[4Fe4S]2+ clusters exhibit ground-state paramagnetism.

Journal of the American Chemical Society

PubMedID: 21488637

Rupnik K, Lee CC, Hu Y, Ribbe MW, Hales BJ. [4Fe4S]2+ clusters exhibit ground-state paramagnetism. J Am Chem Soc. 2011;133(18):6871-3.
Two proteins involved in nitrogen fixation contain ferredoxin-type [4Fe4S] clusters that exist in paramagnetic ground state upon oxidation, a property never observed since the discovery of ferredoxins 50 years ago. This unique characteristic suggests a specific coupling in these clusters necessary for nitrogen fixation and implies an evolutionary connection between the clusters in the two proteins.