Interfacial electron transfer (ET) of biological macromolecules such as metalloproteins is the key process in bioelectrochemistry, enzymatic electrocatalysis, artificial ET chains, single-molecule electronic amplification and rectification, and other phenomena associated with the area of bioelectronics. A key challenge in molecular bioelectronics is to improve the efficiency of long-range charge transfer. The present work shows that this can be achieved by nanoparticle (NP) assisted assembly of cytochrome c (cyt c) on macroscopic single-crystalline electrode surfaces. We present the synthesis and characterization of water-soluble gold nanoparticles (AuNPs) with core diameter 3−4 nm and their application for the enhancement of long-range interfacial ET of a heme protein. Gold nanoparticles were electrostatically conjugated with cyt c to form nanoparticle−protein hybrid ET systems with well-defined stoichiometry. The systems were investigated in homogeneous solution and at liquid/solid interface. Conjugation of cyt c results in a small but consistent broadening of the nanoparticle plasmon band. This phenomenon can be explained in terms of long-range electronic interactions between the gold nanoparticle and the protein molecule. When the nanoparticle−protein conjugates are assembled on Au(111) surfaces, long-range interfacial ET across a physical distance of over 50 Å via the nanoparticle becomes feasible. Moreover, significant enhancement of the interfacial ET rate by more than an order of magnitude compared with that of cyt c in the absence of AuNPs is observed. AuNPs appear to serve as excellent ET relays, most likely by facilitating the electronic coupling between the protein redox center and the electrode surface.

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The oxidation behaviour of TP 347H FG in mixtures of water, oxygen, and hydrogen was investigated at 500, 600, and 700°C for a fixed oxidation time of 336 h. The samples were characterised using X-ray diffraction, reflective light and electron microscopy methods. Thin discontinuous double-layered oxide scales developed during oxidation at 500°C, whereas continuous double-layered oxide scales covered the entire sample surface after oxidation at 600 and 700°C. The major part of the inner oxide layer developed within the former alloy grains, whereas a Fe-Cr spinel formed along the former alloy grain boundaries. Transmission electron microscopy and electron energy loss spectroscopy investigations revealed that the part of the scale that grows into the alloy grains consists of particles of Fe-Cr spinel embedded in a metallic Fe-Ni matrix, which indicates that this part of the scale grows by an internal oxidation mechanism. The thickness of the inner oxide zone at high humidity (46%) is not significantly affected by the type of carrier gas used, whereas this thickness at low humidity (8% H 2 O) is sensitive for the carrier gas and increases in the following order: air \ Ar?7% H 2 \ Ar, indicating that the presence of oxygen or hydrogen in addition to a relatively low content of water vapour counteracts the effect of water vapour on the development of the inner oxide zone.

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