Electrocatalytic Anaerobic Oxidation of Benzylic Amines Enabled by Ferrocene-Based Redox Mediators.

The generation and functionalization of carbon- or nitrogen-centered radicals are of great interest for their potential synthetic utility. Here, we report the anaerobic electrocatalytic oxidation of two primary benzylic amines, benzylamine and 2-picolylamine, in the presence of a catalytic quantity of an electron deficient ferrocene derivative as a single-electron redox mediator. The use of the appropriate redox mediator prevented fouling of the electrode surface and significantly decreased the potential at which the catalytic oxidation reaction occurred.

Series of Protonated Nitrogen Bases with a Weakly Coordinating Counteranion: Observation of the N-H Spin-Spin Coupling.

A distinguished triplet splitting pattern for the N-H couplings in the proton signals of a series of protonated nitrogen bases-aliphatic and aromatic amines, as well as pyridines-with the weakly coordinating tetrakis(pentafluorophenyl)borate anion, [B(CF)], is observed for the first time in nonaqueous media at room temperature. The effects of ion pairing, solvent parameters, and correlation between the δ, , and p values are reported.

Insights into the Chemical Diversity of Selected Fungi from the Tza Itzá Cenote of the Yucatan Peninsula.

Cenotes are habitats with unique physical, chemical, and biological features. Unexplored microorganisms from these sinkholes represent a potential source of bioactive molecules. Thus, a series of cultivable fungi ( spp.

New Terpenoids from the Corticioid Fungus Punctularia atropurpurascens and their Antimycobacterial Evaluation.

Chemical investigation of strain HM1 (Punctulariaceae), a corticioid isolated from a decorticated piece of bark collected in Bosque de Tlalpan, Mexico City, led to the isolation of a new drimane, 1--hydroxy-isodrimenine (1: ) and a new tetrahydroxy kauranol, 16-hydroxy-phlebia--kauranol (2: ), together with the known -phenylacetamide (3: ). Structures of all compounds were elucidated by spectroscopic and spectrometric methods, and the absolute configuration of 1: and 2: was confirmed via single-crystal X-ray crystallography. The isolated compounds showed modest antimycobacterial activity.

Dioxygen Reactivity of Copper(I)/Manganese(II)-Porphyrin Assemblies: Mechanistic Studies and Cooperative Activation of O.

The oxidation of transition metals such as manganese and copper by dioxygen (O) is of great interest to chemists and biochemists for fundamental and practical reasons. In this report, the O reactivities of 1:1 and 1:2 mixtures of [(TPP)Mn] (; TPP: Tetraphenylporphyrin) and [(tmpa)Cu(MeCN)] (; TMPA: Tris(2-pyridylmethyl)amine) in 2-methyltetrahydrofuran (MeTHF) are described. Variable-temperature (-110 °C to room temperature) absorption spectroscopic measurements support that, at low temperature, oxygenation of the (TPP)Mn/Cu mixtures leads to rapid formation of a cupric superoxo intermediate, [(tmpa)Cu(O)] (), independent of the presence of the manganese porphyrin complex ().

Structural Diversity of Perylenequinones Is Driven by Their Redox Behavior.

Hypocrellins and hypomycins are two subclasses of fungal perylenequinones with unique structural, biological, and photochemical properties. With the growing interest in these naturally occurring photosensitizers, more studies were warranted to better understand the structural relationships between these two subclasses of perylenequinones. In this study, the long-postulated biosynthetic precursor () of class B fungal perylenequinones was isolated and characterized from a -like sp.

Protonation of the oxo-bridged heme/copper assemblies: Modeling the oxidized state of the cytochrome c oxidase active site.

In this study on model compounds for the resting oxidized state of the iron‑copper binuclear center in cytochrome c oxidase (CcO), we describe the synthesis of a new μ-oxo-heme/Cu complex, [(TPP)Fe-O-Cu(tmpa)][B(CF)] (2) {TPP: tetraphenyl porphyrinate(2-); TMPA: tris(2-pyridylmethylamine)}, as well as two protonation events for three μ-oxo-heme/Cu complexes with varying peripheral substituents on the heme site. The addition of increasing amounts of strong acid to these μ-oxo-heme/Cu systems successively led to the generation of the corresponding μ-hydroxo, μ-aquo, and the dissociated complexes. The heme/Cu assemblies bridged through a water ligand are reported here for the first time and the H NMR and F NMR spectral properties are consistent with antiferromagnetically coupled high-spin iron(III) and copper(II) centers.

Proton Relay in Iron Porphyrins for Hydrogen Evolution Reaction.

The efficiency of the hydrogen evolution reaction (HER) can be facilitated by the presence of proton-transfer groups in the vicinity of the catalyst. A systematic investigation of the nature of the proton-transfer groups present and their interplay with bulk proton sources is warranted. The HERs electrocatalyzed by a series of iron porphyrins that vary in the nature and number of pendant amine groups are investigated using proton sources whose p values vary from ∼9 to 15 in acetonitrile.

Synthetic, spectroscopic, structural, and electrochemical investigations of ferricenium derivatives with weakly coordinating anions: ion pairing, substituent, and solvent effects.

A facile and effective strategy for the preparation of a series of ferricenium complexes bearing either electron-donating or electron-withdrawing substituents with weakly coordinating anions such as [B(C6F5)4]- or SbF6- is reported. These systems were thoroughly investigated for their ground state electronic structures in both solution and solid states using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopies as well as single crystal X-ray crystallography and electrochemical measurements. The X-ray structures of the six electron-deficient ferricenium derivatives are of particular interest as only a handful (∼5) of such derivatives have been structurally characterized to date.

The Chemistry of Kratom []: Updated Characterization Data and Methods to Elucidate Indole and Oxindole Alkaloids.

Two separate commercial products of kratom [ (Korth.) Havil. Rubiaceae] were used to generate reference standards of its indole and oxindole alkaloids.

Copper(I)/NO Reductive Coupling Producing a trans-Hyponitrite Bridged Dicopper(II) Complex: Redox Reversal Giving Copper(I)/NO Disproportionation.

A copper complex, [Cu(tmpa)(MeCN)], effectively reductively couples NO at RT in methanol (MeOH), giving a structurally characterized hyponitrito-dicopper(II) adduct. Hydrogen-bonding from MeOH is critical for the hyponitrite complex formation and stabilization. This complex exhibits the reverse redox process in aprotic solvents, giving Cu + NO, leading to Cu-mediated NO-disproportionation.

Electrocatalytic O2-Reduction by Synthetic Cytochrome c Oxidase Mimics: Identification of a "Bridging Peroxo" Intermediate Involved in Facile 4e(-)/4H(+) O2-Reduction.

A synthetic heme-Cu CcO model complex shows selective and highly efficient electrocatalytic 4e(-)/4H(+) O2-reduction to H2O with a large catalytic rate (>10(5) M(-1) s(-1)). While the heme-Cu model (FeCu) shows almost exclusive 4e(-)/4H(+) reduction of O2 to H2O (detected using ring disk electrochemistry and rotating ring disk electrochemistry), when imidazole is bound to the heme (Fe(Im)Cu), this same selective O2-reduction to water occurs only under slow electron fluxes. Surface enhanced resonance Raman spectroscopy coupled to dynamic electrochemistry data suggests the formation of a bridging peroxide intermediate during O2-reduction by both complexes under steady state reaction conditions, indicating that O-O bond heterolysis is likely to be the rate-determining step (RDS) at the mass transfer limited region.

Synthetic heme/copper assemblies: toward an understanding of cytochrome c oxidase interactions with dioxygen and nitrogen oxides.

Our long-time niche in synthetic biological inorganic chemistry has been to design ligands and generate coordination complexes of copper or iron ions or both, those reacting with dioxygen (O2) or nitrogen oxides (e.g., nitric oxide (NO(g)) and nitrite (NO2(-))) or both.

Nitrogen Oxide Atom-Transfer Redox Chemistry; Mechanism of NO(g) to Nitrite Conversion Utilizing μ-oxo Heme-Fe(III)-O-Cu(II)(L) Constructs.

While nitric oxide (NO, nitrogen monoxide) is a critically important signaling agent, its cellular concentrations must be tightly controlled, generally through its oxidative conversion to nitrite (NO2(-)) where it is held in reserve to be reconverted as needed. In part, this reaction is mediated by the binuclear heme a3/CuB active site of cytochrome c oxidase. In this report, the oxidation of NO(g) to nitrite is shown to occur efficiently in new synthetic μ-oxo heme-Fe(III)-O-Cu(II)(L) constructs (L being a tridentate or tetradentate pyridyl/alkylamino ligand), and spectroscopic and kinetic investigations provide detailed mechanistic insights.

Nitric oxide generation from heme/copper assembly mediated nitrite reductase activity.

Nitric oxide (NO) as a cellular signaling molecule and vasodilator regulates a range of physiological and pathological processes. Nitrite (NO2 (-)) is recycled in vivo to generate nitric oxide, particularly in physiologic hypoxia and ischemia. The cytochrome c oxidase binuclear heme a 3/CuB active site is one entity known to be responsible for conversion of cellular nitrite to nitric oxide.

Heme/copper assembly mediated nitrite and nitric oxide interconversion.

The heme(a3)/Cu(B) active site of cytochrome c oxidase is responsible for cellular nitrite reduction to nitric oxide; the same center can return NO to the nitrite pool via oxidative chemistry. Here, we show that a partially reduced heme/Cu assembly reduces NO(2)(-) ion, producing nitric oxide. The heme serves as the reductant, but the Cu(II) ion is also required.