Susan Kaderli

Reversible cleavage and formation of the dioxygen O-O bond within a dicopper complex

A key step in dioxygen evolution during photosynthesis is the oxidative generation of the O-O bond from water by a manganese cluster consisting of M2(μ-O)2 units (where M is manganese). The reverse reaction, reductive cleavage of the dioxygen O-O bond, is performed at a variety of dicopper and di-iron active sites in enzymes that catalyze important organic oxidations. Both processes can be envisioned to involve the interconversion of dimetal-dioxygen adducts, M2(O2), and isomers having M2(μ-O)2 cores. The viability of this notion has been demonstrated by the identification of an equilibrium between synthetic complexes having [Cu2(μ-η2:η2-O2)]2+ and [Cu2(μ-O)2]2+ cores through kinetic, spectroscopic, and crystallographic studies.

Second order global analysis: the evaluation of series of spectrophotometric titrations for improved determination of equilibrium constants

Abstract In spectrophotometric titrations, linear or near-linear dependence of concentration profiles and the existence of minor species cause difficulties in the evaluation of the data. In the first case calculated absorption spectra and in the second case the corresponding equilibrium constants are not or only poorly defined. The result is the inability to reliably fit a reasonable model to the data. In second order global analysis, a number of spectrophotometric titrations with different initial concentrations are simultaneously analysed. In this way the concentration matrix is augmented to full rank and, secondly, conditions for the significant formation of each species can be obtained. Resulting equilibrium constants and absorption spectra are notably better defined. EQUISPEC is a computer program using the matrix based MATLAB environment for second order global analysis of spectrophotometric equilibrium data. It has been successfully tested with generated data and shown to overcome linear dependence and reproduce reported stability constants for the zinc: 1,10-phenanthroline system and to considerably improve the analysis of the complexation of Cu 2+ by diethylenetriamine (dien).

Superoxo, μ-peroxo, and μ-oxo complexes from heme/O2 and heme-Cu/O2 reactivity: Copper ligand influences in cytochrome c oxidase models

The O2-reaction chemistry of 1:1 mixtures of (F8)FeII (1; F8 = tetrakis(2,6-diflurorophenyl)porphyrinate) and [(LMe2N)CuI]+ (2; LMe2N = N,N-bis{2-[2-(N′,N′-4-dimethylamino)pyridyl]ethyl}methylamine) is described, to model aspects of the chemistry occurring in cytochrome c oxidase. Spectroscopic investigations, along with stopped-flow kinetics, reveal that low-temperature oxygenation of 1/2 leads to rapid formation of a heme-superoxo species (F8)FeIII-(O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{-}}}\end{equation*}\end{document}) (3), whether or not 2 is present. Complex 3 subsequently reacts with 2 to form [(F8)FeIII–(O\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} \begin{equation*}{\mathrm{_{2}^{2-}}}\end{equation*}\end{document})–CuII(LMe2N)]+ (4), which thermally converts to [(F8)FeIII–(O)–CuII(LMe2N)]+ (5), which has an unusually bent (Fe–O–Cu) bond moiety. Tridentate chelation, compared with tetradentate, is shown to dramatically lower the ν(O–O) values observed in 4 and give rise to the novel structural features in 5.

Kinetic and thermodynamic parameters of copper-dioxygen interaction with different oxygen binding modes

Abstract Kinetic and thermodynamic parameters for metal ion-O 2 interaction have been obtained for a variety of copper(I) complexes with different binding modes for dioxygen. In general, favorable binding enthalpies of up to 80 kJ mol −1 are compensated by strongly negative reaction entropies up to −220 J K −1 mol −1 , restricting the range of overall stabilities. Sequential formation of superoxo and peroxo complexes, as well as concomitant formation of η 1 : η 1 and η 2 : η 2 μ-peroxo complexes has been established by low-temperature stopped-flow experiments. In several cases, pseudoreversible binding of dioxygen is followed by an irreversible oxidation of the organic ligand. A recent result is the identification of a rapid equilibrium between an η 2 : η 2 μ-peroxo complex and the isomeric bis-μ-oxo compound with broken OO bond which may be fundamental to several O 2 dependent redox enzymes.

Dioxygen mediated oxo-transfer to an amine and oxidative N-dealkylation chemistry with a dinuclear copper complex

Reaction of dioxygen with a dinuclear copper(I) complex of a new binucleating ligand is described, wherein a peroxo–dicopper(II) (Cu2–O2) intermediate leads to an oxo-transfer reaction to give an N-oxide of an N-benzyl internal ligand substrate; additionally observed regioselective oxidative N-dealkylation chemistry occurs.

Copper dioxygen complexes stable at ambient temperature:optimization of ligand design and solvent

Entropic destabilization of low-molecular mass µ-peroxodicopper(II) complexes are overcome using a new binucleating open-chain ligand by the combination of an optimized linking unit with a less competing solvent; complete formation and satisfactory stability at room temperature are thus obtained.