An ultra-stable oxoiron(<scp>iv</scp>) complex and its blue conjugate base

England, Jason; Bigelow, Jennifer O.; Heuvelen, Katherine M. Van; Farquhar, Erik R.; Martinho, Marlène; Meier, Katlyn K.; Frisch, Jonathan R.; Münck, Eckard; Que, Lawrence

doi:10.1039/c3sc52755g

Cited by 61 publications

(76 citation statements)

References 45 publications

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“…The anionic, strongly donating thiolate ligand is able to stabilize the iron(IV) center upon oxo protonation to a greater extent than the analogous aqua ligand present in FeTMPS-II, 10 although a recent case involving an amidate oxyanion ligand apparently does not. 28 The relative importance of various parameters, such as the nature of the anionic ligand, Coulombic effects, σ- and π- trans -axial ligand effects, and field effects of other charges in the active sites of these proteins, has yet to be evaluated. The axial ligand is only one factor in determining the basicity of oxoFe IV porphyrins, however.…”

Section: Discussionmentioning

confidence: 99%

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Boaz

Bell

Groves³

2015

J. Am. Chem. Soc.

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Ferryl porphyrins, P−FeIV=O, are central reactive intermediates in the catalytic cycles of numerous heme proteins and a variety of model systems. There has been considerable interest in elucidating factors, such as terminal oxo basicity, that may control ferryl reactivity. Here, the sulfonated, water-soluble ferryl porphyrin complexes tetramesitylporphyrin, oxoFeIVTMPS (FeTMPS-II), its 2,6-dichlorophenyl analogue, oxoFeIVTDClPS (FeTDClPS-II), and two other analogues are shown to be protonated under turnover conditions to produce the corresponding bis-aqua-iron(III) porphyrin cation radicals. The results reveal a novel internal electromeric equilibrium, P−FeIV=O ⇆ P+−FeIII(OH2)2. Reversible pKa values in the range of 4–6.3 have been measured for this process by pH-jump, UV–vis spectroscopy. Ferryl protonation has important ramifications for C–H bond cleavage reactions mediated by oxoiron(IV) porphyrin cation radicals in protic media. Both solvent O–H and substrate C–H deuterium kinetic isotope effects are observed for these reactions, indicating that hydrocarbon oxidation by these oxoiron(IV) porphyrin cation radicals occurs via a solvent proton-coupled hydrogen atom transfer from the substrate that has not been previously described. The effective FeO–H bond dissociation energies for FeTMPS-II and FeTDClPS-II were estimated from similar kinetic reactivities of the corresponding oxoFeIVTMPS+ and oxoFeIVTDClPS+ species to be ~92–94 kcal/mol. Similar values were calculated from the two-proton P+−FeIII(OH2)2 pKaobs and the porphyrin oxidation potentials, despite a 230 mV range for the iron porphyrins examined. Thus, the iron porphyrin with the lower ring oxidation potential has a compensating higher basicity of the ferryl oxygen. The solvent-derived proton adds significantly to the driving force for C–H bond scission.

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Section: Discussionmentioning

confidence: 99%

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Boaz

Bell

Groves³

2015

J. Am. Chem. Soc.

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“…14,15, 16, 17,18,19 These enable an important step toward the elucidation of geometric and electronic properties contributing to NHFe function: the spectroscopic and quantum-chemical elucidation of the frontier molecular orbitals (FMOs) and their contributions to reactivity in model S = 1 and S = 2 Fe IV =O systems. 20,21,22,23,24,25,26,27,28 For the S = 1 Fe IV =O species, the pair of singly-occupied d π* FMOs, resulting from the strong antibonding interaction between oxo p x,y and Fe d xz/yz orbitals, were shown to define the π channel for H-atom abstraction (HAA) which requires for reactivity the perpendicular orientation of the substrate C—H bond with respect to the Fe—oxo bond.…”

Section: Introductionmentioning

confidence: 99%

Excited state potential energy surfaces and their interactions in Fe^IVO active sites

2014

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The non-heme ferryl active sites are of significant interest for their application in biomedical and green catalysis. These sites have been shown to have an S = 1 or S = 2 ground spin state; the latter is functional in biology. Low-temperature magnetic circular dichroism (LT MCD) spectroscopy probes the nature of the excited states in these species including ligand-field (LF) states that are otherwise difficult to study by other spectroscopies. In particular, the temperature dependences of MCD features enable their unambiguous assignment and thus determination of the low-lying excited states in two prototypical S = 1 and S = 2 NHFeIV=O complexes. Furthermore, some MCD bands exhibit vibronic structures that allow mapping of excited-state interactions and their effects on the potential energy surfaces (PESs). For the S = 2 species, there is also an unusual spectral feature in both near-infrared absorption and MCD spectra - Fano antiresonance (dip in Abs) and Fano resonance (sharp peak in MCD) that indicates the weak spin-orbit coupling of an S = 1 state with the S = 2 LF state. These experimental data are correlated with quantum-chemical calculations that are further extended to analyze the low-lying electronic states and the evolution of their multiconfigurational characters along the Fe—O PESs. These investigations show that the lowest-energy states develop oxyl FeIII character at distances that are relevant to the transition state (TS) for H-atom abstraction and define the frontier molecular orbitals that participate in the reactivity of S = 1 vs. S = 2 non-heme FeIV=O active sites. The S = 1 species has only one available channel that requires the C—H bond of a substrate to approach perpendicular to the Fe—oxo bond (the π channel). In contrast, there are three channels (one σ and two π) available for the S = 2 non-heme FeIV=O system allowing C—H substrate approach both along and perpendicular to the Fe—oxo bond that have important implications for enzymatic selectivity.

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“…In a recent study of an Figure 2) ligand with a pendant amide, formation of an unusual blue chromophore was observed upon deprotonation, which could be assigned using TDDFT to a ligand-tometal charge transfer transition from the enolate-like amide donor to a vacant (Fe d + O p)* orbital. [16] TDDFT was also found to be helpful for understanding the observed changes in Fe/α-ketoglutarate (α-KG) π* metal-to-ligand charge transfer upon variations of H-bonding, and 5/6-fold coordination, which reflect stabilization of the α-KG π* orbital directly influencing O2-reactivity in α-KG-dependent enzymes. [17] Figure 2.…”

Section: Density Functional Theory Calculations Of Spectroscopic Propmentioning

confidence: 99%

“…The correlation between OAT rates and reduction potentials (or quintet-triplet gap differences) was found in other studies as well. [16,206,207] The systematic work of Wilson et al [146] shed an additional light on OAT reactivity of NHFe IV =O complexes that was investigated (along with HAA reactivity) for two structurally related Figure 2). Unexpectedly, the rate was enhanced by two orders of magnitude for both HAA and OAT reactions of the TBC-supported complex (as compared to the complex with the TMC chelate).…”

Section: Mononuclear Ferryl Active Sitementioning

confidence: 99%

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

et al. 2016

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In this minireview, we provide an account of the current state-of-the-art developments in the area of mono-and binuclear non-heme enzymes (NHFe and NHFe2) and the smaller NHFe(2) synthetic models, mostly from a theoretical and computational perspective. The sheer complexity, and at the same time the beauty, of the NHFe(2) world represent a challenge for both experimental as well as theoretical methods. We emphasize that the concerted progress on both theoretical and experimental side is a conditio sine qua non for future understanding, exploration and utilization of the NHFe(2) systems.After briefly discussing the current challenges and advances in the computational methodology, we review the recent spectroscopic and computational studies of NHFe(2) enzymatic and inorganic systems and highlight the correlations between various experimental data (spectroscopic, kinetic, thermodynamic, electrochemical) and computations. Throughout, we attempt to keep in mind the most fascinating and attractive phenomenon in the NHFe(2) chemistry which is the fact that despite the strong oxidative power of many reactive intermediates, the NHFe(2) enzymes perform catalysis with high selectivity. We conclude with our personal viewpoint and hope that further developments in quantum chemistry and especially in the field of multireference wave function methods are needed to have a solid theoretical basis for the NHFe(2) studies, mostly by providing benchmarking and calibration of the computationally efficient and easy-to-use DFT methods.

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An ultra-stable oxoiron(iv) complex and its blue conjugate base

Cited by 61 publications

References 45 publications

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Excited state potential energy surfaces and their interactions in Fe^IVO active sites

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

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An ultra-stable oxoiron(iv) complex and its blue conjugate base

Cited by 61 publications

References 45 publications

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Ferryl Protonation in Oxoiron(IV) Porphyrins and Its Role in Oxygen Transfer

Excited state potential energy surfaces and their interactions in FeIVO active sites

Mono- and binuclear non-heme iron chemistry from a theoretical perspective

Contact Info

Product

Resources

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Excited state potential energy surfaces and their interactions in Fe^IVO active sites