Bioinorganic applications of X-ray multiplets - The impact of Theo Thole's work

Prior to the work of Thee Thole and his collaborators, the vast majority of biological X-ray spectroscopy involved either EXAFS or hard X-ray XANES spectroscopy. Thee Thole's ligand field multiplet theory revealed the rich information content of transition metal L-edges, and it helped prompt the first measurements on metalloproteins. His contributions to XMCD also prompted the first low-temperature/high-field experiments on paramagnetic centers in proteins, This paper describes some recent work in biological soft X-ray spectroscopy that was stimulated by Thole's findings, Representative Ni protein absorption spectra are shown, illustrating detection of Ni(I), NL(III), and high-and low-spin Ni(II) in Ni hydrogenase and CO dehydrogenase, New XMCD spectra for Cu in plastocyanin and Fe in a 2Fe ferredoxin are presented. The exciting prospects for soft X-ray absorption and XMCD of metalloproteins are summarized. (C) 1997 Elsevier Science B.V.