Exploring the fascination of metal-sulfur bonds, vivid colors, and electron transfer through proteins: A tribute to Harry B. Gray

The study of transition metals and their role in living matter has a long and distinguished history. This field, today referred to as Bioinorganic Chemistry, has evolved into a vibrant area of research. Progress is fueled by four main factors: (1) the use of high-tech spectroscopy to explore the structural and dynamic properties of molecules, (2) the molecular engineering and design of artificial enzymes, (3) the rapid determination of high-resolution structures of proteins and large protein complexes, and (4) the significant advancements in computational chemistry. First, I will take the reader on a brief journey "Meeting Harry B. Gray". Hereafter, significant basic work in the laboratory and crucial key findings will be presented that have enhanced our understanding of the structural and functional features of notable metalloenzymes with unique catalytic sites: (i) the blue type-1 Cu center and the trinuclear O₂ activating Cu cluster in ascorbate oxidase, (ii) the purple mixed-valent [Cu^1.5+(CyS^-)₂Cu^1.5+] copperA electron transfer center in nitrous oxide reductase and cytochrome c oxidase, (iii) intraprotein control of electron transfer rates by allosteric interactions within the green nitrite reductase cytochrome cd₁, and (iv) active site structure and reaction mechanism of the red pentaheme cytochrome c nitrite reductase based on crystallographic identification of reaction intermediates and density functional calculations. This topic is particularly apt for honoring Harry B. Gray, who has made numerous seminal contributions to modern Inorganic Chemistry, especially as we celebrate his 90th birthday.