Copper proteins electrochemistry

The current chapter focuses on the electrochemistry of the ionic forms of copper in solution, starting with the potentials of various copper species. This includes the effect of coordination geometry, donor atoms, and solvent upon the electrochemical potentials of copper redox couples, specifically Cu(II/I). This is followed by a discussion of the various types of coupled chemical reactions that may contribute to the observed Cu(II/I) electrochemical behavior and the characteristics that may be used to distinguish the presence of each of these mechanisms. The chapter concludes with brief discussions of the electrochemical properties of copper proteins, unidentate and binuclear complexes. 

Redox catalysis is the catalysis of redox reactions and constitutes a broad area of chemistry embracing biochemistry (cytochromes, iron-sulfur proteins, copper proteins, flavodoxins and quinones), photochemical processes (energy conversion), electrochemistry (modified electrodes, organic synthesis) and chemical processes (Wacker-type reactions). It has been reviewed altogether relatively recently [2]. We will essentially review here the redox catalysis by electron reservoir complexes and give a few examples of the use of ferrocenium derivatives. 

Chi, Q.J., Zhang, J.D., Friis, E.P., Andersen, J.E.T., and Ulstrup,). (1999) Electrochemistry of self-assembled monolayers of the blue copper protein Pseudomonas aeruginosa azurin on Au(lll). Electrochemistry... 

The application of direct electrochemistry of small redox proteins is not restricted to cytochrome c. For example, the hydroxylation of aromatic compounds was possible by promoted electron transfer from p-cresol methylhydroxylase (a monooxygenase from Pseudomonas putida) to a modified gold electrode [87] via the blue copper protein azurin. All these results prove that well-oriented non-covalent binding of redox proteins on appropriate electrode surfaces increases the probability of fast electron transfer, a prerequisite for unmediated biosensors. Although direct electron-transfer reactions based on small redox proteins and modified electrode surfaces are not extensively used in amperometric biosensors, the understanding of possible electron-transfer mechanisms is important for systems with proteins bearing catalytic activity. 

Armstrong, F.A., Hill, H.A.O., Oliver, B.N. and Whitford, D. (1985) "Direct Electrochemistry of the Photosynthetic Blue Copper Protein, Plastocyanin. Electrostatic Promotion of Rapid Charge Transfer at an Edge-oriented Pyrolytic Graphite Electrode", J. Am. Chem. Soc., 107, 1473-6. 

Moreover, within the recent developments in Bioelectrochemistry, relevant attention has been devoted to the electrochemistry of redox proteins and redox enzymes (H.A.O. Hill), as welt as of synthetic models of copper proteins (J.O. Cabral). 

The direct electrochemistry of redox proteins such as ferredoxin and blue copper protein was studied. The additional effect of poly(L-lysine) on the redox behaviour of horse heart cyt c at functional electrodes has been reported Electropolymerized films such as PAn undergo redox reactions producing a colour change. This is described in Sect. 5.2. The anodic oxidation of poly(iV-vinylcarbazole) films was shown to involve initially the cross-linking of the polymer chains by oxidation of the carbazole moieties and dimerization of the resulting pendant carbazole cation radicals The resulting dimeric carbazole unit is more easily oxidized than the monomer and undergoes a further (reversible) two-electron oxidation. 

The TPQ reduction potential shows a linear variation with pH of -60 mV/pH, indicating a 2e. 211 ET process, in contrast to the 2e, 3H ET observed with model compounds." Presumably the protein matrix or nearby Cu(II) stabilizes the deprotonated topaquinol. No copper electrochemistry was observed. It is not clear whether the copper potential is anomalously low or if it could not be measured due to weak electronic coupling with the phenyl-alkynyl bridge. 

---