Effects of Temperature and Pressure on the Mössbauer Spectra of Models for the [4Fe-4S]2+Clusters of Iron−Sulfur Proteins and the Structure of [PPh4]2[Fe4S4(SCH2CO2C2H5)4]

Silver, Jack; Fern, George R.; Miller, '; McCammon, C.; Evans, David; Leigh, G. J.

doi:10.1021/ic980157g

Cited by 19 publications

(17 citation statements)

References 33 publications

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“…The “harder” RO – form of HMBPP binds Fe1 more tightly than the ROH form, with concomitant lengthening of the Fe1–S 2– bonds. The net effect of these RO – geometries is an isomer shift for Fe1 that appears similar to what is observed in related [Fe 4 S 4 (SR) 4 ] 2– systems 66 , 107 , 108 and is more indicative of a valence delocalized Fe 2.5+ oxidation state. In contrast, when bound as an alcohol, the HMBPP–Fe1 distance is elongated with shortened Fe1–S 2– distances.…”

Section: Discussionsupporting

confidence: 59%

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Blachly

Sandala

Giammona

et al. 2014

J. Chem. Theory Comput.

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With current therapies becoming less efficacious due to increased drug resistance, new inhibitors of both bacterial and malarial targets are desperately needed. The recently discovered methylerythritol phosphate (MEP) pathway for isoprenoid synthesis provides novel targets for the development of such drugs. Particular attention has focused on the IspH protein, the final enzyme in the MEP pathway, which uses its [4Fe–4S] cluster to catalyze the formation of the isoprenoid precursors IPP and DMAPP from HMBPP. IspH catalysis is achieved via a 2e–/2H+ reductive dehydroxylation of HMBPP; the mechanism by which catalysis is achieved, however, is highly controversial. The work presented herein provides the first step in assessing different routes to catalysis by using computational methods. By performing broken-symmetry density functional theory (BS–DFT) calculations that employ both the conductor-like screening solvation model (DFT/COSMO) and a finite-difference Poisson–Boltzmann self-consistent reaction field methodology (DFT/SCRF), we evaluate geometries, energies, and Mössbauer signatures of the different protonation states that may exist in the oxidized state of the IspH catalytic cycle. From DFT/SCRF computations performed on the oxidized state, we find a state where the substrate, HMBPP, coordinates the apical iron in the [4Fe–4S] cluster as an alcohol group (ROH) to be one of two, isoenergetic, lowest-energy states. In this state, the HMBPP pyrophosphate moiety and an adjacent glutamate residue (E126) are both fully deprotonated, making the active site highly anionic. Our findings that this low-energy state also matches the experimental geometry of the active site and that its computed isomer shifts agree with experiment validate the use of the DFT/SCRF method to assess relative energies along the IspH reaction pathway. Additional studies of IspH catalytic intermediates are currently being pursued.

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Section: Discussionsupporting

confidence: 59%

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Blachly

Sandala

Giammona

et al. 2014

J. Chem. Theory Comput.

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“…was best simulated as two quadrupole doublets in a 3:1 ratio of roughly the same isomer shift (0.48 mm s -1 ), reflecting both i) the distinct coordination environment of the apical Fe center 70, 71 and ii) charge delocalization over the four Fe sites resulting in effective Fe oxidations state of +2.5. 1,[72][73][74][75] The structure of 12 shows the anticipated ligand binding mode with three Fe atoms bound by L(NIm Tol )3 and the unique Fe atom bound by Cl (Figure 3 In 12, the orientation of the imidazolyl groups positions one of the N-tolyl groups on each donor arm in a manner so as to confer substantial steric protection to the unique Fe site ( Figure 5). Moreover, the structure of 12 suggests further ways to tune the steric environment of the unique Fe site through simple modification of the imidazolyl ring substituents.…”

Section: Resultsmentioning

confidence: 99%

Selective Synthesis of Site-Differentiated Fe₄S₄ and Fe₆S₆ Clusters

McSkimming

Suess

2018

Inorg. Chem.

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Obtaining rational control over the structure and nuclearity of metalloclusters is an ongoing challenge in synthetic Fe-S cluster chemistry. We report a new family of tridentate imidazolin-2-imine ligands L(NIm R)3 that can bind [Fe4S4] 2+ or [Fe6S6] 3+ clusters, depending on the steric profile of the ligand and the reaction stoichiometry. A high-yielding synthetic route to L(NIm R)3 ligands (where R is the imidazolyl N substituents) from trianiline and 2-chloroimidazolium precursors is described. For L(NIm Me)3 (tris(1,3,5-(3-(N,N-dimethyl-4,5-diphenylimidazolin-2-imino)phenylmethyl))benzene), metalation with 1 equiv. [Ph4P]2[Fe4S4Cl4] and 3 equiv. NaBPh4 furnishes a mixture of products, but adjusting the stoichiometry to 1.5 equiv. [Ph4P]2[Fe4S4Cl4] provides (L(NIm Me)3)Fe6S6Cl6 in high yield. Formation of an [Fe6S6] 3+ cluster using L(NIm Tol)3 (tris(1,3,5-(3-(N,N-bis(4-methylphenyl)-4,5diphenylimidazolin-2-imino)phenylmethyl))benzene) is not observed; instead, the [Fe4S4] 2+ cluster [L(NIm Tol)3)(Fe4S4Cl)][BPh4] is cleanly generated when 1 equiv. [Ph4P]2[Fe4S4Cl4] is employed. The selectivity for cluster nuclearity is rationalized by the orientation of the imidazolyl rings whereby long N-imidazolyl substituents preclude formation of [Fe6S6] 3+ clusters but not [Fe4S4] 2+ clusters. Thus, the

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“…The irons in these binuclear complexes are linked by sulfide bridges, but in addition have different oxygen, nitrogen or sulfur ligands. The six 4Fe-4S complexes [Fe 4 S 4 (SPh) 4 ] 2− ,48,51 [Fe 4 S 4 (OPh) 4 ] 2− ,49 [Fe 4 S 4 (SPh) 2 Cl 2 ] 2− ,51 [Fe 4 S 4 (OPh) 2 Cl 2 ] 2− ,51 [Fe 4 S 4 Cl 4 ] 2− ,50,51 and [Fe 4 S 4 (SCH 2 CO 2 Et) 4 ] 2− 52 may be viewed as models of the 4Fe-4S cubane centers in ferredoxins and high-potential iron proteins (HiPIPs). Antiferromagnetic coupling between pairs of irons in these tetramers leads to overall diamagnetic compounds.…”

Section: Resultsmentioning

confidence: 99%

Density Functional Theory Calculations on Mössbauer Parameters of Nonheme Iron Nitrosyls

2009

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DFT calculations on transition metal nitrosyls often reveal unusual spin density profiles, involving substantial spatial separation of majority and minority spin densities. Against this context, there is a significant lack of studies where DFT calculations have been quantitatively calibrated against experimental spectroscopic properties. Reported herein are DFT calculations of Mössbauer isomer shifts and quadrupole splittings for 21 nonheme iron complexes (26 distinct iron sites) including 9 iron nitrosyls. Low-(S = 1/2) and high-spin (S = 3/2) {FeNO} 7 complexes, S = 1/2 {Fe(NO) 2 } 9 species, and polynuclear iron nitrosyls are all represented within the set of compounds examined. The general conclusion with respect to isomer shifts is that DFT (OLYP/STO-TZP) performs comparably well for iron nitrosyls and for iron complexes in general. However, quadrupole splittings are less accurately reproduced for nitrosyl complexes.

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Effects of Temperature and Pressure on the Mössbauer Spectra of Models for the [4Fe-4S]²⁺Clusters of Iron−Sulfur Proteins and the Structure of [PPh₄]₂[Fe₄S₄(SCH₂CO₂C₂H₅)₄]

Cited by 19 publications

References 33 publications

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Selective Synthesis of Site-Differentiated Fe₄S₄ and Fe₆S₆ Clusters

Density Functional Theory Calculations on Mössbauer Parameters of Nonheme Iron Nitrosyls

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Effects of Temperature and Pressure on the Mössbauer Spectra of Models for the [4Fe-4S]2+Clusters of Iron−Sulfur Proteins and the Structure of [PPh4]2[Fe4S4(SCH2CO2C2H5)4]

Cited by 19 publications

References 33 publications

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Use of Broken-Symmetry Density Functional Theory To Characterize the IspH Oxidized State: Implications for IspH Mechanism and Inhibition

Selective Synthesis of Site-Differentiated Fe4S4 and Fe6S6 Clusters

Density Functional Theory Calculations on Mössbauer Parameters of Nonheme Iron Nitrosyls

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Effects of Temperature and Pressure on the Mössbauer Spectra of Models for the [4Fe-4S]²⁺Clusters of Iron−Sulfur Proteins and the Structure of [PPh₄]₂[Fe₄S₄(SCH₂CO₂C₂H₅)₄]

Selective Synthesis of Site-Differentiated Fe₄S₄ and Fe₆S₆ Clusters