Electrode mimetic

The metal-centered redox potential is the most important criterion for the complex to be the SOD mimetic, since the catalytic disproportionation of O2 requires redox reactions between complex and superoxide (Scheme 9) (18). The complex redox potential should fall between the redox potentials for the reduction and oxidation of O2, viz. —0.16 and +0.89 V vs. NHE (normal hydrogen electrode), respectively (Scheme 1) (2). 

The mimetic biosensor for ELD described in Section ni.B.4.b, incorporating polymerized Fe-protoporphyrin IX (75c) and Os(II) ions, can be used for determination of diacyl peroxides in organic solution. The electrode was tested for determination of BzOOBz extracted from a pharmaceutical geP. ... 

Figure 8.2 shows an electrochemical system - a model of a catalase-biomimetic sensor, consisting of the reference electrode (Ag/AlCl/Cl ) and biomimetic electrode. In this system, the electrochemical potential changed as a result of mimetic electrode interaction with... 

The additional experimental proof of the last statement is given by data in Figure 8.5. Curve (a) shows the change of pH and potential in the mimetic electrode-H202-Cl--AgCl-Ag system. Curve (b) shows the results of tests carried out for the mimic applied on the electrode surface. According to these data, the potential abruptly decreases in the system, whereas curve (a) indicates its increase. 

In all Figures electrochemical potentials possess clear maxima and minima. Such curve shapes conform to the shape for catalase and electrochemical reactions in the diffusion zone of the system. As mentioned above, molecular oxygen accumulated on the surface of the mimetic electrode during catalase reaction (8.1) diffuses through the adhesive and mimic layers to the electrode surface, where it is activated and interacts with H+. Anions OFT formed in this process may set the electrode surface free for the next portion of oxygen by diffusion only. Thus, the rate of electrochemical reaction (8.2) will be defined by the ratio of the rates of molecular oxygen diffusion to the electrode surface and reverse diffusion of OH- anions from the surface. 

Based on the analysis of the obtained experimental regularities of the electrochemical process, it may be fundamentally concluded that the process at electrode displays a selfoscillation mechanism. Obviously, self-oscillations happen due to internal diffusion of the surface components of the mimetic electrode, which is not affected by solution mixing intensity. Mixing causes a strong influence on the external diffusion and OH- anion drainage from the interface layer. 

Studies on ethanol trace detection in aqueous solutions were carried out in an electrochemical cell of peroxidase-mimetic sensor of the potentiometric type, consisting of a reference electrode (Ag/AgCl) and a biomimetic electrode. Redistilled water was used for the background solution. The biomimetic electrode was prepared by adhering hematin-containing meroxidase mimetic to aluminum foil with Pattex adhesive [7, 8],... 

Figure 8.12 The apparent mechanism of peroxidase-mimetic electrode operation in electrocatalytic mode.

To check these suggestions, the authors conducted an experiment with a peroxidase-mimetic sensor prepared on a new aluminum electrode under conditions corresponding to one of the minima in Figure 8.14. As shown by the plot of this experiment (point A in Figure 8.14), the minimum at C2H5OH concentration equal 10-3wt.% depends on aluminum foil conditions for a fresh electrode a sharp, jump-like increase of the potential is detected. 

Electrochemical impedance spectroscopy provides a sensitive means for characterizing the structure and electrical properties of the surface-bound membranes. The results from impedance analysis are consistent with a single biomembrane-mimetic structure being assembled on metal and semiconductor electrode surfaces. The structures formed by detergent dialysis may consist of a hydrophobic alkyl layer as one leaflet of a bilayer and the lipid deposited by dialysis as the other. Proteins surrounded by a bound lipid layer may simultaneously incorporate into pores in the alkylsilane layer by hydrophobic interactions during deposition of the lipid layer. This model is further supported by the composition of the surface-bound membranes and by Fourier transform infrared analyses (9). 

The membrane mimetic fructose dehydrogenase system for fructose sensing described in this paper is stable for at least several days. Activity loss appears to occur primarily due to desorption of Qa from the electrode surface since much electrode activity could be restored by exposure of the electrode to a solution containing an alternate lipophilic mediator, decylubiquinone. Efforts are underway to improve mediator retention with the hope that electrode stability can be increased further to a practical level. 

As explained in previous chapters (see Chaps. 1 and 2), an electrode of the first kind is one based on atoms or molecules and their corresponding cation or anion in solution. This type of electrode is most commonly used within the ionic liquids fields. Requirements for this class of reference electrode are that the atom or molecule used does not react with the ionic liquids. Additionally the corresponding cation or anion should be stable in the solvated form within the IL and should not have any corresponding undesirable chemical reactions with the IL components. If the reference electrode is based on a metal MImetal ion M" electrode system, and assuming the activity of the metal is 1 (which may not be true for specific cases), then the corresponding potential of the half-ceU is given by ... 

Lyon, J. L. and Stevenson, K. J. 2009. Peroxidase mimetic activity at tailored nanocarbon electrodes. ECS Trans. 16 1-12. 

In recent years, much attention has been focused on electrochemical studies of metalloporphyrins, not only as mimetic compounds of the iron porphyrin unit in heme proteins but also as potential electrocatalysts . Metalloporphyrins have been found to be applicable in both homogeneous and heterogeneous catalysis - and, because oxygen can be reduced directly through a 4-electron pathway on some transition metal porphyrins, catalysis in the heterogeneous electrochemical oxygen reduction reaction has received particular attention The application of metalloporphyrins to heterogeneous electrocatalysis requires their attachment to solid electrodes which can be realized based on chemisorption, chemical reactions with previously functionalized electrodes, chemical reactions with a functionalized polymer, incorporation of the porphyrin with the polymer film and electrochemical polymerization. 

Kmzatkowska K, Dolusic E, Dehaen W et al (2009) Gold electrode incorporating corrole as an ion-channel mimetic sensor for determination of dopamine. Anal Chem 81 7397-7405... 

---