Gold electrodes, modified, cytochrome

Figure 3.89 Cyclic voltammograms of 500 pm cytochrome c at a gold electrode modified by (a) 2-mercaptopyridine, (b> 2-mercaptosuccinic acid, 4,4 -dithiobis(butanoic acid), (d) 4-mercaploaniline. pH 7.0 phosphate buffer +0.1 M NaC104. Scan rale 50mVs . From Allen...

Y. Sato and F. Mizutani, Electrochemical responses of cytochrome c on gold electrodes modified with nucleic acid base derivatives - electrochemical and quartz crystal microbalance studies. Electrochim. Acta 45, 2869-2875 (2000). 

Within the promoter there can be subtle structural differences that influence the polar interaction with the protein. For example, Figure 5 illustrates the cyclic voltammograms of cytochrome c obtained at a gold electrode modified with isomers of pyridine-carboxylaldehyde-thiosemi-carbazone (PATS). 

Figure 5 Cyclic voltammograms of cytochrome c recorded at gold electrodes modified with different isomers of PATS...

Let us pass to other cytochromes. Cytochrome f (or cytochrome C552) (FW = 15 000), the crystal structure of which is known,11 is an electron carrier present in the photosynthetic chain and also possesses a positive overall charge. It exhibits a reversible Fe(III)/Fe(II) reduction at a gold electrode modified with 4,4/-dithiopyridine,12 Figure 10. 

Before leaving our discussion of cytochromes, it is instructive to examine the voltammetric response of cytochrome c at a gold electrode modified by hydroxoalkanethiol carbon chains of variable length, Figure 14.28... 

Cyclic voltammograms recorded in an aqueous solution of cytochrome c (pH 7.1) at gold electrodes modified by (a) 3-hydroxo-l-propanthiol (b) 11-hydroxo-l-undecanthiol. Scan rate 0.5 V s . T = 0°C... 

Fig. 1.1. (a) SPR angle shifts (A pi) showing the electrostatical adsorption of cytochrome-c on gold electrode surfaces modified with a 3-mercaptopropionic acid SAM (I) after addition of cytochrome-c to a final concentration of ca. 2.5 x 10 M in 5 mM Na-phosphate pH 7.0 (full fine) or in 5 mM Na-phosphate, 100 mM KCl pH 7.0 (dotted line) (11) after rinsing the surface with clean buffer solution, (b) Cyclic voltammograms of a monolayer of cytochrome-c adsorbed on a gold electrode modified with a 3-mercaptopropionic add SAM recorded in 5 mM Na-phosphate, pH 7.0, at 50, 100 and 200 mV s. Reproduced fix)m [214] with permission. 

DNA adsorbed on a glassy carbon electrode was also used as an effective electron promoter enabling electron transfer via hopping conduction through electrode/base pair/cytochrome c by Ikeda et al. [128]. Gold electrodes modified with short oligonucleotides inunohilized via thiol chemisorption were described hy Lisdat et al. [129] to study the promotion of electron transfer to cytochrome c. 

Oxidation and reduction of cytochrome c at a gold electrode, modified by treatment with 4,4 -bipy, is close to reversible but shows additional potential-independent processes before and after the electron transfer. Absorption of the protein on the electrode surface takes place to allow rapid electron transfer and it is suggested that the heme edge is oriented to the surface. 

Sato Y, Mizutani F (1997) Electrochemical responses of cytochrome c on a gold electrode modified with mixed monolayers of 3-mercaptopropionic acid and n-alkanethiol. 438 99-104... 

Modified electrodes for biocatalysis use either electron mediators or promoters immobilized on the electrode surface -. In both cases, redox enzyme molecules are in solution and in contact with the common electron mediators for redox enzymes such as cytochrome c and ferredoxin. An electron promoter is not a mediator since it does not take part in electron transfer in the potential region of interest. An electrode modified with promoter molecules has enables some redox enzymes to directly transfer electrons. It has been shown that 4,4 -bipyridyl, bis(4-pyridyl)sulfide, and bis 4-pyridyl)disulfide are excellent promoters of electron transfer of cytochrome c. Cytochrome c gives a reversible cyclic voltammogram at gold electrodes modified with these promoters. 

Figure 3.96 The effect of increasing time of exposure (as indicated) of a gold electrode once-modified with SSBipy to thiophenol on the cyclic voltammetry of horse heart cytochrome t (0.4mM). 20 mM sodium phosphate/0.1 M NaCI04 pH 7.0. Scan rate 20mVs l. From Hill...

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). 

L. Wang and E.K. Wang, Direct electron transfer between cytochrome c and a gold nanoparticles modified electrode. Electrochem. Commun. 6, 49—54 (2004). 

Z.Q. Feng, S. Imabayashi, T. Kakiuchi, and K. Niki, Electroreflectance spectroscopic study of the electron transfer rate of cytochrome c electrostatically immobilized on the w-carboxyl alkanethiol monolayer modified gold electrode. J. Electroanal. Chem. 394, 149-154 (1995). 

Figure 10 Cyclic voltammograms at a modified gold electrode (see text) of (a) cytochrome c (b) cytochrome f. Aqueous solution buffered at pH 7.3...

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. 

Direct electrical communication between enzyme aetive sites and electrodes may also be facilitated by the nanoscale morphology of the electrode. The modification of electrodes with metal nanoparticles allows the tailoring of surfaees with features that can penetrate close enough to the enzyme aetive site to make non-mediated electron transfer possible. Electrodes modified by unaggregated 12 nm diameter gold nanoparticles have been found to have the eorrect morphology to allow direct electron transfer between the cytochrome c active site and the eleetrode [41]. Elec-... 

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