Wilfred R. Hagen, Willy A. M. van den Berg, Walter M. A. M. van Dongen, Eduard J. Reijerse and Paul J. M. van Kan
The ground-state paramagnetism of synthetic cubane clusters, [Fe4S4L4]3-, can be of three types: pure spin, physical spin mixture, or spin-admixed. The former two types are also abundantly present in biology; a first biological example of the latter has recently been found in a ‘hybrid-cluster protein’. In this work the hybrid-cluster protein from Desulfovibriovulgaris, D. desulfuricans (wild type and Cys428Ser mutant), Escherichiacoli, and the Fe-hydrogenase from D. vulgaris have been studied to determine the EPR (with a main feature around g≈5) and ESEEM parameters, biological significance, and biological distribution of spin-admixed clusters.