Jens Enevold Thaulov Andersen

Bio: Jens Enevold Thaulov Andersen is an academic researcher from Botswana International University of Science and Technology. The author has contributed to research in topics: Scanning tunneling microscope & Azurin. The author has an hindex of 23, co-authored 114 publications receiving 2171 citations. Previous affiliations of Jens Enevold Thaulov Andersen include University of Copenhagen & Technical University of Denmark.

Molecular Monolayers and Interfacial Electron Transfer of Pseudomonas aeruginosa Azurin on Au(111)

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 m...

Ordered Assembly and Controlled Electron Transfer of the Blue Copper Protein Azurin at Gold (111) Single-Crystal Substrates

Abstract: We have shown that Pseudomonas aeruginosa azurin can be immobilized on alkanethiol monolayers self-assembled on Au(111). Immobilization is achieved through hydrophobic interactions between the hydrophobic area around the copper atom in azurin and methyl heads of alkanethiol to form submonolayers or monolayers. In this orientation mode azurin molecules on Au(111) are oriented with the redox center (copper atom) facing the electrode surface. This is opposite to the orientation of azurin on bare gold which is via a surface disulfide group such as recently reported. Scanning tunneling microscopy (STM) with molecular resolution reveals that both well-ordered alkanethiol and protein adlayers are present. Adsorbed azurin molecules exhibit high stability and retain electron transfer (ET) function. Long-range interfacial ET between azurin and Au(111) across variable-length alkanethiol bridges was systematically investigated by different electrochemical techniques. Distance-dependent ET can be controlled by adjusti...

Two-Dimensional Cysteine and Cystine Cluster Networks on Au(111) Disclosed by Voltammetry and in Situ Scanning Tunneling Microscopy

Abstract: Microscopic structures for molecular monolayers of L-cysteine and L-cystine assembled on Au(111) have been disclosed by employing electrochemistry and in situ scanning tunneling microscopy (STM). High-resolution STM images show that the adlayers of both cyteine and cystine exhibit highly-ordered networklike clusters with (3√3 × 6)R30° structure. By combining the surface coverage estimated from voltammetric data, each cluster is demonstrated to include six individual cysteine molecules or three cystine molecules. As a comparison, no cluster structure is observed for the 1-butanethiol adlayer prepared and examined under the same conditions as those for cysteine and cystine. This suggests that intermolecular and intramolecular hydrogen bonds among adsorbed cysteine or cystine molecules could be responsible for the origin of the cluster−network structures for the adlayers. Several models are proposed and used to explain the in situ STM observations in detail.

Electronic properties of functional biomolecules at metal/aqueous solution interfaces

Abstract: Monolayers of molecules, which retain their function in the adsorbed state on solid surfaces, are important in materials science, analytical detection, and other technology approaching the nanoscale. Molecular monolayers, including layers of functional biological macromolecules, offer new insight in electronic properties and stochastic single-molecule features and can be probed by new methods which approach the single-molecule level. One of these is in situ scanning tunneling microscopy (STM) in which single-molecule electronic properties directly in aqueous solution are probed. In situ STM combined with physical electrochemistry, single-crystal electrodes, and spectroscopic methods is now a new dimension in interfacial bioelectrochemistry. We overview first some approaches to spectroscopic single-molecule imaging, including fluorescence spectroscopy, chemical reaction dynamics, atomic force microscopy, and electrochemical single-electron transfer. We then focus on in situ STM. In addition to high structu...

An approach to long-range electron transfer mechanisms in metalloproteins: In situ scanning tunneling microscopy with submolecular resolution

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.