Carboxylate shift mechanisms provide low-energy pathways to accommodate changes in oxidation state and coordination number required during catalysis metalloenzyme active sites. These processes are challenging observe their native enzymes molecular models can insight into mechanistic details. We report here the direct observation of a carboxylate reaction biomimetic yet structurally stable dicobalt complexes featuring both monodentate bridging acetate ligands, as well intramolecular...

Ribonucleotide reductase (RNR) catalyzes the conversion of nucleoside diphosphates to deoxynucleoside (dNDPs). The Escherichia coli class Ia RNR uses a mechanism radical propagation by which cysteine in active site large (α2) subunit is transiently oxidized stable tyrosyl (Y•) small (β2) over 35-Å pathway redox-active amino acids: Y122• ↔ [W48?] Y356 β2 Y731 Y730 C439 α2. When 3-aminotyrosine (NH2Y) incorporated place Y730, long-lived NH2Y730• generated α2 presence wild-type (wt)-β2,...

Artificial metalloproteins (ArMs) containing Co4O4 cubane active sites were constructed via biotin–streptavidin technology. Stabilized by hydrogen bonds (H-bonds), terminal and cofacial CoIII–OH2 moieties are observed crystallographically in a series of immobilized sites. Solution electrochemistry provided correlations oxidation potential pH. For variants Ser Phe adjacent to the metallocofactor, 1e–/1H+ chemistry predominates until pH 8, above which becomes pH-independent. Installation Tyr...

Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) Co

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides in all organisms. Active E. coli class Ia RNR is an α2β2 complex that undergoes reversible, long-range proton-coupled electron transfer (PCET) over a pathway redox active amino acids (β-Y122 → [β-W48] β-Y356 α-Y731 α-Y730 α-C439) spans ∼35 Å. To unmask PCET kinetics from rate-limiting conformational changes, we prepared photochemical containing [ReI] photooxidant site-specifically incorporated at...

The continued development of solar energy as a renewable resource necessitates new approaches to sustaining photodriven charge separation (CS). We present bioinspired approach in which photoinduced conformational rearrangements at ligand are translated into changes coordination geometry and environment about bound metal ion. Taking advantage the differential properties CuI CuII, these dynamics aim facilitate intramolecular electron transfer (ET) from create CS state. synthesis photophysical...

We report the electron transfer (ET) self-exchange rate constants (k11) for a pair of CuII/I complexes utilizing dpaR (dpa = dipicolylaniline, R OMe, SMe) ligands assessed by NMR line broadening experiments. These afford copper that are conformationally dynamic in one oxidation state. With CuI complex is dynamic, while with SMe, CuII dynamic. Both exhibit unexpectedly large k11 values 2.48(6) × 105 and 2.21(9) 106 M-1 s-1 [CuCl(dpaOMe)]+/0 [CuCl(dpaSMe)]+/0, respectively. Among fastest...

The geometries of copper coordination complexes are intricately related to their electron transfer capabilities, but the role dynamics in these processes not fully understood. We have previously reported CuCl(dpaOMe), a complex exhibiting conformational fluxionality its CuI state and rigidity upon oxidation CuII. Here, we report synthesis characterization [CuCl(dpaSMe)]+/0, relative structural [CuCl(dpaSMe)]+ were characterized via X-ray diffraction, cyclic voltammetry, EPR spectroscopy,...

Ribonucleotide reductase (RNR) catalyzes the conversion of ribonucleotides to deoxyribonucleotides provide monomeric building blocks for DNA replication and repair. Nucleotide reduction occurs by way multistep proton-coupled electron transfer (PCET) over a pathway redox active amino acids spanning ∼35 Å two subunits (α2 β2). Despite fact that PCET in RNR is rapid, slow conformational changes mask examination kinetics these steps. As such, we have pioneered methodology which site-specific...

Spectroscopic and electrochemical investigations into the conformational dynamics of Cu complexes bearing flexible functionalized dipicolylamine (dpa) ligands.

The Escherichia coli class Ia ribonucleotide reductase (RNR) achieves forward and reverse proton-coupled electron transfer (PCET) over a pathway of redox active amino acids (β-Y122 ⇌ β-Y356 α-Y731 α-Y730 α-C439) spanning ∼35 Å two subunits every time it turns over. We have developed photoRNRs that allow radical transport to be phototriggered at tyrosine (Y) or fluorotyrosine (FnY) residues along the PCET pathway. now report new photoRNR in which photooxidation tryptophan (W) residue...

Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides (NDP) to deoxynucleotides (dNDP), in part, by controlling ratios and quantities dNTPs available for DNA replication repair. The active form Escherichia coli class Ia RNR is an asymmetric α2β2 complex which α2 contains site β2 stable diferric-tyrosyl radical cofactor responsible initiating reduction chemistry. Each dNDP accompanied disulfide bond formation. We now report that, under vitro conditions, can initiate turnover...

The conversion of solar energy into chemical fuel represents a capstone goal the 21st century and has potential to supply terawatts power in globally distributed manner. However, disparate time scales photodriven charge separation (∼fs) steps reactions (∼μs) represent an inherent bottleneck solar-to-fuels technology. To address this discrepancy, we are developing earth-abundant coordination complexes that undergo light-induced conformational rearrangements such (CS) is hastened, while...

Substrate turnover in class Ia ribonucleotide reductase (RNR) requires reversible radical transport across two subunits over 35 Å, which occurs by a multistep proton-coupled electron-transfer mechanism. Using photooxidant-labeled β2 subunit of Escherichia coli RNR, we demonstrate photoinitiated oxidation tyrosine an α2:β2 complex, results substrate turnover. site-directed mutations the redox-active tyrosines at interface, Y356F(β) and Y731F(α), this is identified to be localized on Y356. The...

From the reduction of dinitrogen to oxidation water, chemical transformations catalyzed by metalloenzymes underlie global geo- and biochemical cycles. These reactions represent some most kinetically thermodynamically challenging processes known. They require complex choreography nature’s fundamental building blocks: electrons protons, be carried out with utmost precision accuracy; mistimed synchronicity can fatal. Gated macrostructural conformational changes, rate-determining steps catalysis...

From the reduction of dinitrogen to oxidation water, chemical transformations catalyzed by metalloenzymes underlie global geo- and biochemical cycles. These reactions represent some most kinetically thermodynamically challenging processes known. They require complex choreography nature’s fundamental building blocks: electrons protons, be carried out with utmost precision accuracy; mistimed synchronicity can fatal. Gated macrostructural conformational changes, rate-determining steps catalysis...

The 2011 discovery of the first rare earth-dependent enzyme in methylotrophic

Many naturally occurring metalloenzymes are gated by rate-limiting conformational changes, and there exists a critical interplay between macroscopic structural rearrangements of the protein subatomic changes affecting electronic structure embedded metallocofactors. Despite this connection, most artificial metalloproteins (ArMs) prepared in structurally rigid hosts. To better model natural mechanisms metalloprotein reactivity, we have developed conformationally switchable ArMs (swArMs) that...

Abstract Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) Co III (cat 2− ) and high (h.s.) II (sq⋅ − forms =catecholato, sq⋅ =seminquinonato of 3,5−di− t Bu‐1,2‐dioxolene), which reversibly interconvert via temperature‐dependent intramolecular electron transfer. Typically, the remaining four coordination sites on are supported by a tetradentate ligand whose properties influence temperature at VT occurs. We report that replacing one...

Active site hydrogen-bond (H-bond) networks represent a key component by which metalloenzymes control the formation and deployment of high-valent transition metal-oxo intermediates. We report series dinuclear cobalt complexes that serve as structural models for nonheme diiron enzyme family feature Co2(μ-OH)2 diamond core stabilized intramolecular H-bond interactions. define conditions required kinetically controlled synthesis these complexes: [Co2(μ-OH)2(μ-OAc)(κ1-OAc)2(pyR)4][PF6] (1R),...