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.