pH-mediated manipulation of the histidine brace in LPMOs and generation of a tri-anionic variant, investigated by EPR, ENDOR, ESEEM and HYSCORE spectroscopy.

Lytic Polysaccharide Monooxygenases (LPMOs) catalyze the oxidative depolymerization of polysaccharides at a monocopper active site, that is coordinated by the so-called histidine brace. In the past, this motif has sparked considerable interest, mostly due to its ability to generate and stabilize highly oxidizing intermediates during catalysis. We used a variety of advanced EPR techniques, including Electron Nuclear Double Resonance (ENDOR), Electron Spin Echo Envelope Modulation (ESEEM) and Hyperfine Sublevel Correlation (HYSCORE) spectroscopy in combination with isotopic labelling (N, H) to characterize the active site of the bacterial LPMO AA10A over a wide pH range (pH 4.

Distinguishing between aquo and hydroxo coordination in molecular copper complexes by H and O ENDOR spectroscopy.

Aquo and hydroxo ligands play an essential role in the chemistry of many copper enzymes and small molecule catalysts. The formation of a series of copper complexes with HO and OH ligands in various positions, including [Cu(bpy)(OAc)(HO)] (Cu-I), [Cu(bpy)(OH)(HO)] (Cu-III), [Cu(OH)(HO)] (Cu-IV), [Cu(bpy)(HO)(HO)] (Cu-V) and [Cu(bpy)(HO)] (Cu-VI), were investigated through Electron Paramagnetic Resonance (EPR) and UV-Vis spectroscopy in aqueous copper bipyridine solutions in the dependence of the pH and the copper-to-bipyridine ratio (bpy = 2,2'-bipyridine). H- and O-enrichment of the copper complexes allowed us to determine the H and O nuclear hyperfine interactions of their HO ligands Q-band Electron Nuclear Double Resonance (ENDOR) spectroscopy.

Mutational dissection of a hole hopping route in a lytic polysaccharide monooxygenase (LPMO).

Oxidoreductases have evolved tyrosine/tryptophan pathways that channel highly oxidizing holes away from the active site to avoid damage. Here we dissect such a pathway in a bacterial LPMO, member of a widespread family of C-H bond activating enzymes with outstanding industrial potential. We show that a strictly conserved tryptophan is critical for radical formation and hole transference and that holes traverse the protein to reach a tyrosine-histidine pair in the protein's surface.

X-Band Parallel-Mode and Multifrequency Electron Paramagnetic Resonance Spectroscopy of = 1/2 Bismuth Centers.

The recent successes in the isolation and characterization of several bismuth radicals inspire the development of new spectroscopic approaches for the in-depth analysis of their electronic structure. Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for the characterization of main group radicals. However, the large electron-nuclear hyperfine interactions of Bi (Bi, = 9/2) have presented difficult challenges to fully interpret the spectral properties for some of these radicals.

Single-Electron Oxidation of Carbene-Coordinated Pnictinidenes-Entry into Heteroleptic Radical Cations and Metalloid Clusters.

Stable heavy main group element radicals are challenging synthetic targets. Although several strategies have been developed to stabilize such odd-electron species, the number of heavier pnictogen-centered radicals is limited. We report on a series of two-coordinated pnictogen-centered radical cations [(cAAC)EGa(Cl)L][B(CF)] (cAAC = [HC(CMe)NDipp]C; Dipp = 2,6--PrCH; E = As , Sb , Bi ; L = HC[C(Me)NDipp]) synthesized by one-electron oxidation of L(Cl)Ga-substituted pnictinidenes (cAAC)EGa(Cl)L (E = As , Sb , Bi ).

Sequential Reduction of Borylstibane to an Electronically Nonsymmetric Diboryldistibene Radical Anion.

Understanding the formation of metal-metal bonds and their electronic structures is still a scientific task. We herein report on the stepwise synthesis of boryl-substituted antimony compounds in which the antimony atoms adopt four different oxidation states (+III, +II, +I, +I/0). Sb-C bond homolysis of Cp*[(HCNDip)B]SbCl (; Cp* = CMe; Dip = 2,6-PrCH) gave diboryldichlorodistibane [(HCNDip)BSbCl] (), which reacted with KC to form diboryldistibene [(HCNDip)BSb] () and traces of cyclotetrastibane [(HCNDip)B]SbCl ().

Synthesis, structure and bonding nature of heavy dipnictene radical anions.

Cyclic voltammetry (CV) studies of two L(X)Ga-substituted dipnictenes [L(RN)GaE] (E = Sb, R = Me ; E = Bi; R = Et ; L = HC[C(Me)NDipp]; Dipp = 2,6--PrCH) showed reversible reduction events. Single electron reduction of and with KC in DME in the presence of benzo-18-crown-6 (B-18-C-6) gave the corresponding dipnictenyl radical anions (DME)[K(B-18-C-6)][L(RN)GaE] (E = Sb, R = Me ; E = Bi, R = Et ). Radical anions and were characterized by EPR, UV-vis and single crystal X-ray diffraction, while quantum chemical calculations gave deeper insight into the nature of the chemical bonding.