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Two functionally different sets of ruthenium complexes were systematically studied to evaluate their potential utilization in the study of electron transfer in metalloproteins. The first set, developed to be covalently linked to metalloproteins, wasMoreTwo functionally different sets of ruthenium complexes were systematically studied to evaluate their potential utilization in the study of electron transfer in metalloproteins. The first set, developed to be covalently linked to metalloproteins, was evaluated according to labeling efficiency, excited state lifetime, and electron transfer efficiency. In this study, Cb5 was used as a reaction partner for the ruthenium complexes due to its robust nature and ease of expression. Marked differences in labeling efficiency over the most commonly used ruthenium complex were not noted, however, significant increases in the excited state lifetime and electron transfer efficiency were noted for the complex: Ru(bpz)2(phen-mal)2+. This complex was found to have a lifetime approximately 100ns longer and 2.5 fold greater labeling efficiency than the most commonly used complex.-The second set of ruthenium complexes, developed to mimic the binding site of cytochrome c and interact electrostatically with their reaction partners, was evaluated according to excited state lifetimes and electron transfer efficiency. When compared to 4Ru2, the current standard for this study, no marked improvement was found. However, it was noted that increasing the distance between the two redox centers indeed decreases the rate of electron transfer as predicted by Marcus Theory.-A third series of complexes of the form Ru(bpy)x(TMA-phen) 3-x+2+(3-x), which utilizes a quaternary amine to increase the overall charge of the complex, was prepared and examined in detail to access the overall impact of the amine on the properties of the complex. Electrochemical studies illustrated that the amine has essentially no inductive or other electronic effect on the complex. Also, the solvation effects appear relatively constant for the series of increasing charge. Studies of the temperature dependence of the excited state decay of Ru(TMAphen)35+ when compared to Ru(mephen)32+ suggest that the amine has very little impact on the excited state, though the slightly longer lifetime of Ru(TMAphen)35+ may suggest that the vibrational coupling of the excited state to the solvent is poorer for Ru(TMAphen) 35+ than for Ru(mephen)32+.