Abstract
We provide a comprehensive approach to the formation and characterization of molecular monolayers
of the blue copper protein Pseudomonas aeruginosa azurin on Au(111) in aqueous ammonium acetate solution.
Main issues are adsorption patterns, reductive desorption, properties of the double layer, and long-range
electrochemical electron transfer between the electrode and the copper center. Voltammetry, electrochemical
impedance spectroscopy (EIS), in situ scanning tunneling microscopy (STM), and X-ray photoelectron
spectroscopy (XPS) have been employed to disclose features of these issues. Zn-substituted azurin, cystine,
and 1-butanethiol are investigated for comparison. Cyclic voltammetric and capacitance measurements show
qualitatiVely that azurin is adsorbed at submicromolar concentrations over a broad potential range. The
characteristics of reductive desorption suggest that azurin is adsorbed via its disulfide group to form a monolayer.
The adsorption of this protein on Au(111) via a gold-sulfur binding mode is further supported by XPS
measurements. In situ STM images with molecular resolution have been recorded and show a dense monolayer
organization of adsorbed azurin molecules. Direct electron transfer (ET) between the copper atom of adsorbed
azurin and the electrode has been revealed by differential pulse voltammetry. The rate constant is estimated
from electrochemical impedance spectroscopy and shows that ET is compatible with a long-range ET mode
such as that anticipated by theoretical frames. The results constitute the first case of an electrochemically
functional redox protein monolayer at single-crystal metal electrodes.
Original language | English |
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Journal | Journal of the American Chemical Society |
Volume | 122 |
Issue number | 17 |
Pages (from-to) | 4047-4055 |
ISSN | 0002-7863 |
DOIs | |
Publication status | Published - 2000 |