Published:30 Sep 2016
Molybdenum and Tungsten Enzymes: Spectroscopic and Theoretical Investigations, ed. R. Hille, C. Schulzke, M. L. Kirk, M. L. Kirk, R. Hille, and C. Schulzke, The Royal Society of Chemistry, 2016, pp. P007-P008.
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It is all too fitting that these volumes dealing with the bioinorganic chemistry of molybdenum and tungsten be dedicated to three outstanding chemists whose contributions to the field over many years continues to inform, illuminate and inspire: Richard H. Holm, C. David Garner and John H. Enemark.
Prof. Holm has over 500 research publications (cited over 35 000 times) covering a wide range of nickel, iron and molybdenum chemistry (among other transition metals). He is perhaps most widely recognized for studies, beginning in the 1970s, that describe the synthesis and characterization of iron-sulfur clusters. This work came to include modelling the M and P clusters of nitrogenase, which perhaps provided the motivation to investigate models of mononuclear molybdenum-containing enzymes. His molybdenum work achieved great success with the synthesis of MoO2 models for enzymes of the sulfite oxidase, and later the DMSO reductase family, and the characterization of their properties as oxygen atom transfer catalysts. A key contribution was his use of bulky ligands to the metal that prevented µ-oxo dimerization, which had long stymied work in the field. He is Higgins Professor of Chemistry at Harvard University, a member of the National Academy of Sciences and the recipient of many other awards.
Prof. Garner already had a strong track record in the synthesis of copper and molybdenum complexes when, beginning in the late 1970s, he became one of the first researchers to apply the then-new analytical method of X-ray absorption spectroscopy not only to models of molybdenum enzymes but also to the enzymes themselves. The discovery of thiolate-like sulfur, Mo=O and Mo=S ligands to the metal in the active sites of enzymes such as sulfite oxidase, xanthine oxidase and DMSO reductase was critical in establishing the molybdenum coordination environment in these enzymes and greatly focused efforts to synthesize accurate structural and functional mimics of the enzymes. With over 300 publications (having over 8000 citations), he is presently Professor Emeritus at the University of Nottingham and a Fellow of the Royal Society. He is also past President of the Royal Society of Chemistry.
Prof. Enemark was already well recognized for his work on metal nitrosyls and related systems when he began to exploit the tris-pyrazolylborate ligand as a scaffold on which to construct and study MoO2 and MoO complexes. This work led to the synthesis and characterization of the first model that fully mimicked the catalytic cycle of oxotransferase enzymes such as sulfite oxidase. Enemark also played an instrumental role in the work that led to the first crystal structure of sulfite oxidase. Since that time, Enemark has pioneered the application of pulsed EPR methods to molybdenum enzymes and synthetic models of their active sites; work that has led to a deep understanding of not simply the physical but also the electronic structures of these systems. With over 250 publications and 10 000 citations, he is Regents Professor of Chemistry at the University of Arizona, a former Fulbright Scholar and recipient of the Humboldt Research Prize, among other national and international recognitions.