Preface to Volume 20. Transition Metals and Sulfur: A Strong Relationship for Life

Transition metal-sulfur sites play key roles in biology. In general, many transition metal ions – also often called trace elements – are essential to all living organisms. Notably, the number of these essential elements increased over the years, and the list of their biological functions has also grown steadily. Remarkable progress has been made in understanding the chemistry operating at the biological sites, furthermore early on it became likely that many transition metal ions harbor sulfur ligands in the metal coordination sphere. The structure and the reactivity of these metal-sulfur centers was quite different from anything found in regular coordination complexes. Yet, biomimetic inorganic chemistry, modern spectroscopic techniques, and high resolution protein crystallography made important contributions to unravel the properties of the metal-sulfur sites, with iron-sulfur and blue copper proteins as prime examples. In this volume of Metal Ions in Life Sciences the focus will be on some of the most intriguing, in our view, biological transition metal-sulfur sites. These include the blue type 1 Cu and the purple mixed-valent CuA electron transfer sites, the tetranuclear CuZ catalytic center of nitrous oxide reductase, the heme-thiolate complex in cytochrome P450, the iron-sulfur proteins with bound inorganic and organic sulfur, the pterin dithiolene cofactor coordinated to Mo or W, the polynuclear metal clusters of nitrogenase, the coupled siroheme-[4Fe-4S] center of sulfite reductase, the NiFeS sites of hydrogenases and CO dehydrogenase, and the Zn-finger domains. We are fully aware of the excellent books and authoritative reviews on various aspects of the subject, however, it is our motivation to cover in one single volume source this exciting domain of bioinorganic chemistry. In Chapter 1 the reader is introduced to the general subject “What is so exciting about transition metal sulfur sites in biology”, including a backward glance