Electrochemistry of self-assembled monolayers of the blue copper protein Pseudomonas aeruginosa azurin on Au(111)

We report the self-assembly and electrochemical behaviour of the blue coppe r protein Pseudomonas aeruginosa azurin on Au(111) electrodes in aqueous ac etate buffer (pH = 4.6). The formation of monolayers of this protein is sub stantiated by electrochemical measurements. Capacitance results indicate qu alitatively that the protein is strongly adsorbed at sub-mu M concentration s in a broad potential range (about 700 mV). This is further supported by t he attenuation of a characteristic cyclic voltammetric peak of Au(111) in a cetate solution with increasing azurin concentration. Reductive desorption is clearly disclosed in NaOH solution (pH = 13), strongly suggesting that a zurin is adsorbed via its disulphide group. An anodic peak and a cathodic p eak associated with the copper centre of azurin are finally observed in the differential pulse voltammograms. These peaks are, interestingly, indicati ve of long-range electrochemical electron transfer such as paralleled by in tramolecular electron transfer between the disulphide anion radical and the copper atom in homogeneous solution, and anticipated by theoretical frames . Together with reported in situ scanning tunnelling microscopy (STM) resul ts they constitute the first case for electrochemistry of self-assembled mo nolayers of azurin, even redox proteins. This integrated investigation prov ides a new approach to both structure and function of adsorbed redox metall oproteins at the molecular level. (C) 1999 Elsevier Science S.A. All rights reserved.