sp.) (200 U mg−1) and Polyvinylpyrrolidone (mol wt 40,000) were purchased from Sigma-Aldrich. Zinc acetate (99%) was purchased from Aladdin, Shanghai, China. Cytochrome C (from equine
Results and discussion
In this work, FeN5 SAs were synthesized by pyrolyzing the host-guest structure of Zn MOF-encapsulated FePc at 900 °C under N2 atmosphere. The fusiform morphology of FeN5 SAs, with an average length about 500 nm, and atomically dispersed iron atoms were clearly characterized by SEM (Fig. 1a) and HAADF-STEM (Fig. 1b), respectively, which was well consistent with our previous reports [22]. As is well known, in mitochondrial respiratory chain, Cyt c, as an important electron carrier, completes the
Conclusions
From the perspective of bionics, the CcO-like single-atom nanozymes of FeN5 SAs were developed in this study. Through the simulation of mitochondrial respiratory chain, the remarkably high CcO-like activity and comparable affinity (Km, 4.2 × 10−5 M) towards ferrous Cyt c indicate the potential application of FeN5 SAs in biochemical researches. Meanwhile, benefiting from the atomically dispersed metal active sites and heme a3-like bionic structure, FeN5 SAs display competitive ORR
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (no. 21675151, 21721003, and 22074137) and the Ministry of Science and Technology of China (no. 2016YFA0203203).
He Zhang received his B.S. in Chemistry from Shandong Normal University (2015), and Ph.D. from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (2020) under the supervision of Prof. Shaojun Dong. His current interests concentrate in enzymatic biofuel cells and bio-photoelectrochemical systems.
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2023, Chemical Engineering JournalCitation Excerpt :As an artificial enzyme which is expected to replace natural enzyme, nanozymes not only has the catalytic performance of simulating natural enzyme, but also has the inherent characteristics of nanomaterials. At present, the types of nanozymes that have been widely studied mainly include peroxidase [23,24], oxidase [25,26], catalase [27,28] and superoxide dismutase [29,30]. A large number of nanozymes (carbon based [31], metal organic frameworks (MOFs) [32], metal oxide [33], metal alloy [34], etc.) have been widely studied and show great application prospects [35].
He Zhang received his B.S. in Chemistry from Shandong Normal University (2015), and Ph.D. from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (2020) under the supervision of Prof. Shaojun Dong. His current interests concentrate in enzymatic biofuel cells and bio-photoelectrochemical systems.
Liang Huang received his B.S. in Chemistry from Nanjing University of Aeronautics and Astronautics (2014) and Ph. D. from Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (2019) under the supervision of Prof. Shaojun Dong. His current research interests concentrate in the atomic engineering of nanomaterials for electrocatalysis and heterogeneous catalysis.
Jinxing Chen received his B.S. in Chemistry from Changchun University of Technology in 2016. He is currently a Ph.D. candidate supervised by Prof. Shaojun Dong at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. His research direction is mainly focused on the design of biomimetic nanozymes for biosensing.
Ling Liu is an Associate Professor at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences (CAS). Since 2018, she has been working as an on-the-job doctoral candidate in the Northeast Institute of Geography and Agroecology, CAS. Her research interests concentrate in analytical and electroanalytical methods, mainly for environmental detection and risk assessment, especially for in-site and on-line monitoring. The instruments used for detecting biochemical oxygen demand, water total toxicity, coliform group, and so forth, have been commercialized. She has published 27 papers in peer-reviewed international journals with an h-index of 14.
Xinyang Zhu received his B.S. in material chemistry from Harbin Engineering University (2017). He is currently a Ph.D. candidate supervised by Prof. Shaojun Dong at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. His research direction is mainly focused on the atomic engineering of nanomaterials for electrocatalysis.
Weiwei Wu received her B.S. from Central South University (2017). She is currently a Ph.D. candidate supervised by Prof. Shaojun Dong at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. Her research direction is mainly focused on the synthesis of functional nanomaterials with enzyme-like activities and the applications of nanozymes.
Shaojun Dong is a Professor of Chemistry at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, and a Fellow of the Academy of Sciences for the Developing World (1999). Her research interests concentrate in analytic chemistry and electrochemistry with interdisciplinary fields, such as chemically modified electrodes, nanomaterials, nanotechnology, bioelectrochemistry, spectroelectrochemistry, biofuel cells and energy devices. She has published over 1000 papers in international refereed journals with 57,000 citations (h-index >115). She was selected as a global Highly Cited scientist in Chemistry (Clarivate Analytics) from 2014 to 2019.