Cytochrome electrochemistry

In the original paper, Eddowes and Hill (1977) had reported that, in addition to 4,4 bipyridine, 1,2 bis(4-pyridyl) ethylene (2) was a more effective promoter of cytochrome c electrochemistry than the 4,4 bipyridine and SSBipy was better than both. This lead Allen and colleagues (1984) to postulate that the prerequirement for successful promoter activity was bifunctionality of the form ... 

They found that they could assign the compounds tested to four main classes depending on the observed electrochemistry of cytochrome c (see Figure 3.89). 

At this point it was clear how SSBipy was adsorbed on the electrode and the timescale over which this occurred, as well as the role of the concentration of the initial solution. However, the actual mode of action of the adsorbed species still remained somewhat obscure. An important insight into this was provided by the work of Hill et al. in 1987 who studied the effect of partial substitution of the layer of adsorbed promoter on the electrochemistry of cytochrome c. 

K.D. Gleria, H.A.O. Hill, V.J. Lowe, and D.J. Page, Direct electrochemistry of horse-heart cytochrome c at amino acid-modified gold electrodes. J. Electroanal. Chem. 213, 333-338 (1986). 

J. Wang, M. Li, Z. Shi, N. Li, and Z. Gu, Direct electrochemistry of cytochrome c at a glassy carbon electrode modified with single-wall carbon nanotubes. Anal. Chem. 74, 1993-1997 (2002). 

G.C. Zhao, Z.Z. Yin, L. Zhang, and X.W. Wei, Direct electrochemistry of cytochrome c on a multi-walled carbon nanotube modified electrode and its electrocatalytic activity for the reduction of H2O2. Electrochem. Commun. 7, 256-260 (2005). 

The first reports on direct electrochemistry of a redox active protein were published in 1977 by Hill [49] and Kuwana [50], They independently reported that cytochrome c (cyt c) exhibited virtually reversible electrochemistry on gold and tin doped indium oxide (ITO) electrodes as revealed by cyclic voltammetry, respectively. Unlike using specific promoters to realize direct electrochemistry of protein in the earlier studies, recently a novel approach that only employed specific modifications of the electrode surface without promoters was developed. From then on, achieving reversible, direct electron transfer between redox proteins and electrodes without using any mediators and promoters had made great accomplishments. 

H. Allen, O. Hill, N.I. Hunt, and A.M. Bond, The transient nature of the diffusion controlled component of the electrochemistry of cytochrome c at bare gold electrodes an explanation based on a self-blocking mechanism. J. Electroanal. Chem. 436, 17-25 (1997). 

S.M. Chen and S.V. Chen, The bioelectrocatalytic properties of cytochrome c by direct electrochemistry on DNA film modified electrode. Electrochim. Acta 48, 513-529 (2003). 

J.M. Sevilla, T. Pineda, A.J. Roman, R. Madueno, and M. Blazquez, The direct electrochemistry of cytochrome c at a hanging mercury drop electrode modified with 6-mercaptopurine. J. Electroanal. Chem. 451, 89-93 (1998). 

F.A. Armstrong, A.M. Bond, H.A.O. Hill, B.N. Oliver, and I.S.M. Psalti, Electrochemistry of cytochrome c, plastocyanin, and ferredoxin at edge- and basal-plane graphite electrodes interpreted via a model based on electron transfer at electroactive sites of microscopic dimensions in size. J. Am. Chem. Soc. 111,91859189 (1989). 

O. Ikeda, M. Ohtani, T. Yamaguchi, and A. Komura, Direct electrochemistry of cytochrome c at a glassy carbon electrode covered with a microporous alumina membrane. Electrochim. Acta 43, 833—839 (1998). 

These arguments were apparently in contradiction with electrochemical results reported by Cruanes et al. (158), according to which the reduction of cytochrome c is accompanied by a volume collapse of 24 cm3 mol-1. This value is so large that it almost represents all of the reaction volume found for the investigated reactions discussed above. A reinvestigation of the electrochemistry of cytochrome c as a function of pressure, using cyclic and differential pulse voltammetric techniques (155), revealed a reaction volume of -14.0 0.5 cm3 mol-1 for the reaction... 

When using electrochemistry to monitor directly the Fe(III)/Fe(II) reduction it is important to keep in mind that cytochrome c, at pH 7, in the oxidised state has an overall charge of +7.5, whereas in the reduced state it has a charge of + 6.5. ... 

Recently, an inorganic promoter as [Ru(CN)5(Spy)]4 (Spy = 4-thio-pyridine) adsorbed on a gold electrode surface also proved to be very effective in the direct electrochemistry of cytochrome c the tetraanion not... 

The midpoint reduction potential of cytochrome c and the kinetics of its reduction by Fe(EDTA) are also significantly influenced by substitutions at Phe-82. As measured by direct electrochemistry at pH 6 to eliminate any... 

The first electrochemical studies of Mb were reported for the horse heart protein in 1942 (94) and subsequently for sperm whale Mb (e.g., 95) through use of potentiometric titrations employing a mediator to achieve efficient equilibriation of the protein with the electrode (96). More recently, spectroelectrochemical measurements have also been employed (97, 98). The alternative methods of direct electrochemistry (99-102) that are used widely for other heme proteins (e.g., cytochrome c, cytochrome bs) have not been as readily applied to the study of myoglobin because coupling the oxidation-reduction eqiulibrium of this protein to a modified working electrode surface has been more difficult to achieve. As a result, most published electrochemical studies of wild-type and variant myoglobins have involved measurements at eqiulibrium rather than dynamic techniques. 

The rich spectroscopy and electrochemistry of the heme moiety yields a wealth of opportunities for the denovo heme protein design to evaluate the success of the heme binding site design. Combinations of these spectroscopic and electrochemical methods are elucidating the structure and function of de novo heme proteins and illustrating that they serve as excellent bioinorganic model complexes for simple cytochromes. 

Bipyridine resembles nicotine in its pharmacological properties but is not as active. The 3,4 -bipyridine derivative 113 known as amrinone and its relatives are of interest as cardiotonic agents. 4,4 -Bipyridine has been tested as an insecticide, but it is not of practical value.It is used in the study of the electrochemistry of cytochrome c and acts as a polymerization catalyst or hardening agent for various resins. l-Hexyl-4,4 -bipyridinium salts are especially effective as electron carriers in photochemical hydrogen producing systems. l,l -Dimethyl-4,4 -bipyridinium (92 R = R = CHj) and l,l -dibenzyl-4,4 -bipyridinium... 

Electrochemistry of disulfide unit present in cytochrome c (cyt c) molecules on gold electrodes has also been reported [169]. Disulfide unit in cytochrome c is strongly adsorbed on Au electrodes and this slows down the electron-transfer rate to the heme group. More recently, Krylov et al. [170] have immobilized cytochrome c by self-assembling on the surface-modified Au electrodes. CV was applied to study how denaturation and renaturation of cytochrome c depend on the solution composition. 

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