Kβ X-ray Emission Spectroscopy of Cu(I)-Lytic Polysaccharide Monooxygenase: Direct Observation of the Frontier Molecular Orbital for HO Activation.

Lytic polysaccharide monooxygenases (LPMOs) catalyze the degradation of recalcitrant carbohydrate polysaccharide substrates. These enzymes are characterized by a mononuclear Cu(I) active site with a three-coordinate T-shaped "His-brace" configuration including the N-terminal histidine and its amine group as ligands. This study explicitly investigates the electronic structure of the d Cu(I) active site in a LPMO using Kβ X-ray emission spectroscopy (XES).

Fenton-like Chemistry by a Copper(I) Complex and HO Relevant to Enzyme Peroxygenase C-H Hydroxylation.

Lytic polysaccharide monooxygenases have received significant attention as catalytic convertors of biomass to biofuel. Recent studies suggest that its peroxygenase activity (i.e.

Particle Swarm Fitting of Spin Hamiltonians: Magnetic Circular Dichroism of Reduced and NO-Bound Flavodiiron Protein.

A particle swarm optimization (PSO) algorithm is described for the fitting of ground-state spin Hamiltonian parameters from variable-temperature/variable-field (VTVH) magnetic circular dichroism (MCD) data. This PSO algorithm is employed to define the ground state of two catalytic intermediates from a flavodiiron protein (FDP), a class of enzymes with nitric oxide reductase activity. The bimetallic iron active site of this enzyme proceeds through a biferrous intermediate and a mixed ferrous-{FeNO} intermediate during the catalytic cycle, and the MCD spectra of these intermediates are presented and analyzed.

The three-spin intermediate at the O-O cleavage and proton-pumping junction in heme-Cu oxidases.

Understanding the mechanistic coupling of molecular oxygen reduction and proton pumping for adenosine triphosphate synthesis during cellular respiration is the primary goal of research on heme-copper oxidases—the terminal complex in the membrane-bound electron transport chain. Cleavage of the oxygen-oxygen bond by the heme-copper oxidases forms the key intermediate P, which initiates proton pumping. This intermediate is now experimentally defined by variable-temperature, variable-field magnetic circular dichroism spectroscopy on a previously unobserved excited state feature associated with its heme iron(IV)-oxo center.

P NMR Chemical Shift Tensors: Windows into Ruthenium Phosphinidene Complex Electronic Structures.

A series of octamethylcalix[4]pyrrole/ruthenium phosphinidene complexes (Na[=PR]) can be accessed by phosphinidene transfer from the corresponding RP ( = CH, anthracene) compounds (R = Bu, Pr, OEt, NH, NMe, NEt, NPr, N, dimethylpiperidino). Isolation of the -butyl and dimethylamino derivatives allowed comparative studies of their P nuclear shielding tensors by magic-angle-spinning solid-state nuclear magnetic resonance spectroscopy. Density functional theory and natural chemical shielding analyses reveal the relationship between the P chemical shift tensor and the local ruthenium/phosphorus electronic structure.

An Azophosphine Synthetic Equivalent of Mesitylphosphaazide and Its 1,3-Dipolar Cycloaddition Reactions.

Dibenzo-7-phosphanorbornadiene-substituted diazene MesNP (, where Mes = mesityl, = anthracene, or CH), a synthetic equivalent of mesitylphosphaazide (MesNP) and anthracene, was synthesized by treatment of [PhBP][Na(OEt)] with [MesN]OTf (OTf = CFSO) in thawing tetrahydrofuran (14% isolated yield). Treatment of with unsaturated molecules cyclooctyne, [Na(dioxane)][OCP] (phosphaethynolate), and Ad-C≡P (Ad = adamantyl) results in the corresponding [3 + 2] phosphaazide-(phospha)alkyne cycloadducts, with concomitant loss of anthracene in 65%, 49%, and 38% isolated yield, respectively. Structural data for the phosphaethynolate cycloadduct ([][Na(12-crown-4)]) were obtained in a single-crystal X-ray diffraction study.

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]).

Kinetic analysis of amino acid radicals formed in HO-driven Cu LPMO reoxidation implicates dominant homolytic reactivity.

Lytic polysaccharide monooxygenases (LPMOs) have been proposed to react with both [Formula: see text] and [Formula: see text] as cosubstrates. In this study, the [Formula: see text] reaction with reduced LPMO9A (Cu-LPMO9A) is demonstrated to be 1,000-fold faster than the [Formula: see text] reaction while producing the same oxidized oligosaccharide products. Analysis of the reactivity in the absence of polysaccharide substrate by stopped-flow absorption and rapid freeze-quench (RFQ) electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) yields two intermediates corresponding to neutral tyrosyl and tryptophanyl radicals that are formed along minor reaction pathways.

Isolation of an elusive phosphatetrahedrane.

This exploratory synthesis investigation was undertaken to determine the viability of replacing a single carbon vertex with another p-block element in a highly strained tetrahedrane molecule. Phosphorus was selected for this purpose because the stable molecular form of elemental phosphorus is tetrahedral. Our synthetic strategy was to generate an unsaturated phosphorus center bonded to a substituted cyclopropenyl group, a situation that could lead to closure to provide the desired phosphatetrahedrane framework.

Organoiron- and Fluoride-Catalyzed Phosphinidene Transfer to Styrenic Olefins in a Stereoselective Synthesis of Unprotected Phosphiranes.

Catalytic phosphiranation has been achieved, allowing preparation of -1-R-2-phenylphosphiranes (R = -Bu: --Bu; -Pr: --Pr) from the corresponding dibenzo-7-(R)-7-phospha-norbornadiene (RP, = CH, anthracene) and styrene in 73% and 57% isolated yields, respectively. The cocatalyst system requires tetramethylammonium fluoride (TMAF) and [Fp(THF)][BF] (Fp = Fe(η-CH)(CO)). In the case of the -Bu derivative, the reaction mechanism was probed using stoichiometric reaction studies, a Hammett analysis, and a deuterium labeling experiment.

Orthophosphate and Sulfate Utilization for C-E (E = P, S) Bond Formation via Trichlorosilyl Phosphide and Sulfide Anions.

Reduction of phosphoric acid (HPO) or tetra- n-butylammonium bisulfate ([TBA][HSO]) with trichlorosilane leads to the formation of the bis(trichlorosilyl)phosphide ([P(SiCl)], 1) and trichlorosilylsulfide ([ClSiS], 2) anions, respectively. Balanced equations for the formation of the TBA salts of anions 1 and 2 were formulated based on the identification of hexachlorodisiloxane and hydrogen gas as byproducts arising from these reductive processes: i) [HPO] + 10HSiCl → 1 + 4O(SiCl) + 6H for P and ii) [HSO] + 9HSiCl → 2 + 4O(SiCl) + 5H for S. Hydrogen gas was identified by its subsequent use to hydrogenate an alkene ((-)-terpinen-4-ol) using Crabtree's catalyst ([(COD)Ir(py)(PCy)][PF], COD = 1,5-cyclooctadiene, py = pyridine, Cy = cyclohexyl).

Anthracene as a Launchpad for a Phosphinidene Sulfide and for Generation of a Phosphorus-Sulfur Material Having the Composition PS, a Vulcanized Red Phosphorus That Is Yellow.

Thermolysis of a pair of dibenzo-7-phosphanorbornadiene compounds is shown to lead to differing behaviors: phosphinidene sulfide release and formation of amorphous PS. These compounds, BuP(S)A (1, A = CH or anthracene; 59% isol. yield) and HP(S)A (2; 63%), are available through thionation of BuPA and the new secondary phosphine HPA (5), prepared from MeNPA and DIBAL-H in 50% yield.

Synthetic and Spectroscopic Investigations Enabled by Modular Synthesis of Molecular Phosphaalkyne Precursors.

A series of dibenzo-7-phosphanorbornadiene compounds, PhPC(R)PA (1-R; A = CH, anthracene; R = Me, Et, Pr, Bu), are reported to be capable of thermal fragmentation to generate alkyl-substituted phosphaalkynes (RC≡P) concomitant with triphenylphosphine and anthracene. Facile preparation of these molecular precursors proceeds by treatment of ClPA with the appropriate ylide PhP═CHR (2 equiv). For methyl, ethyl, and isopropyl substituents, the phosphaalkyne conversions are measured to be 56-73% in solution by quantitative P NMR spectroscopy.

Sulfur monoxide thermal release from an anthracene-based precursor, spectroscopic identification, and transfer reactivity.

Sulfur monoxide (SO) is a highly reactive molecule and thus, eludes bulk isolation. We report here on synthesis and reactivity of a molecular precursor for SO generation, namely 7-sulfinylamino-7-azadibenzonorbornadiene (). This compound has been shown to fragment readily driven by dinitrogen expulsion and anthracene formation on heating in the solid state and in solution, releasing SO at mild temperatures (<100 °C).

Diazomethane umpolung atop anthracene: an electrophilic methylene transfer reagent.

Formal addition of diazomethane's terminal nitrogen atom to the 9,10-positions of anthracene yields HCN (, = CH or anthracene). The synthesis of this hydrazone is reported from Carpino's hydrazine HN through treatment with paraformaldehyde. Compound has been found to be an easy-to-handle solid that does not exhibit dangerous heat or shock sensitivity.

An exploding N-isocyanide reagent formally composed of anthracene, dinitrogen and a carbon atom.

Targeted as an example of a compound composed of a carbon atom together with two stable neutral leaving groups, 7-isocyano-7-azadibenzonorbornadiene, CNA (1, A = CH or anthracene) has been synthesized and spectroscopically and structurally characterized. The terminal C atom of 1 can be transferred: mesityl nitrile oxide reacts with 1 to produce carbon monoxide, likely via intermediacy of the N-isocyanate OCNA. Reaction of 1 with [RuCl(CO)(PCy)] leads to [RuCl(CO)(1)(PCy)] which decomposes unselectively: in the product mixture, the carbide complex [RuCl(C)(PCy)] was detected.

Terminal tungsten pnictide complex formation through pnictaethynolate decarbonylation.

Tungsten(iv) tetrakis(2,6-diisopropylphenoxide) (1) has been demonstrated to be a competent platform for decarbonylative formation of anionic terminal pnictide complexes upon treatment with pnictaethynolate anions: cyanate, 2-phosphaethynolate, and 2-arsaethynolate. These transformations constitute the first examples of terminal phosphide and arsenide complex formation at a transition metal center from OCP and OCAs, respectively. The phosphide and arsenide complexes are also the first to be isolated in a tetragonal, all-oxygen ligand environment.

Mechanism and Scope of Phosphinidene Transfer from Dibenzo-7-phosphanorbornadiene Compounds.

Dibenzo-7-phosphanorbornadiene compounds, RPA (A = CH or anthracene), are investigated as phosphinidene sources upon thermally induced (70-90 °C) anthracene elimination. Analysis of substituent effects reveals that π-donating dialkylamide groups are paramount to successful phosphinidene transfer; poorer π-donors give reduced or no transfer. Substituent steric bulk is also implicated in successful transfer.

Spectroscopic Characterization, Computational Investigation, and Comparisons of ECX (E = As, P, and N; X = S and O) Anions.

Three newly synthesized [Na(221-Kryptofix)] salts containing AsCO, PCO, and PCS anions were successfully electrosprayed into a vacuum, and these three ECX anions were investigated by negative ion photoelectron spectroscopy (NIPES) along with high-resolution photoelectron imaging spectroscopy. For each ECX anion, a well-resolved NIPE spectrum was obtained, in which every major peak is split into a doublet. The splittings are attributed to spin-orbit coupling (SOC) in the ECX radicals.

Phosphinidene Reactivity of a Transient Vanadium P≡N Complex.

Toward the preparation of a coordination complex of the heterodiatomic molecule PN, P≡N-V(N[Bu]Ar) (1, Ar = 3,5-MeCH), we report the use of ClPA (A = CH, anthracene) as a formal source of phosphorus(I) in its reaction with Na[NV(N[Bu]Ar)] (Na[4]) to yield trimeric cyclo-triphosphane [PNV(N[Bu]Ar)] (3) with a core composed exclusively of phosphorus and nitrogen. In the presence of NapS (peri-1,8-naphthalene disulfide), NapSP-NV(N[Bu]Ar) (6) is instead generated in 80% yield, suggesting trapping of transient 1. Upon mild heating, 3 readily fragments into dimeric [PNV(N[Bu]Ar)] (2), while in the presence of bis(trimethylsilyl)acetylene or cis-4-octene, the respective phosphirene (Ar[Bu]N)VN-PC(SiMe) (7) or phosphirane (Ar[Bu]N)VN-P(CH) (8) compounds are generated.

A Joint Experimental and Computational Study of the Negative Ion Photoelectron Spectroscopy of the 1-Phospha-2,3,4-triazolate Anion, HCPN3(.).

We report here the results of a combined experimental and computational study of the negative ion photoelectron spectroscopy (NIPES) of the recently synthesized, planar, aromatic, HCPN3(-) ion. The adiabatic electron detachment energy of HCPN3(-) (electron affinity of HCPN3(•)) was measured to be 3.555 ± 0.

Highly Fluorinated Ir(III)-2,2':6',2″-Terpyridine-Phenylpyridine-X Complexes via Selective C-F Activation: Robust Photocatalysts for Solar Fuel Generation and Photoredox Catalysis.

A series of fluorinated Ir(III)-terpyridine-phenylpyridine-X (X = anionic monodentate ligand) complexes were synthesized by selective C-F activation, whereby perfluorinated phenylpyridines were readily complexed. The combination of fluorinated phenylpyridine ligands with an electron-rich tri-tert-butyl terpyridine ligand generates a "push-pull" force on the electrons upon excitation, imparting significant enhancements to the stability, electrochemical, and photophysical properties of the complexes. Application of the complexes as photosensitizers for photocatalytic generation of hydrogen from water and as redox photocatalysts for decarboxylative fluorination of several carboxylic acids showcases the performance of the complexes in highly coordinating solvents, in some cases exceeding that of the leading photosensitizers.

Negative ion photoelectron spectroscopy of PN: electron affinity and electronic structures of PN˙.

We report here a negative ion photoelectron spectroscopy (NIPES) and study of the recently synthesized planar aromatic inorganic ion PN, to investigate the electronic structures of PN and its neutral PN˙ radical. The adiabatic detachment energy of PN (electron affinity of PN˙) was determined to be 3.765 ± 0.

A Molecular Precursor to Phosphaethyne and Its Application in Synthesis of the Aromatic 1,2,3,4-Phosphatriazolate Anion.

Dibenzo-7-phosphanorbornadiene Ph3PC(H)PA (1, A = C14H10, anthracene) is reported here as a molecular precursor to phosphaethyne (HC≡P), produced together with anthracene and triphenylphosphine. HCP generated by thermolysis of 1 has been observed by molecular beam mass spectrometry, laser-induced fluorescence, microwave spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy. In toluene, fragmentation of 1 has been found to proceed with activation parameters of ΔH(⧧) = 25.

[Ir(N^N^N)(C^N)L]+: a new family of luminophores combining tunability and enhanced photostability.

The relatively unexplored luminophore architecture [Ir(N^N^N)(C^N)L](+) (N^N^N = tridentate polypyridyl ligand, C^N = 2-phenylpyridine derivative, and L = monodentate anionic ligand) offers the stability of tridentate polypyridyl coordination along with the tunability of three independently variable ligands. Here, a new family of these luminophores has been prepared based on the previously reported compound [Ir(tpy)(ppy)Cl](+) (tpy = 2,2':6',2″-terpyridine and ppy = 2-phenylpyridine). Complexes are obtained as single stereoisomers, and ligand geometry is unambiguously assigned via X-ray crystallography.