Intramolecular Phenolic H-Atom Abstraction by a NArOH Ligand-Supported (μ-η:η-Peroxo)dicopper(II) Species Relevant to the Active Site Function of oxy-Tyrosinase.

Synthetic side-on peroxide-bound dicopper(II) () complexes are important for understanding the active site structure/function of many copper-containing enzymes. This work highlights the formation of new {Cu(μ-η:η-O)Cu} complexes (with electronic absorption and resonance Raman (rR) spectroscopic characterization) using tripodal NArOH ligands at -135 °C, which spontaneously participate in intramolecular phenolic H-atom abstraction (HAA). This results in the generation of bis(phenoxyl radical)bis(μ-OH)dicopper(II) intermediates, substantiated by their EPR/UV-vis/rR spectroscopic signatures and crystal structural determination of a diphenoquinone dicopper(I) complex derived from ligand -C═C coupling.

Reductive Coupling of Nitric Oxide by Cu(I): Stepwise Formation of Mono- and Dinitrosyl Species to a Cupric Hyponitrite Intermediate.

Transition-metal-mediated reductive coupling of nitric oxide (NO) to nitrous oxide (NO) has significance across the fields of industrial chemistry, biochemistry, medicine, and environmental health. Herein, we elucidate a density functional theory (DFT)-supplemented mechanism of NO reductive coupling at a copper-ion center, [(tmpa)Cu(MeCN)] () {tmpa = tris(2-pyridylmethyl)amine}. At -110 °C in EtOH (<-90 °C in MeOH), exposing to NO leads to a new binuclear hyponitrite intermediate [{(tmpa)Cu}(μ-NO)] (), exhibiting temperature-dependent irreversible isomerization to the previously characterized κ-O,O'--[(tmpa)Cu(μ-NO)] () complex.

A Thioether-Ligated Cupric Superoxide Model with Hydrogen Atom Abstraction Reactivity.

The central role of cupric superoxide intermediates proposed in hormone and neurotransmitter biosynthesis by noncoupled binuclear copper monooxygenases like dopamine-β-monooxygenase has drawn significant attention to the unusual methionine ligation of the Cu ("Cu") active site characteristic of this class of enzymes. The copper-sulfur interaction has proven critical for turnover, raising still-unresolved questions concerning Nature's selection of an oxidizable Met residue to facilitate C-H oxygenation. We describe herein a model for Cu, [(NS)Cu] ([]), and its O-bound analog [(NS)Cu(O)] ([·O]).

Kβ X-ray Emission Spectroscopy as a Probe of Cu(I) Sites: Application to the Cu(I) Site in Preprocessed Galactose Oxidase.

Cu(I) active sites in metalloproteins are involved in O activation, but their O reactivity is difficult to study due to the Cu(I) d closed shell which precludes the use of conventional spectroscopic methods. Kβ X-ray emission spectroscopy (XES) is a promising technique for investigating Cu(I) sites as it detects photons emitted by electronic transitions from occupied orbitals. Here, we demonstrate the utility of Kβ XES in probing Cu(I) sites in model complexes and a metalloprotein.

Copper(I) Complex Mediated Nitric Oxide Reductive Coupling: Ligand Hydrogen Bonding Derived Proton Transfer Promotes NO Release.

A cuprous chelate bearing a secondary sphere hydrogen bonding functionality, [(PV-tmpa)Cu], transforms NO to NO in high-yields in methanol. Ligand derived proton transfer facilitates N-O bond cleavage of a putative hyponitrite intermediate releasing NO, underscoring the crucial balance between H-bonding capabilities and acidities in (bio)chemical NO coupling systems.

Impact of Intramolecular Hydrogen Bonding on the Reactivity of Cupric Superoxide Complexes with O-H and C-H Substrates.

The dioxygen reactivity of a series of TMPA-based copper(I) complexes (TMPA=tris(2-pyridylmethyl)amine), with and without secondary-coordination-sphere hydrogen-bonding moieties, was studied at -135 °C in 2-methyltetrahydrofuran (MeTHF). Kinetic stabilization of the H-bonded [( TMPA)Cu (O )] cupric superoxide species was achieved, and they were characterized by resonance Raman (rR) spectroscopy. The structures and physical properties of [( TMPA)Cu (N )] azido analogues were compared, and the O reactivity of ligand-Cu complexes when an H-bonding moiety is replaced by a methyl group was contrasted.

Intramolecular Hydrogen Bonding Enhances Stability and Reactivity of Mononuclear Cupric Superoxide Complexes.

[(L)Cu(O)] (i.e., cupric-superoxo) complexes, as the first and/or key reactive intermediates in (bio)chemical Cu-oxidative processes, including in the monooxygenases PHM and DβM, have been systematically stabilized by intramolecular hydrogen bonding within a TMPA ligand-based framework.

Efficient and simple approaches towards direct oxidative esterification of alcohols.

The present article describes novel oxidative protocols for direct esterification of alcohols. The protocols involve successful demonstrations of both "cross" and "self" esterification of a wide variety of alcohols. The cross-esterification proceeds under a simple transition-metal-free condition, containing catalytic amounts of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy)/TBAB (tetra-n-butylammonium bromide) in combination with oxone (potassium peroxo monosulfate) as the oxidant, whereas the self-esterification is achieved through simple induction of Fe(OAc)2 /dipic (dipic=2,6-pyridinedicarboxylic acid) as the active catalyst under an identical oxidizing environment.