Carbon Direct Electrochemistry Of Heme-containing Proteins

20 century is an energy source century. With the growing exhaustion of the fossil fuels, many countries are paid a big attention to the development and the application of the new kinds of the energy sources. The fuel cell as a clean energy transformation system with the high efficiency of energy transformation has been one of the hot investigation projects.The biofuel cell is a kind of the fuel cell with the bioelectrocatalyst and the biofuel. Except the advantages of the general fuel cell, biofuel cell is possessed of the many advantages, such as the fuels with the encyclic source and low price, operation conditions at the room temperature, the good biocompatibility etc. Therefore, it is being paid the attention. However, at present, the development of the biofuel cell is in the preliminary step. There are many difficult problems to be solved. The main problem is that the bioelectrocatalyst should be firmly fixed on the electrode without denaturation.In this thesis, the fixation of the heme-containing proteins, such as cytochrome c (Cyt c), myoglobin (Mb) and hemoglobin (Hb) on the active carbon using the balance adsorption method was investigated. The electrochemical behavior of the heme-containing proteins supported on the active carbon as well as their electrocatalytic activity and the stability for the reduction of O₂ or H₂O₂ were studied. It could lay the firm foundation for developing the cathodic biocatalysts of the biofuel cell. The main results are as follows:1. The glassy carbon (GC) electrodes modified with the carbon-supported Cyt c, Mb and Hb were prepared using the balance adsorption method. A pair of redox peaks can be observed in the cyclic voltammogram of each carbon-supported heme-containing protein. The separation of the peak potentials is about 60mV. The currents of the anodic and cathodic peaks are almost the same. It indicated that all the electrochemical reactions of three carbon-supported heme-containingproteins are direct and quasi-reversible. The measurements of the cyclic voltammograms at the different scan rates showed that the anodic and cathodic peak currents are proportional to the scan rate. It indicated that all the electrochemical reactions are not controlled with the confusion and demonstrated that each carbon-supported heme-containing protein is adsorbed on the active carbon. It was found that after 20 continuous cycles, the peak current is still stable. After the GC electrode modified with each carbon supported heme-containing protein is immersed in the phosphate buffer solution at 0°C for 7 days, the redox peak currents are almost the same as that before the immersion. All the above results illustrated that carbon supported Cyt c, Mb and Hb can undergo a stable, non-diffusion controlled, quasi-reversible and direct electrochemical reactions. Their formal potentials (￡°) are similar. They are -36K -371 Si 369mV, respectively, for the carbon supported Cyt c, Mb and Hb.2. The reason for that the Nafion membrane fixed, carbon supported Cyt c, Mb and Hb can undergo the quasi-reversible electrochemical reactions may be attributed to that the oxygen-containing groups on the surface of the active carbon can prevent from the denaturation adsorption of Cyt c, Mb, Hb and sulphonic acid group-containing Nafion makes water easy to enter into the heme-containing protein, leading to that their electrochemical reactions are promoted.3. Although the standard redox potentials of Cyt c, Mb and Hb are different, ￡°' of the Nafion membrane fixed, carbon supported Cyt c, Mb and Hb are almost the same. In addition, it was reported in the literatures that ￡° ofa heme-containing protein fixed on the different matrixes are different. These results indicated that microenvironment could significantly affect the electrochemical behaviors of the heme-containing proteins.4. The Nafion membrane fixed, carbon supported Cyt c, Mb and Hb showed the good electrocatalytic activity for the reduction of O2 or H2O2, indicating that the carbon supported Cyt c, Mb and Hb can keep their bioactivities. Therefore, the carbon supported Cyt c, Mb and Hb can be used as the cathodic biocatalysts of the biofuelCell.5. The preparation of the Nation membrane fixed, carbon supported Cyt c, Mb and Hb using the balance adsorption method is simple. The Nafion membrane fixed, carbon supported Cyt c, Mb and Hb obtained showed the good electrocatalytic activity for the reduction of O2 or H2O2. Therefore, it is a good method for preparing the cathodic biocatalyst of the biofuel Cell.