Thin-film water oxidation catalysts (Co−Pi) prepared by electrodeposition from phosphate electrolyte and Co(NO3)2 have been characterized electron paramagnetic resonance (EPR) spectroscopy. Co−Pi catalyst films exhibit EPR signals corresponding to populations of both Co(II) Co(IV). As the deposition voltage is increased into region where prevails, population Co(IV) rises decreases. The changes in redox speciation film can also be induced, part, prolonged catalysis absence additional...

The laboratory synthesis of the oxygen-evolving complex (OEC) photosystem II has been objective synthetic chemists since early 1970s. However, absence structural information on OEC hampered these efforts. Crystallographic reports that have appearing at ever-improving resolution over past ten years finally provided invaluable and show it comprises a [Mn 3 CaO 4 ] distorted cubane, to which is attached fourth, external Mn atom, whole unit polypeptides primarily by aspartate glutamate...

Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co(4)O(4)(C(5)H(5)N)(4)(CH(3)CO(2))(4)](+) (1(+)), a cobalt tetramer with total spin S = 1/2 formal oxidation states III, IV. The cuboidal arrangement of its oxygen atoms is similar to that proposed structures for the molecular cobaltate clusters cobalt-phosphate (Co-Pi) water-oxidizing catalyst. Davies electron-nuclear double resonance (ENDOR) spectrum well-modeled using...

We report the generation and characterization of a new high-spin iron(IV)–oxo complex supported by trigonal nonheme pyrrolide platform. Oxygen-atom transfer to [(tpaMes)FeII]− (tpaAr = tris(5-arylpyrrol-2-ylmethyl)amine) in acetonitrile solution affords Fe(III)–alkoxide product [(tpaMes2MesO)FeIII]− resulting from intramolecular C–H oxidation with no observable ferryl intermediates. In contrast, treatment phenyl derivative [(tpaPh)FeII]− trimethylamine N-oxide produces [(tpaPh)FeIV(O)]− that...

The radical S-adenosylmethionine (SAM) enzyme HydG lyses free l-tyrosine to produce CO and CN(-) for the assembly of catalytic H cluster FeFe hydrogenase. We used electron paramagnetic resonance spectroscopy detect characterize reaction intermediates generated with a set (2)H, (13)C, (15)N nuclear spin-labeled tyrosine substrates. propose detailed mechanism in which SAM reaction, initiated at an N-terminal 4Fe-4S cluster, generates bound C-terminal cluster. Heterolytic cleavage this Cα-Cβ...

Three iron-sulfur proteins--HydE, HydF, and HydG--play a key role in the synthesis of [2Fe](H) component catalytic H-cluster FeFe hydrogenase. The radical S-adenosyl-L-methionine enzyme HydG lyses free tyrosine to produce p-cresol CO CN(-) ligands cluster. Here, we applied stopped-flow Fourier transform infrared electron-nuclear double resonance spectroscopies probe formation HydG-bound Fe-containing species bearing with spectroscopic signatures that evolve on 1- 1000-second time scale....

Ribonucleotide reductases (RNRs) utilize radical chemistry to reduce nucleotides deoxynucleotides in all organisms. In the class Ia and Ib RNRs, this reaction requires a stable tyrosyl (Y(•)) generated by oxidation of reduced dinuclear metal cluster. The Fe(III)2-Y(•) cofactor NrdB subunit RNRs can be self-assembly from Fe(II)2-NrdB, O2, reducing equivalent. By contrast, structurally homologous enzymes require Mn(III)2-Y(•) their NrdF subunit. Mn(II)2-NrdF does not react with but it binds...

Co2+cobalmain (Co2+Cbl) is implicated in the catalytic cycles of all adenosylcobalamin (AdoCbl)-dependent enzymes, as each case catalysis initiated through homolytic cleavage cofactor's Co−C bond. The rate bond homolysis, while slow for free cofactor, accelerated by 12 orders magnitude when AdoCbl bound to protein active site, possibly enzyme-mediated stabilization post-homolysis products. As an essential step toward elucidation mechanism enzymatic activation, we employed electronic...

The monomeric iron(II) amido derivatives Fe{N(H)Ar*}2 (1), Ar* = C6H3-2,6-(C6H2-2,4,6-Pri 3)2, and Fe{N(H)Ar#}2 (2), Ar# C6H3-2,6-(C6H2-2,4,6-Me3)2, were synthesized studied in order to determine the effects of geometric changes on their unusual magnetic properties. compounds, which are first stable homoleptic primary amides iron(II), obtained by transamination Fe{N(SiMe3)2}2, with HN(SiMe3)2 elimination, amines H2NAr* or H2NAr#. X-ray crystallography showed that they have either strictly...

The bacterial manganese oxidase MnxG of the Mnx protein complex is unique among multicopper oxidases (MCOs) in carrying out a two-electron metal oxidation, converting Mn(II) to MnO2 nanoparticles. reaction occurs two stages: → Mn(III) and MnO2. In companion study, we show that electron transfer from low-potential type 1 Cu requires an activation step, likely forming hydroxide bridge at dinuclear site. Here study second oxidation using pyrophosphate (PP) as trap. PP chelates produced by...

Reductive dehalogenases play a critical role in the microbial detoxification of aquifers contaminated with chloroethenes and chlorethanes by catalyzing reductive elimination halogen. We report here first heterologous production vinyl chloride reductase VcrA from Dehalococcoides mccartyi strain VS. Heterologously expressed was reconstituted to its active form addition hydroxocobalamin/adenosylcobalamin, Fe3+, sulfide presence mercaptoethanol. The kinetic properties reduction Ti(III)-citrate...

High-resolution X-ray structures of photosystem II reveal several potential substrate binding sites at the water-oxidizing/oxygen-evolving 4MnCa cluster. Aspartate-61 D1 protein hydrogen bonds with one such water (W1), which is bound to dangler Mn4A oxygen-evolving complex. Comparison pulse EPR spectra (14)NH3 and (15)NH3 wild-type Synechocystis PSII a D1-D61A mutant lacking this hydrogen-bonding interaction demonstrates that ammonia binds as terminal NH3 site not partially deprotonated...

The antimicrobial protein calprotectin (CP), a hetero-oligomer of the S100 family members S100A8 and S100A9, is only identified mammalian Mn(II)-sequestering protein. Human CP uses Ca(II) ions to tune its Mn(II) affinity at biologically unprecedented hexahistidine site that forms S100A8/S100A9 interface, molecular basis for this phenomenon requires elucidation. Herein, we investigate remarkable coordination chemistry human using X-ray crystallography as well continuous-wave (CW) pulse...

The B(12) cofactors methylcobalamin (MeCbl) and 5'-deoxyadenosylcobalamin (AdoCbl) have long fascinated chemists because of their complex structures unusual reactivities in biological systems; however, electronic absorption (Abs) spectra remained largely unassigned. In this study, we used Abs, circular dichroism (CD), magnetic CD (MCD), resonance Raman spectroscopic techniques to probe the excited states Co(3+)Cbl species that differ with respect upper axial ligand, including MeCbl, AdoCbl,...

Multifrequency electron spin-echo envelope modulation (ESEEM) spectroscopy is used to ascertain the nature of bonding interactions various active site amino acids with Mn ions that compose oxygen-evolving cluster (OEC) in photosystem II (PSII) from cyanobacterium Synechocystis sp. PCC 6803 poised S(2) state. Spectra natural isotopic abundance PSII ((14)N-PSII), uniformly (15)N-labeled ((15)N-PSII), and (15)N-PSII containing (14)N-histidine ((14)N-His/(15)N-PSII) are compared. These...

S-Adenosyl methionine (SAM) is employed as a [4Fe-4S]-bound cofactor in the superfamily of radical SAM (rSAM) enzymes, which one-electron reduction [4Fe-4S]-SAM moiety leads to homolytic cleavage S-adenosyl generate 5'-deoxyadenosyl (5'dAdo•), potent H-atom abstractor. HydG, member this rSAM family, uses 5'dAdo• lyse its substrate, tyrosine, producing CO and CN that bind unique Fe site second HydG Fe-S cluster, ultimately mononuclear organometallic Fe-l-cysteine-(CO)2CN complex an...

The bacterial protein complex Mnx contains a multicopper oxidase (MCO) MnxG that, unusually, catalyzes the two-electron oxidation of Mn(II) to MnO2 biomineral, via Mn(III) intermediate. Although Mn(III)/Mn(II) and Mn(IV)/Mn(III) reduction potentials are expected be high, we find low potential, 0.38 V (vs Normal Hydrogen Electrode, pH 7.8), for type 1 Cu2+, electron acceptor. Indeed Cu2+ is not reduced by in absence molecular oxygen, indicating that substrate requires an activation step. We...

The human adenosyltransferase hATR converts exogenous cobalamin into coenzyme B12 by transferring the adenosyl group from cosubstrate ATP to a transiently formed Co1+cobalamin (Co1+Cbl) species. A particularly puzzling aspect of function is that midpoint potential for Co2+Cbl → Co1+Cbl reduction below readily available biological reductants. Our magnetic circular dichroism and electron paramagnetic resonance spectroscopic studies reported here reveal that, in absence ATP, interaction between...

CobA from Salmonella enterica is a member of an enzymatic system responsible for the de novo biosynthesis adenosylcobalamin (AdoCbl), catalyzing formation essential Co−C bond by transferring adenosyl group molecule ATP to transient Co1+corrinoid species generated in enzyme active site. A particularly fascinating aspect this reaction that flavodoxin vivo reducing agent serves as electron donor possesses reduction potential considerably more positive than Co2+/1+ couple corrinoid substrate. To...

The binding of the substrate analogue methanol to catalytic Mn4CaO5 cluster water-oxidizing enzyme photosystem II is known alter electronic structure properties oxygen-evolving complex without retarding O2-evolution under steady-state illumination conditions. We report mode (13)C-labeled determined using 9.4 GHz (X-band) hyperfine sublevel-correlation (HYSCORE) and 34 (Q-band) electron spin-echo nuclear double resonance (ESE-ENDOR) spectroscopies. These results are compared analogous...

Fluorinated tyrosines (FnY's, n = 2 and 3) have been site-specifically incorporated into E. coli class Ia ribonucleotide reductase (RNR) using the recently evolved M. jannaschii Y-tRNA synthetase/tRNA pair. Class RNRs require four redox active Y's, a stable Y radical (Y·) in β subunit (position 122 coli), three transiently oxidized Y's (356 731 730 α) to initiate radical-dependent nucleotide reduction process. FnY (3,5; 2,3; 2,3,5; 2,3,6) incorporation place of Y122-β X-ray structures each...

Abstract The synthesis of the first linear coordinated Cu II complex Cu{N(SiMe 3 )Dipp} 2 ( 1 Dipp=C 6 H 5 ‐2,6Pr i ) and its I counterpart [Cu{N(SiMe ] − is described. formation proceeds through a dispersion force‐driven disproportionation, reaction product halide LiN(SiMe )Dipp in non‐donor solvent. accomplished by preventing disproportionation into using complexing agent 15‐crown‐5. EPR spectroscopy provides detailed study two‐coordinate transition‐metal indicating strong covalency Cu−N bonds.

The wobble bases of tRNAs that decode split codons are often heavily modified. In bacteria, tRNA