Walking the seven lines: binuclear copper A in cytochrome c oxidase and nitrous oxide reductase.

The enzymes nitrous oxide reductase (N2OR) and cytochrome c oxidase (COX) are constituents of important biological processes. N2OR is the terminal reductase in a respiratory chain converting N2O to N2 in denitrifying bacteria; COX is the terminal oxidase of the aerobic respiratory chain of certain bacteria and eukaryotic organisms transforming O2 to H2O accompanied by proton pumping. Different spectroscopies including magnetic resonance techniques, were applied to show that N2OR has a mixed-valent Cys-bridged [Cu1.5+(CyS)2Cu1.5+] copper site, and that such a binuclear center, called CuA, does also exist in COX. A sequence motif shared between the CuA center of N2OR and the subunit II of COX raises the issue of a putative evolutionary relationship of the two enzymes. The suggestion of a binuclear CuA in COX, with one unpaired electron delocalized between two equivalent Cu nuclei, was difficult to accept originally, even though regarded as a clever solution to many experimental observations. This minireview in honor of Helmut Sigel traces several of the critical steps forward in understanding the nature of CuA in N2OR and COX, and discusses its unique electronic features to some extent including the contributions made by the development of methodology and the discovery of a novel multi-copper enzyme. Left: X-band (9.130 GHz) and C-band (4.530 GHz, 1st harmonic display of experimental spectrum) EPR spectra of bovine heart cytochrome c oxidase, recorded at 20K. Right: Ribbon presentation of the CuA domain in cytochrome c oxidase and nitrous oxide reductase.

Exposure to Metals Can Be Therapeutic.

Because of the widespread epigenetic changes ensuing from carcinogenesis, structural and chemical features of chromatin provide unique targets for developing safer and more effective anticancer drugs. Metal-based agents have a potential advantage over other small molecular species in that characteristics of coordination geometry, redox state and ligand exchange allow one to fine-tune reactivity and affinity properties in a distinct fashion. This intersection of chromatin biology and bioinorganic medicinal chemistry is the subject of multiple collaborations in and between Switzerland and Singapore.

Alfred Werner's role in the mid-20th century flourishing of American inorganic chemistry.

The development of organic and physical chemistry as specialist fields, during the middle and end of the 19th century respectively, left inorganic behind as a decidedly less highly regarded subfield of chemistry. Despite Alfred Werner's groundbreaking studies of coordination chemistry in the early 20th century, that inferior status remained in place - particularly in the US - until the 1950s, when the beginnings of a resurgence that eventually restored its parity with the other subfields can be clearly observed. This paper explores the extent to which Werner's heritage - both direct, in the form of academic descendants, and indirect - contributed to those advances.

Stereochemistry of coordination compounds. From alfred werner to the 21st century.

As a contribution to the scientific symposium, November 22nd, 2013, commemorating the Nobel Prize awarded to Alfred Werner in 1913, a presentation of the development of stereochemistry of coordination compounds during the past 120 years was given. Stereochemistry was fundamental to Werner's theory of coordination compounds. After Werner's death in 1919, stereochemistry in this field did not progress much further for almost 20 years, but then developed continuously. It was realized that stereochemical features of elements showing coordination numbers larger than four are responsible for an almost unlimited number of stereochemical possibilities, thus opening a molecular world of new structures. In the beginning of the 21st century, interest in the field rose again considerably, mainly due to the potential of stereoselective catalysis, and the self-assembly of supramolecular structures. An end of these developments is not in sight. Here an abbreviated version of the lecture is given. A PowerPoint(®) file, or a video of the presentation, can be downloaded.

Alfred Werner's chemistry of dinuclear complexes--a test case of Werner's intuition.

The re-investigation of four original tris-bridged dinuclear dicobalt complexes from the Werner collection of the University of Zurich by X-ray diffraction studies is described. The complex [Co2(NH3)6(µ-NH2) (µ-OH)(µ-O2)](NO3)3 was studied recently. As the most interesting feature it was found to contain a µ-superoxo bridge, recognized by Alfred Werner and his coworker as an asymmetric peroxo bridge. The newly established µ-mono- and diacetato structures from crystals of the Werner collection, [Co2(NH3)6(µ-OH)2(µ-O2CMe)](NO3)3·H2O and [Co2(NH3)6(µ-OH)(µ-O2CMe)2](NO3)3·H2O, were assigned by Alfred Werner and his co-workers as mono- or di-bridged systems with the water functioning as η(1)-aqua ligands and not, as revealed by the X-ray diffraction studies, as solvate molecules. Similarly the exact nature of the µ(N, O) nitrito bridge in the structure of the [Co2(NH3)6(µ-OH)2(µ-O2N)](NO3)3·H2O complex from the Werner collection was left open in Werner's and his coworker's description. Only the accuracy of the X-ray diffraction study could ascertain any earlier 'good guess'. The assignment of the bridges of bridged dinuclear structures at Werner's time are well conceived considering the lack of appropriate analytical tools. The structural assignments of Alfred Werner for the discussed dinuclear complexes are therefore considered to deviate only marginally from the real structures. They are testimonies of Alfred Werner's predictive abilities in coordination chemistry supported by his prepared mind, his great abilities of intuition and conceptual thinking.

The color of complexes and UV-vis spectroscopy as an analytical tool of Alfred Werner's group at the University of Zurich.

Two PhD theses (Alexander Gordienko, 1912; Johannes Angerstein, 1914) and a dissertation in partial fulfillment of a PhD thesis (H. S. French, Zurich, 1914) are reviewed that deal with hitherto unpublished UV-vis spectroscopy work of coordination compounds in the group of Alfred Werner. The method of measurement of UV-vis spectra at Alfred Werner's time is described in detail. Examples of spectra of complexes are given, which were partly interpreted in terms of structure (cis ↔ trans configuration, counting number of bands for structural relationships, and shift of general spectral features by consecutive replacement of ligands). A more complete interpretation of spectra was hampered at Alfred Werner's time by the lack of a light absorption theory and a correct theory of electron excitation, and the lack of a ligand field theory for coordination compounds. The experimentally difficult data acquisitions and the difficult spectral interpretations might have been reasons why this method did not experience a breakthrough in Alfred Werner's group to play a more prominent role as an important analytical method. Nevertheless the application of UV-vis spectroscopy on coordination compounds was unique and novel, and witnesses Alfred Werner's great aptitude and keenness to always try and go beyond conventional practice.