NMR Analysis of Spin Densities

Bren, Kara L.

doi:10.1002/9781118898277.ch16

Cited by 8 publications

(7 citation statements)

References 101 publications

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“…The preferred delocalization of the electron spin along the Fe 2+ site ligands correlates well with ET directionality of these proteins; redox chemistry is exclusively catalyzed at the reducible Fe 2+ /Fe 3+ site of the cluster, maximizing the electronic coupling with redox partners. ,,,,− The amino-acid-selective isotopic labeling strategy and 2D spectroscopy allow separation and assignments of the resonances from Cys- 13 C β located at the second coordination sphere of different irons, not possible from uniform 13 C labeling and 1D experiments . In spite of the wide application of NMR to quantify electron spin distributions in paramagnetic systems, , Cys- 13 C β nuclei around the paramagnetic Fe–S cluster are located too close to the irons and are often not observed experimentally. , The methodology used in this work opens the way for direct determination of the isotropic and anisotropic couplings for 13 C β -Cys in paramagnetic clusters complementary to the paramagnetic NMR approach. In conjunction with DFT computations it is expected to be applicable for rapid and robust characterizations of the spin density distribution onto the ligands of other clusters and metallocomplexes, critical to a quantum mechanical understanding of the chemistry.…”

Section: Discussionmentioning

confidence: 99%

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

et al. 2017

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Iron-sulfur clusters are one of the most versatile and ancient classes of redox mediators in biology. The roles that these metal centers take on are predominantly determined by the number and types of coordinating ligands (typically cysteine and histidine) that modify the electronic structure of the cluster. Here we map the spin density distribution onto the cysteine ligands for the three major classes of the protein-bound, reduced [2Fe-2S](His)(Cys) (n = 0, 1, 2) cluster by selective cysteine-C isotope labeling. The spin distribution is highly asymmetric in all three systems and delocalizes further along the reduced Fe ligands than the nonreducible Fe ligands for all clusters studied. The preferential spin transfer onto the chemically reactive Fe ligands is consistent with the structural concept that the orientation of the cluster in proteins is not arbitrarily decided, but rather is optimized such that it is likely to facilitate better electronic coupling with redox partners. The resolution of all cysteine-C hyperfine couplings and their assignments provides a measure of the relative covalencies of the metal-thiolate bonds not readily available to other techniques.

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Section: Discussionmentioning

confidence: 99%

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

et al. 2017

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“…Ni bidentate phosphine complexes can be characterized by NMR spectroscopy because many are diamagnetic, giving well-resolved spectra that are free of paramagnetic shifts and associated line broadening . Ciofini and coworkers noted in a recent study, however, that predicting and rationalizing 31 P chemical shifts of metal complexes is complicated by the contrasting effects of ligand donation and back-bonding .…”

Section: Introductionmentioning

confidence: 99%

“…Ni bidentate phosphine complexes can be characterized by NMR spectroscopy because many are diamagnetic, 44 giving well-resolved spectra that are free of paramagnetic shifts and associated line broadening. 45 Ciofini and coworkers noted in a recent study, however, that predicting and rationalizing 31 P chemical shifts of metal complexes is complicated by the contrasting effects of ligand donation and back-bonding. 46 This challenge in rationalizing 31 P chemical shifts makes analyzing organometallic reaction mixtures less straightforward in comparison to using 1 H and 13 C chemical shifts for organic molecules.…”

Section: ■ Introductionmentioning

confidence: 99%

Using J_PP to Identify Ni Bidentate Phosphine Complexes In Situ

2021

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Identifying intermediates of Ni-containing reactions can be challenging due to the high reactivity of Ni complexes and their sensitivity toward air and moisture. Many Ni bidentate phosphine complexes are diamagnetic and can be analyzed in situ via 31P NMR spectroscopy, but the oxidation state of Ni is difficult to determine using 31P chemical shift analysis alone. The J-coupling between P atoms, J PP, has been proposed to correlate with oxidation state, but few investigations have looked at how J PP is affected by parameters such as length of the linker or identity of the phosphine or other ligands. The present investigation into the J PP values of Ni bidentate phosphine complexes with two-carbon and three-carbon linkers shows that the J PP values observed in 31P NMR spectra, |J PP|, are competent indicators of the oxidation state at Ni. For complexes with two-carbon linkers, |J PP| > 40 Hz is typical of Ni0 while |J PP| < 30 Hz is typical of NiII; this trend is reversed for complexes with three-carbon linkers. Additionally, the Lewis acidity of the Ni and Lewis basicity of the phosphine ligand affect J PP predictably. For example, increased P-to-Ni donation arising from more-donating phosphines or more-withdrawing ligands trans to the P atoms causes a more negative J PP. These results should enable the oxidation state of Ni and properties of ligands in Ni bidentate phosphine complexes to be determined in situ during reactions containing these species.

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“…Paramagnetic proteins are also amenable to study by NMR, although the information gained is different from diamagnetic NMR (Bren, 2015). The large magnetic moment of an unpaired electron will alter the chemical shift of nuclei during the NMR experiment, a difference referred to as isotropic shift, through two mechanisms known as contact shift and pseudocontact shift.…”

Section: Nuclear Magnetic Resonancementioning

confidence: 99%

Overview of Methods for Purification and Characterization of Metalloproteins

2021

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Metalloproteins make up one third of all proteins and perform some of the most essential reactions on earth. The unique properties of the metal ions within these proteins, and in particular of redox‐active metal ions, enables the use of a number of characterization techniques. It also necessitates unique considerations in terms of purification and characterization. In this overview, we describe the considerations and methods used for metalloprotein purification and characterization. © 2021 Wiley Periodicals LLC.

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NMR Analysis of Spin Densities

Cited by 8 publications

References 101 publications

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

Using J_PP to Identify Ni Bidentate Phosphine Complexes In Situ

Overview of Methods for Purification and Characterization of Metalloproteins

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NMR Analysis of Spin Densities

Cited by 8 publications

References 101 publications

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by 13Cβ-Cysteine Labeling

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by 13Cβ-Cysteine Labeling

Using JPP to Identify Ni Bidentate Phosphine Complexes In Situ

Overview of Methods for Purification and Characterization of Metalloproteins

Contact Info

Product

Resources

About

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

Unpaired Electron Spin Density Distribution across Reduced [2Fe-2S] Cluster Ligands by ¹³C_β-Cysteine Labeling

Using J_PP to Identify Ni Bidentate Phosphine Complexes In Situ