Lawrence Berkeley National Laboratory

X-ray magnetic circular dichroism (XMCD) measures the inner shell absorption difference between left and right circularly polarized (lcp / rcp) X-rays in the presence of a magnetic field, and provides a direct probe of the spin values localized in the specific metal site. In this study, Ni L-edge XMCD of Ni rubredoxin, and of H2 reduced Desulfovibrio desulfuricans, Desulfovibrio baculatus and Desulfovibrio gigas hydrogenases has been measured and analyzed. XMCD multiplets suggest a high spin NiII while XMCD effects also indicate non-zero Ni spin values for all these enzymatic Ni sites. XMCD sum rule analysis has been carried out to derive the semi-quantitative orbital and spin angular momentum for the Ni sites inside Ni rubredoxin and reduced D. desulfuricans hydrogenase.