Synthetic analogs of the active sites of iron-sulfur proteins. V. Proton resonance properties of the tetranuclear clusters [tetra-.mu.-sulfido-tetrakis(alkyl or aryl thiolato)tetraferrate](2-)

Holm, R. H.; Phillips, William D.; Averill, Bruce A.; Mayerle, J. J.; Herskovitz, T.

doi:10.1021/ja00814a020

Cited by 113 publications

(71 citation statements)

References 4 publications

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“…This observation parallels the results obtained by Holm and co-workers, who also observed opposite-sign contact shifts for the para hydrogen atom in [Fe 4 [18]. Meanwhile, the magnitudes of the a proton contact shifts follow a similar trend as that observed for the H2 protons.…”

Section: H Nmr Analysissupporting

confidence: 91%

“…The fact that both the NH and H2 protons are shifted to lower frequencies by contact interactions indicates the presence of same-sign spin densities at positions 1 and 2 of the indole-3-thiolate ligand. An analogous spin distribution has been found in the indole radical cation, [19] in contrast to thiophenolate-based systems, in which neighboring hydrogen atoms generally display opposite-sign contact shifts [18].…”

Section: H Nmr Analysissupporting

confidence: 61%

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N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

Geer

Koten

et al. 2008

Inorganica Chimica Acta

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A series of N-substituted indole-3-thiols, synthesized by sequential alkylation, thiouronium salt formation, and hydrolysis, are used to generate a novel family of [4Fe-4S] clusters. The redox transitions of the clusters deviate from those of other [4Fe-4S] cluster families, with half-wave potentials lying in a range midway between those of [4Fe-4S] clusters bound by aliphatic thiolate ligands and those bound by thiophenolate-based ligands. In UV-vis spectroscopy, the new cluster family shows absorption maxima that are among the most redshifted reported thus far in [4Fe-4S] cluster chemistry. The indole-3-thiolate ligand thus leads to a highly specific and uncommon combination of [4Fe-4S] cluster properties, which can be fine-tuned by facile derivatization at the indole nitrogen atom.

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Section: H Nmr Analysissupporting

confidence: 91%

Section: H Nmr Analysissupporting

confidence: 61%

N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

Geer

Koten

et al. 2008

Inorganica Chimica Acta

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“…The a-CH protons also are subject to a similar perturbation with an attenuation factor, as compared to p-CH2 protons, of about 7.2. This factor was established from PMR studies of the synthetic dianion analogs (15,16 Fig. 3 (intensity corresponding to two protons) was in fact not observed in our 220 MHz PMR studies (Fig.…”

Section: Resultsmentioning

confidence: 61%

Proton Magnetic Resonance and Magnetic Susceptibility Characterization of Ferredoxin I from Bacillus polymyxa

Phillips

McDonald

Stombaugh

et al. 1974

Proc. Natl. Acad. Sci. U.S.A.

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Magnetic susceptibility and proton magnetic resonance spectra are reported for the oxidized and reduced forms of the iron-sulfur protein Bacillus polymyxa ferredoxin I. The magnetic susceptibility of the oxidized form indicates antiferromagnetic exchange coupling between component iron atoms that is quantitatively similar to that observed for the clostridial ferredoxins and for the [(C2Hs)4N2[Fe4S4(SCH2C6H5)41 analog. Contact-shifted resonances observed in the proton-magnetic-resonance spectra of oxidized and reduced forms of the B. polymyxa protein can-be correlated with the contact-shifted resonances of corresponding redox forms of the clostridial ferredoxins. Characteristics of the contact-shifted resonances observed in partially reduced B. polynmyxa ferredoxin I are compatible with a "slow" rate of electron exchange between redox forms, which suggests that the "fast" electron exchange earlier observed in the eight-iron clostridial ferredoxins may derive from an intramolecular component.In recent years, a new subdivision of bacterial ferredoxins containing only a single cluster of four iron and four labile sulfur atoms per molecule has become known; two members of this new subclass of bacterial ferredoxins have been isolated(1) from the facultative nitrogen fixing bacterium Bacilus polymyxa and their chemical, physical, and electron paramagnetic resonance (EPR) properties defined (1-4). Both of these proteins have molecular weights of about 9000 daltons and contain four iron atoms and four labile sulfur atoms per molecule. Both optical absorption and EPR spectra strongly suggest that the iron and labile sulfur atoms in the four-iron ferredoxin are arranged into a single tetrameric cluster similar to the two tetrameric clusters found in the more complex eightiron bacterial ferredoxins (5). The purpose of this study was to investigate the magnetic susceptibility and proton magnetic resonance (PMR) properties of one of these four-iron ferredoxins, B. polymyxa ferredoxin I, in order to further characterize this new type of iron-sulfur protein. It same basic geometrical type, a hypothesis that must necessarily be tested by crystallographic means and which emphasizes the role of the protein moiety in dictating the electron-transfer properties (potentials and specificities) of these proteins. MATERIALS AND METHODSThe B. polymyxa ferredoxin I employed in these studies was isolated and purified by methods previously described (1). Reductions were carried out using British Drug House Na2S204. Nuclear magnetic resonance (NMR) spectra for the most part were obtained on a Varian 220 MHz PMR spectrometer; searches to extreme low-field were carried out on a Bruker 90 MHz spectrometer. Magnetic susceptibilities were determined by previously described NMR techniques (6).

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“…All protons resonate at chemical shifts significantly different from those of the corresponding protons in the free ligand N 2 2ThE , which is consistent with the presence of three unpaired electrons in the cobalt complex. Unambiguous signal assignment has been achieved on the basis of the isotropic shifts, essentially attributable to a Fermi contact contribution [70][71][72]. …”

Section: Co II Complexesmentioning

confidence: 99%

Olefin oligomerization, homopolymerization and copolymerization by late transition metals supported by (imino)pyridine ligands

Bianchini

Giambastiani

Luconi

et al. 2010

Coordination Chemistry Reviews

294

147

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Synthetic analogs of the active sites of iron-sulfur proteins. V. Proton resonance properties of the tetranuclear clusters [tetra-.mu.-sulfido-tetrakis(alkyl or aryl thiolato)tetraferrate](2-)

Cited by 113 publications

References 4 publications

N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

N-Substituted indole-3-thiolate [4Fe–4S] clusters with a unique and tunable combination of spectral and redox properties

Proton Magnetic Resonance and Magnetic Susceptibility Characterization of Ferredoxin I from Bacillus polymyxa

Olefin oligomerization, homopolymerization and copolymerization by late transition metals supported by (imino)pyridine ligands

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