A Four-Coordinate End-On Superoxocopper(II) Complex: Probing the Link between Coordination Number and Reactivity.

Although the reactivity of five-coordinate end-on superoxocopper(II) complexes, Cu(η-O), is dominated by hydrogen atom transfer, the majority of four-coordinate Cu(η-O) complexes published thus far display nucleophilic reactivity. To investigate the origin of this difference, we have developed a four-coordinate end-on superoxocopper(II) complex supported by a sterically encumbered bis(2-pyridylmethyl)amine ligand, dpb-BPA (), and compared its substrate reactivity with that of a five-coordinate end-on superoxocopper(II) complex ligated by a similarly substituted tris(2-pyridylmethyl)amine, dpb-TMPA (). Kinetic isotope effect (KIE) measurements and correlation of second-order rate constants ('s) versus oxidation potentials () for a range of phenols indicates that the complex [Cu(η-O)()] reacts with phenols via a similar hydrogen atom transfer (HAT) mechanism to [Cu(η-O)()].

Determination of the iron(IV) local spin states of the Q intermediate of soluble methane monooxygenase by Kβ X-ray emission spectroscopy.

Soluble methane monooxygenase (sMMO) facilitates the conversion of methane to methanol at a non-heme Fe intermediate MMOH, which is formed in the active site of the sMMO hydroxylase component (MMOH) during the catalytic cycle. Other biological systems also employ high-valent Fe sites in catalysis; however, MMOH is unique as Nature's only identified Fe intermediate. Previous Fe Mössbauer spectroscopic studies have shown that MMOH employs antiferromagnetic coupling of the two Fe sites to yield a diamagnetic cluster.

Phosphorus Kβ X-ray emission spectroscopy detects non-covalent interactions of phosphate biomolecules .

Phosphorus is ubiquitous in biochemistry, being found in the phosphate groups of nucleic acids and the energy-transferring system of adenine nucleotides ( ATP). Kβ X-ray emission spectroscopy (XES) of phosphorus has been largely unexplored, with no previous applications to biomolecules. Here, the potential of P Kβ XES to study phosphate-containing biomolecules, including ATP and NADPH, is evaluated, as is the application of the technique to aqueous solution samples.

Probing a Silent Metal: A Combined X-ray Absorption and Emission Spectroscopic Study of Biologically Relevant Zinc Complexes.

As the second most common transition metal in the human body, zinc is of great interest to research but has few viable routes for its direct structural study in biological systems. Herein, Zn valence-to-core X-ray emission spectroscopy (VtC XES) and Zn K-edge X-ray absorption spectroscopy (XAS) are presented as a means to understand the local structure of zinc in biological systems through the application of these methods to a series of biologically relevant molecular model complexes. Taken together, the Zn K-edge XAS and VtC XES provide a means to establish the ligand identity, local geometry, and metal-ligand bond lengths.