Laccase, as a multi-copper oxidase, has attracted much attention in biofuel cell and bio-electrochemical sensor research because of its ability to achieve electrochemical reduction of oxygen molecules at lower overpotentials. Similar to other biological enzymes, laccases have a complex molecular structure. Copper ions in their active centers (T1 copper ions of oxidized phenolic substrates and T2-T3 copper clusters of reduced oxygen, Fig. 1) are buried deep inside the enzyme molecules. . These characteristics determine that it is difficult to achieve direct electron transfer of laccase molecules and bioelectrochemical catalysis based on this in conventional electrochemical systems, although these studies have extremely important significance in the basic and applied research of bioelectrochemistry.
Institute of Chemistry, Chinese Academy of Sciences, Institute of Chemistry, Living and Analytical Chemistry Mao Lanqun's team has been working on the electrochemistry of laccases and research on biofuel cells based on this earlier. They first discovered that laccase can achieve direct electron transfer between the electrode and the carbon nanotube electrode (Electroanalysis 2006, 18, 587-594). Further, they used this property to successfully develop a biofuel cell based on laccase direct electrocatalysis (Adv. Mater. 2006, 18, 2639; Electrochem. Commun. 2007, 9, 989; Electrochem. Commun. 2008, 10, 851; Fuel Cells 2009, 1, 85).
Recently, with the support of the National Natural Science Foundation of China, the Ministry of Science and Technology, the Chinese Academy of Sciences, and the China Postdoctoral Fund, they have made new progress in direct electrocatalytic oxygen reduction studies of laccases. Under normal conditions, the orientation of laccase on the surface of carbon nanotubes is random and disordered, and only a small amount of laccase molecules can achieve direct electron transfer between the electrodes. It was found that, in the preparation of laccase-carbon nanotube composites, the addition of 20% ethanol solution can significantly increase the electrochemically catalyzed current of the prepared electrode for oxygen. Combined with protein structure analysis, they revealed the mechanism by which ethanol regulates the catalytic performance of laccase-CNT complexes, ie, ethanol can act as a bridge small molecule, adsorbing on the surface of carbon nanotubes on the one hand, and improving its infiltration; on the other hand, Hydrogen bonds between ethanol molecules and phenolic substrate binding sites close to T1 copper ions in laccase (about 1 nm in diameter) promote the docking of carbon nanotube surfaces with laccase recesses, by optimizing the protein in the carbon The orientation on the nanotubes, in turn, promotes efficient direct electron transfer between the active sites of copper ions and the electrodes (Figure 2). Further, they found that the regulation of organic solvents is closely related to their polarity, enzymatic capacity and vapor pressure. Among them, acetone and acetonitrile, which also have lower polarity, weaker enzymatic capacity, and higher vapor pressure, can increase the electrochemical catalytic current of the electrode for oxygen. In contrast, dimethylformamide and dimethyl sulfoxide, which have higher polarity, strong enzymatic capacity, and low vapor pressure, cause the electrode to lose almost all its activity for the electrochemical reduction of oxygen. Compared to the reported method for improving the electrocatalytic activity of laccases, the use of organic solvent molecules to improve the direct electrocatalytic performance of laccase is more simple and effective. This research not only has important significance in the basic research of bioelectrochemistry, but also lays the foundation for the further construction of self-driven living body analysis and sensing based on the principle of biofuel cells. Related results were published in J. Am. Chem. Soc. 2017, 139, 1565-1574.
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