Small Molecular Probes for the Electron Transfer Pathways of Metalloproteins.
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Electron transfer reactions play important roles in many biological processes such as respiration and photosynthesis.We are interested in understanding the factors that control long-range electron transfer in biological systems.Although the effect of backbone structure on the rate of electron transfer has been well studied and documented, the effect of changing the "connection" between the metal and the protein backbone has remained unexplored.For example, in blue copper proteins, the copper ion is ligated by nitrogen, oxygen, and sulfur donors.This gives rise to the question: which "connection" is the fastest? We propose to study this by preparing a series of gold films where a copper complex is attached to an electrode via an alkylthiol linker.We can then measure the rate of transfer between the electrode surface and the copper center.Any differences will be due to the coupling efficiency of the metal through the nitrogen, oxygen, or sulfur linkage. In making the copper complexes, the copper(II) method was unsuccessful.This is because copper(II) prefers a coordination number of six, creating bis[tris(pyrazolyl)borato]copper(II).We were able to synthesize our desired copper complexes, (Hydrotris(pyrazolyl)borato)(X)copper(I) (X= aniline,phenol,and thiophenol), by the copper(I) route.This procedure was carried out in a Schlenk line so that copper(I) would not oxidize to copper(II).