| By studying the electrochemical behavior and electrocatalytic properties of redox proteins on electrodes with electrochemical methods, we could understand the electron transfer mechanism and biological function in vivo, which are significant for theory and practice to construct biosensors and bioreactors. In fact, most chemical reactions during the metabolism are catalyzed by active protein-enzymes, and the basal movement in human body is charge movement. Cytochrome c (cyt-c) is located on the inner mitochondrion membranes of living cell, and is a part of the electron transport chain. As its redox reaction in vivo may be considered as a model and test system for bioelectrochemical redox ones, its electrochemical properties have been studied extensively. In this work, protein film voltammetry (PFV) was reviewed detailedly, and then a series of research and exploration on direct electrochemistry of cyt-c were carried out by PFV. The details are as follows:Cyt-c was electrostatically adsorbed on the surface of the edge plane pyrolytic graphite electrode (EPPGE). Then, the relationship between redox potential of cyt-c and pH and the scan rate was studied by PFV, thus to investigate proton-coupled electron transfer of cyt-c directly adsorbed on EPPGE surface. Results suggested that the reduction of ferricytochrome c is independent of proton, but the oxidation of ferrocytochrome c is coupled by a slow one-proton transfer process.Because direct adsorption of cyt-c on the EPPGE surface is not firm, electrochemical signals of cyt-c would not be monitored any longer if the electrode was rinsed strongly or immersed in solution for more than five minutes. Therefore, cyt-c entrapped in sodium alginate (SA) and agarose hydrogel was electrostatically bound to EPPGE, thus to prepare stable hydrogel-cyt-c/EPPGE. Then, direct electrochemistry between cyt-c and the electrodes, effects of ionic strength, pH and exterior substances on the direct electrochemistry, and electrocatalytic properties of cyt-c were monitored by PFV. Results showed that the electrochemical behavior of Heme Fe(III)/Fe(II) in cyt-c is quasi-reversible, and the peak currents are inhibited by exterior metal ions. Catalytic reduction of oxygen could be achieved by the hydrogel-cyt-c/EPPGE, which means that it could be developed into a kind of biological sensor for dissolved oxygen possibly.Ionic liquids can be used as ideal mediums for some bio-catalytic processes, in which proteins are not inactivated but more stable than in other organic solvents. In this paper, direct electrochemistry of cyt-c entrapped in agarose hydrogel on gold electrode (Au), EPPGE and glassy carbon electrode (GC) in two room temperature ionic liquids was investigated. The effects of the addition of DMF in the agarose-cyt-c film, water concentration in ionic liquids and exterior metal ions on the electrochemical behavior of cyt-c were monitored, and electrocatalytic properties of cyt-c were also done. Results showed that a good quasi-reversible redox behavior of cyt-c could be found after adding DMF in agarose-cyt-c film, and peak shape would not change after continuously scanning for 50 cycles. In addition, a certain amount of water in hydrophilic ionic liquids is necessary to maintain electrochemical activities of cyt-c, electrochemical performance of cyt-c is the best when the water content is 5.2% and 5.8% for [Bmim][Br] and [Bmim][BF4] respectively. However, electrochemical activities of cyt-c are inhibited by exterior metal ions. Interestingly, Cyt-c entrapped in agarose hydrogel on EPPGE and GC could catalyze the electroreduction of trichloroacetic acid and t-BuOOH in [Bmim][BF4], but could not in [Bmim][Br]. Reasons for above-mentioned differences of electrochemical properties of cyt-c in different ionic liquids were preliminarily discussed. |
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