Measurement of Electron Transfer Rates between Adsorbed Azurin and a Gold Electrode Modified with a Hexanethiol Layer
✍ Scribed by Adolfas K. Gaigalas; Gediminas Niaura
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 210 KB
- Volume
- 193
- Category
- Article
- ISSN
- 0021-9797
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✦ Synopsis
In this work we report the application of electroreflectance (ER) tween the proteins involved in redox transformations and spectroscopy for the study of the redox reaction of the nonheme provide a pathway for the electron transfer (ET). It has been protein azurin. Azurin was irreversibly adsorbed on a polycrystalsuggested that the hydrophobic protein surface region near line gold surface modified with a hexanethiol layer. Surface-enthe Cu center in azurin plays an important role in the ET hanced resonant Raman spectroscopy (SERRS) demonstrated process and acts as a binding site (4, 5). Experiments perthat the immobilized azurin's copper site remained intact upon formed using site-directed mutagenesis supported the imporadsorption and that it underwent reversible reduction-oxidation.
tance of the hydrophobic patch in ET between its physiologi-Cyclic voltammetry (CV) data showed that the peak current of cal redox partners, cytochrome c 551 and nitrite reductase, as the oxidation (or reduction) wave depended linearly on the sweep rate as appropriate for an immobilized species. The formal poten-well as in the case of self-electron-exchange reaction (6, tial of the adsorbed azurin was 95 { 8 mV vs Ag/AgCl electrode, 7). The hydrophobic surface prepared by the adsorption of nearly identical to the earlier observed value of the native azurin alkanethiols on the gold electrode (8) may mimic the interin solution. All measurements were analyzed in the context of action site of the redox partners of azurin and provide a Marcus theory of electron transfer. The separation of the reducmodel system in which the ET process between an electrode tion-oxidation peaks in the CV data gave an estimate of the and the Cu site in the protein can be studied in detail. electron transfer (ET) rate in the range from 4 to 12 s 01 . ER, We have performed measurements on the azurin adsorbed with light of wavelength of 640 nm, yielded a strong signal at on hexanethiol modified gold electrode using surface-enthe same potential as the midpotential determined in CV. The hanced resonant Raman spectroscopy (SERRS), electrorefrequency dependence of the ER response was consistent with an flectance (ER), cyclic voltammetry (CV), and electrochem-ET rate of 150 to 200 s 01 . Electrochemical impedance measureical impedance (EI). The objective of the study was the ments indicated an ET rate of the order of 300 s 01 . The disparity between the ET rates measured with CV and ER suggests that characterization of the ET process, a topic of great impor-ET may not be a single-step process. The results also point to the tance both scientifically (9) and technologically (10). The importance of hydrophobic interactions in adsorption and redox structure of the active center was probed by the SERRS transformations of azurin. ᭧ 1997 Academic Press (11), while the dynamics of the ET process was studied by Key Words: adsorption; azurin; cyclic voltammetry; electron means of CV, ER, and EI. All of the measurements were transfer rate; electroreflectance; hexanethiol; SERRS.
analyzed using a unified kinetic model with the high temperature limit of Marcus ET rate expressions.