XES determination of the electronic structure of the over-oxidized form of the Hydrogenophilus thermoluteolus hydrogenase

Here we propose to measure Ni K-beta X-ray emission spectroscopy and XAS to unambiguously assign the electronic structure to a recently reported oxygen-protected state of the hyperthermophile hydrogenase from Hydrogenophilus thermoluteolus (HtSH). Although the crystal structure of this state indicates an unusual coordination of the Ni with three bridging cysteine residues and a terminal bidentate glutamate, two possible electronic structures have been proposed, a closed-shell singlet with a Ni(IV) and a Fe(II) at the active site, and an antiferromagnetically coupled open-shell singlet with a Ni(III) and an oxidized Fe(III). The proposed spin selective XES measurements should provide definitive evidence to assign the correct electronic structure.