An approach to long-range electron transfer mechanisms in metalloproteins: In situ scanning tunneling microscopy with submolecular resolution
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Publication Details
Author list: Friis EP, Andersen JET, Kharkats YI, Kuznetsov AM, Nichols RJ, Zhang JD, Ulstrup J
Publisher: NATL ACAD SCIENCES
Place: WASHINGTON
Publication year: 1999
Journal acronym: P NATL ACAD SCI USA
Volume number: 96
Issue number: 4
Start page: 1379
End page: 1384
Number of pages: 6
ISSN: 0027-8424
Languages: English-Great Britain (EN-GB)
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Abstract
In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, reflected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2- to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.
Keywords
azurin, Spectroscopy
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