Observation of a Cu(II)(2) (µ-1,2-peroxo)/Cu(III)(2) (µ-oxo)(2) equilibrium and its implications for copper-dioxygen reactivity.

Synthesis of small-molecule Cu2 O2 adducts has provided insight into the related biological systems and their reactivity patterns including the interconversion of the Cu(II) 2 (µ-η(2) :η(2) -peroxo) and Cu(III) 2 (µ-oxo)2 isomers. In this study, absorption spectroscopy, kinetics, and resonance Raman data show that the oxygenated product of [(BQPA)Cu(I) ](+) initially yields an "end-on peroxo" species, that subsequently converts to the thermodynamically more stable "bis-µ-oxo" isomer (Keq =3.2 at -90 °C). Calibration of density functional theory calculations to these experimental data suggest that the electrophilic reactivity previously ascribed to end-on peroxo species is in fact a result of an accessible bis-µ-oxo isomer, an electrophilic Cu2 O2 isomer in contrast to the nucleophilic reactivity of binuclear Cu(II) end-on peroxo species. This study is the first report of the interconversion of an end-on peroxo to bis-µ-oxo species in transition metal-dioxygen chemistry.

On the evolutionary significance and metal-binding characteristics of a monolobal transferrin from Ciona intestinalis.

Transferrins are a family of proteins that bind and transport Fe(III). Modern transferrins are typically bilobal and are believed to have evolved from an ancient gene duplication of a monolobal form. A novel monolobal transferrin, nicatransferrin (nicaTf), was identified in the primitive ascidian species Ciona intestinalis that possesses the characteristic features of the proposed ancestral Tf protein. In this work, nicaTf was expressed in Pichia pastoris. Extensive solution studies were performed on nicaTf, including UV-vis, fluorescence, CD, EPR and NMR spectroscopies, and electrospray time-of-flight mass spectrometry. The expressed protein is nonglycosylated, unlike the protein isolated from the organism. This property does not affect its ability to bind Fe(III). However, Fe(III)-bound nicaTf displays important spectral differences from other Fe(III)-bound transferrins, which are likely the consequence of differences in metal coordination. Coordination differences could also account for the weaker affinity of nicaTf for Fe(III) (log K = 18.5) compared with bilobal human serum transferrin (HsTf) (log K = 22.5 and 21.4). The Fe-nicaTf complex is not labile, as indicated by slow metal removal kinetics by the high-affinity chelator tiron at pH 7.4. The protein alternatively binds up to one equivalent of Ti(IV) or V(V), which suggests that it may transport nonferric metals. These solution studies provide insight into the structure and function of the primitive monolobal transferrin of C. intestinalis for comparison with higher order bilobal transferrins. They suggest that a major advantage for the evolution of modern transferrins, dominantly of bilobal form, is stronger Fe(III) affinity because of cooperativity.

Mono-, bi-, and trinuclear CuII-Cl containing products based on the tris(2-pyridylmethyl)amine chelate derived from copper(I) complex dechlorination reactions of chloroform.

The ligand TMPA (tris(2-pyridylmethyl)amine) and its copper complexes have played a prominent role in recent (bio)inorganic chemistry studies; the copper(I) complex [CuI(TMPA)(CH3CN)]+ possesses an extensive dioxygen reactivity, and it is also known to effect the reductive dechlorination of substrates such as dichloromethane and benzyl and allyl chlorides. In this report, we describe a set of new analogues of TMPA, ligand 6TMPAOH, binucleating Iso-DO, and trinucleating SYMM. Copper(I) complexes with these ligands and a previously described binucleating ligand DO react with chloroform, resulting in reductive dechlorination and production of [CuIIx(L)Clx]x+ (x = 1, 2, or 3). X-ray crystal structures of [CuII(6TMPAOH)Cl]PF6, [CuII2(Iso-DO)Cl2](PF6)2, [CuII2(DO)Cl2](PF6)2, and [Cu3(SYMM)Cl3](PF6)3 are presented, and the compounds are also characterized by UV-vis and EPR spectroscopies as well as cyclic voltammetry. The steric influence of a pyridyl 6-substituent (in the complexes with 6TMPAOH, Iso-DO, and SYMM) on the solid state and solution structures and redox potentials are compared and contrasted to those chlorocopper(II) complexes with a pyridyl 5'-substituent (in [CuII2(DO)Cl2](PF6)2 and in [CuII(TMPA)Cl]+). Some insights into the reductive dechlorination process have been obtained by using 2H NMR spectroscopy in following the reaction of [Cu2(Iso-DO)(CH3CN)2](PF6)2 with CDCl3, in the presence or absence of a radical trap, 2,4-di-tert-butylphenol.