Explore the vast range of titles available.

Complex IV in the respiratory chain of mitochondria and bacteria catalyzes reduction of molecular oxygen to water, and conserves much of the liberated free energy as an electrochemical proton gradient, which is used for the synthesis of ATP. Photochemical electron injection experiments have shown that reduction of the ferric/cupric state of the enzyme’s binuclear heme a ₃/Cu B center is coupled to proton pumping across the membrane, but only if oxidation of the reduced enzyme by O ₂ immediately precedes electron injection. In contrast, reduction of the binuclear center in the “as-isolated” ferric/cupric enzyme is sluggish and without linkage to proton translocation. During turnover, the binuclear center apparently shuttles via a metastable but activated ferric/cupric state (O H), which may decay into a more stable catalytically incompetent form (O) in the absence of electron donors. The structural basis for the difference between these two states has remained elusive, and is addressed here using computational methodology. The results support the notion that Cu B[II] is either three-coordinated in the O H state or shares an OH ⁻ ligand with heme a ₃ in a strained μ-hydroxo structure. Relaxation to state O is initiated by hydration of the binuclear site. The redox potential of Cu B is expected, and found by density functional theory calculations, to be substantially higher in the O H state than in state O. Our calculations also suggest that the neutral radical form of the cross-linked tyrosine in the binuclear site may be more significant in the catalytic cycle than suspected so far.

A simple donor-acceptor linked dyad, 9-mesityl-10-methylacridinium ion (Acr ⁺-Mes) was incorporated into nanosized mesoporous silica-alumina to form a composite, which in acetonitrile is highly dispersed. In this medium, upon visible light irradiation, the formation of an extremely long-lived electron-transfer state (Acr •-Mes •⁺) was confirmed by EPR and laser flash photolysis spectroscopic methods. The composite of Acr ⁺-Mes-incorporated mesoporous silica-alumina with an added copper complex [(tmpa)Cu ᴵᴵ][Formula] (tmpa = tris(2-pyridylmethyl)amine) acts as an efficient and robust photocatalyst for the selective oxygenation of p -xylene by molecular oxygen to produce p -tolualdehyde and hydrogen peroxide. Thus, incorporation of Acr ⁺-Mes into nanosized mesoporous silica-alumina combined with an O ₂-reduction catalyst ([(tmpa)Cu ᴵᴵ] ²⁺) provides a promising method in the development of efficient and robust organic photocatalysts for substrate oxygenation by dioxygen, the ultimate environmentally benign oxidant.

\"This newest volume in the Wiley Series on Reactive Intermediates in Chemistry and Biology deals with the subject of oxidative processes mediated by copper ions within biological systems. The book addresses the significantly increasing literature on oxygen-atom insertion and carbon-carbon bond forming reactions as well as enantioselective oxidation chemistries. It covers a wide array of reaction types such as insertion and dehydrogenation reactions that utilize the cheap, abundant, and energy-containing the O2 molecule and progresses from biological systems to spectroscopy and related theory to bioinorganic models and applications\"-- \"This book is divided into three logical areas within the topic of Copper/Oxygen Chemistry: Biological Systems, Spectroscopy and Theory, and Bioinorganic Models and Applications\"--

Metalloenzymes effect a variety of important chemical transformations, often involving small molecule substrates or products such as molecular oxygen, hydrogen, nitrogen, and water. A diverse array of ions or metal clusters is observed at the active-site cores, but living systems use basic recurring structures that have been modified or tuned for specific purposes. Inorganic chemists are actively involved in the elucidation of the structure, spectroscopy, and mechanism of action of these biological catalysts, in part through a synthetic modeling approach involving biomimetic studies.

An efficient and selective four-electron plus four-proton (4 e - /4H + ) reduction of O 2 to water by decamethylferrocene and trifluoroacetic acid can be catalyzed by a synthetic analog of the heme a 3 /Cu B site in cytochrome c oxidase ( 6 LFeCu) or its Cu-free version ( 6 LFe) in acetone. A detailed mechanistic-kinetic study on the homogeneous catalytic system reveals spectroscopically detectable intermediates and that the rate-determining step changes from the O 2 -binding process at 25 °C room temperature (RT) to the O-O bond cleavage of a newly observed Fe III -OOH species at lower temperature (-60 °C). At RT, the rate of O 2 -binding to 6 LFeCu is significantly faster than that for 6 LFe, whereas the rates of the O-O bond cleavage of the Fe III -OOH species observed (-60 °C) with either the 6 LFeCu or 6 LFe catalyst are nearly the same. Thus, the role of the Cu ion is to assist the heme and lead to faster O 2 -binding at RT. However, the proximate Cu ion has no effect on the O-O bond cleavage of the Fe III -OOH species at low temperature.

The objectives of this and the following paper are to identify commonalities and disparities of the extended environment of mononuclear metal sites centering on Cu, Fe, Mn, and Zn. The extended environment of a metal site within a protein embodies at least three layers: the metal core, the ligand group, and the second shell, which is defined here to consist of all residues distant less than 3.5 angstrom from some ligand of the metal core. The ligands and second-shell residues can be characterized in terms of polarity, hydrophobicity, secondary structures, solvent accessibility, hydrogen-bonding interactions, and membership in statistically significant residue clusters of different kinds. Findings include the following: (i) Both histidine ligands of type I copper ions exclusively attach the Nδ 1nitrogen of the histidine imidazole ring to the metal, whereas histidine ligands for all mononuclear iron ions and nearly all type II copper ions are ligated via the Nε 2nitrogen. By contrast, multinuclear copper centers are coordinated predominantly by histidine Nε 2, whereas diiron histidine contacts are predominantly Nδ 1. Explanations in terms of steric differences between Nδ 1and Nε 2are considered. (ii) Except for blue copper (type I), the second-shell composition favors polar residues. (iii) For blue copper, the second shell generally contains multiple methionine residues, which are elements of a statistically significant histidine-cysteine-methionine cluster. Almost half of the second shell of blue copper consists of solvent-accessible residues, putatively facilitating electron transfer. (iv) Mononuclear copper atoms are never found with acidic carboxylate ligands, whereas single Mn2+ion ligands are predominantly acidic and the second shell tends to be mostly buried. (v) The extended environment of mononuclear Fe sites often is associated with histidine-tyrosine or histidine-acidic clusters.

This series provides inorganic chemists and materials scientists with a forum for critical, authoritative evaluations of advances in every area of the discipline.Volume 58 continues to report recent advances with a significant, up-to-date selection of contributions by internationally-recognized researchers.