Antiferromagnetic exchange interaction in the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima studied with a highly sensitive magnetic balance

The nature of chemical bonds in a ferredoxin-type [2Fe-2S] cluster hasbeen investigated on the basis of natural orbitals and several bond indices developed in Parts I and II of this study. The broken-symmetry hybrid density functional theory (BS-HDFT) with spin projection approach has been applied to elucidate the natural orbitals and occupation numbers for a model compound [Fe 2 S 2 (SCH 3 ) 4 ] (1), which is used to calculate the indices. The molecular structure, vibration frequencies, electronic structures, and magnetic properties in both oxidized and reduced forms of 1 have been calculated and compared with the experimental values. The optimized molecular structures after approximate spin projection have been in good agreement with experimental data. The structure changes upon one-electron reduction have been slight (Ͻ0.1 Å) and only limited around one side of the Fe atom. Raman and infrared (IR) spectra have been calculated, and their vibration modes have been assigned using the bridging 34 S isotope substitution. Their magnetic properties have been examined in terms of spin Hamiltonians that contain exchange interactions and double exchange interactions. The BS-HDFT methods have provided the magnetic parameters; i.e., effective exchange integral ( J) values and valence delocalization (B) values, which agree with the experimental results. It is found that large charge transfer (CT) from the bridging sulfur to the iron atoms has led to the strong antiferromagnetic interactions between iron atoms.

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“…Spinach J ox = −183 cm −1 28. Synechococcus lividus J ox = −185 cm −1 29, blue‐green alga Spirulina maxima J ox = −182 ± 20 cm −1 30.…”

Section: Resultsmentioning

confidence: 99%

“…Magnetic susceptibility measurements showed the antiferromagnetic coupling between two iron atoms 28–29. Characteristic EPR spectra with a lower g value were also observed 30.…”

Section: Introductionmentioning

confidence: 88%

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin‐type [2Fe–2S] cluster

Shoji

Koizumi

Taniguchi

et al. 2006

Int J of Quantum Chemistry

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“…There is a general tendency for the UHF methods underestimate the J values, while pure DFT methods overestimate J value 27, 28. The strong exchange interaction between Fe(III) spin sites are larger than experimentally determined J ≈ −180 cm −1 of [2Fe2S] ferredoxin 54–56. No experimental J value of Rieske protein in the oxidized state has been determined.…”

Section: Computational Results and Discussionmentioning

confidence: 99%

Theory of chemical bonds in metalloenzymes IV: Hybrid‐DFT study of Rieske‐type [2Fe2S] clusters

Shoji

Koizumi

Kitagawa

et al. 2006

Int J of Quantum Chemistry

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ABSTRACT:The Rieske-type [2FeO2S] cores of electron-transfer (ET) proteins in the mitochondrial respiratory chain have unusual properties, such as redox potentials and spectroscopy. In this study, part IV of a series, the inherent molecular structures and characteristic electronic structures of the Rieske-type [2FeO2S] clusters are investigated using broken-symmetry hybrid density functional theory (BS-HDFT). Geometry optimizations for the oxidized and reduced states were performed and their characteristic vibrational modes are assigned. Magnetic properties are investigated using model Hamiltonians to describe the electron delocalization and the unsymmetric property. The parameters of the model Hamiltonian, such as exchange coupling J, valence delocalization B, and potential energy difference ⌬, are evaluated from the BS-HDFT calculations. The valence localization and excitation energy (⌬E) of the Rieske-type [2FeO2S] cluster are discussed. The chemical bond nature is characterized by chemical indices from natural orbital analysis. Our theoretical results are reasonably consistent with experimental results.

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“…[34][35][36][37] Gaussian 09 softwarew as used to perform the calculations and thep rocedurer ecommended form odeling antiferromagnetic coupling [38] was followed to generate optimized HS and BS structures. [39] Calculations of the model oxidizedf erredoxins tructure in Ta ble 1s howt hat M06-L reproduces the experimentally obtained J value, [40] À182 AE 20 cm À1 , within experimental error and more accurately than the B3LYP functional. Therefore, the M06-L functional was also used for the calculation of the oxidized Rieske model.…”

mentioning

confidence: 94%

“…[29][30][31] The M06-L functional reproduces experiment bettert han calculationsu sing the B3LYP functional. [40] À182 AE 20…”

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confidence: 99%

Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron–Sulfur Cluster through ¹⁵N Vibrational Frequency Shifts

2015

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The Rieske [2Fe-2S] cluster is a vital component of many oxidoreductases, including mitochondrial cytochrome bc1; its chloroplast equivalent, cytochrome b6f; one class of dioxygenases; and arsenite oxidase. The Rieske cluster acts as an electron shuttle and its reduction is believed to couple with protonation of one of the cluster's His ligands. In cytochromes bc1 and b6f, for example, the Rieske cluster acts as the first electron acceptor in a modified Q cycle. The protonation states of the cluster's His ligands determine its ability to accept a proton and possibly an electron through a hydrogen bond to the electron carrier, ubiquinol. Experimental determination of the protonation states of a Rieske cluster's two His ligands by NMR spectroscopy is difficult, due to the close proximity of the two paramagnetic iron atoms of the cluster. Therefore, this work reports density functional calculations and proposes that difference vibrational spectroscopy with (15) N isotopic substitution may be used to assign the protonation states of the His ligands of the oxidized Rieske [2Fe-2S] complex.

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Antiferromagnetic exchange interaction in the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima studied with a highly sensitive magnetic balance

Cited by 47 publications

References 10 publications

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin‐type [2Fe–2S] cluster

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin‐type [2Fe–2S] cluster

Theory of chemical bonds in metalloenzymes IV: Hybrid‐DFT study of Rieske‐type [2Fe2S] clusters

Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron–Sulfur Cluster through ¹⁵N Vibrational Frequency Shifts

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Antiferromagnetic exchange interaction in the two-iron-two-sulphur ferredoxin from the blue-green alga Spirulina maxima studied with a highly sensitive magnetic balance

Cited by 47 publications

References 10 publications

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin‐type [2Fe–2S] cluster

Theory of chemical bonds in metalloenzymes III: Full geometry optimization and vibration analysis of ferredoxin‐type [2Fe–2S] cluster

Theory of chemical bonds in metalloenzymes IV: Hybrid‐DFT study of Rieske‐type [2Fe2S] clusters

Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron–Sulfur Cluster through 15N Vibrational Frequency Shifts

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Distinguishing Protonation States of Histidine Ligands to the Oxidized Rieske Iron–Sulfur Cluster through ¹⁵N Vibrational Frequency Shifts