Ligand-Sensitive But Not Ligand-Diagnostic: Evaluating Cr Valence-to-Core X-ray Emission Spectroscopy as a Probe of Inner-Sphere Coordination

MacMillan, Samantha N.; Walroth, R. C.; Perry, Demetra M.; Morsing, Thorbjørn J.; Lancaster, Kyle M.

doi:10.1021/ic502152r

Cited by 37 publications

(56 citation statements)

References 53 publications

(88 reference statements)

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“…The picture becomes more complex in mixed coordination spheres, as both the nature of the ligand as well as variations in metal-ligand distance are known to influence the spectra. 31,39,46,51 Figure 3 (right) also shows the calculated VtC XES spectra, for the series of Cu proteins. The trends from the calculations generally agree well with experiment, with the exception of CusF (Met 2 His), where the intensity of the high energy VtC feature seems to be overestimated.…”

Section: Resultsmentioning

confidence: 99%

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

et al. 2016

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Biological systems use copper as a redox center in many metalloproteins, where the role of the metal is to cycle between its +1 and +2 oxidation states. This chemistry requires the redox potential to be in a range that can stabilize both Cu(I) and Cu(II) states, and often involves protein-derived ligand sets involving mixed histidine-methionine coordination that balance the preferences of both oxidation states. Transport proteins, on the other hand, utilize copper in the Cu(I) state, and often contain sites comprised predominately of the cuprophilic residue methionine. The electronic factors that allow enzymes and transporters to balance their redox requirements are complex, and are often elusive due to the dearth of spectroscopic probes of the Cu(I) state. Here we present the novel application of X-ray emission spectroscopy to copper proteins via a study of a series of mixed His - Met copper sites where the ligand set varies in a systematic way between the His3 and Met3 limits. The sites are derived from the wild-type peptidylglycine monooxygenase (PHM), two single-site variants which replicate each of its two copper sites (CuM-site and CuH-site), and the transporters CusF and CusB. Clear differences are observed in the Kβ2,5 region at the Met3 and His3 limits. CusB (Met3) has a distinct peak at 8978.4 eV with a broad shoulder at 8975.6 eV, whereas CuH (His3) has two well-resolved features: a more intense feature at 8974.8 eV and a second at 8977.2 eV. The mixed coordination sphere CusF (Met2His) and the PHM CuM variant (Met1His2) have very similar spectra consisting of two features at 8975.2 eV and 8977.8 eV Analysis of DFT calculated spectra indicate that the intensity of the higher energy peak near 8978 eV is mediated by mixing of ligand-based orbitals into the Cu d10 manifold, with S from Met providing more intensity by facilitating increased Cu p-d mixing. Furthermore, reaction of WT PHM with CO (an oxygen analogue) produced the M-site CO complex, which showed a unique XES spectrum that could be computationally reproduced by including interactions between Cu(I) and the CO ligand. The study suggests that the valence-to-core (VtC) region can serve as a probe of not only ligand speciation, but also offer insight into the coordination geometry, in a fashion similar to XAS pre-edges, and may be sufficiently sensitive to the coordination of exogenous ligands to be useful in the study of reaction mechanisms.

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Section: Resultsmentioning

confidence: 99%

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

et al. 2016

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“…Also shown are the values observed in experiment. 15,[64][65][66][67][68] This provides a measure of the capability of the calculations to predict the spectra with the correct absolute energy scale. The transition energies computed with the B3LYP functional are too low, and the extent that the experimental values are underestimated increases with the nuclear charge of the absorbing atom.…”

Section: Computational Detailsmentioning

confidence: 99%

Kohn-Sham density functional theory calculations of non-resonant and resonant x-ray emission spectroscopy

Hanson‐Heine

George

Besley

2017

The Journal of Chemical Physics

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The effect of basis set and exchange-correlation functional on time-dependent density functional theory calculations within the Tamm The accuracy of non-resonant and resonant (resonant inelastic X-ray scattering) X-ray emission spectra simulated based upon Kohn-Sham density functional theory is assessed. Accurate non-resonant X-ray emission spectra with the correct energy scale are obtained when short-range corrected exchangecorrelation functionals designed for the calculation of X-ray absorption spectroscopy are used. It is shown that this approach can be extended to simulate resonant inelastic X-ray scattering by using a reference determinant that describes a core-excited state. For this spectroscopy, it is found that a standard hybrid functional, B3LYP, gives accurate spectra that reproduce the features observed in experiment. However, the ability to correctly describe subtle changes in the spectra arising from different intermediate states is more challenging and requires averaging over conformations from a molecular dynamics simulation. Overall, it is demonstrated that accurate non-resonant and resonant X-ray emission spectra can be simulated directly from Kohn-Sham density functional theory.

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“…6, 7 K-edge (Metal 1s → valence/continuum) X-ray absorption spectroscopy (XAS) in particular has found widespread use in determining physical oxidation states of transition metal centres and qualitatively defining ligand geometries about these centres. 8-12 Weak “pre-edge” features in transition metal K-edge XAS are conventionally assigned as metal 1s → nd transitions.…”

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confidence: 99%

Probing Cu^I in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy

2015

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Ligand-Sensitive But Not Ligand-Diagnostic: Evaluating Cr Valence-to-Core X-ray Emission Spectroscopy as a Probe of Inner-Sphere Coordination

Cited by 37 publications

References 53 publications

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

Kohn-Sham density functional theory calculations of non-resonant and resonant x-ray emission spectroscopy

Probing Cu^I in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy

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Ligand-Sensitive But Not Ligand-Diagnostic: Evaluating Cr Valence-to-Core X-ray Emission Spectroscopy as a Probe of Inner-Sphere Coordination

Cited by 37 publications

References 53 publications

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

Kβ Valence to Core X-ray Emission Studies of Cu(I) Binding Proteins with Mixed Methionine – Histidine Coordination. Relevance to the Reactivity of the M- and H-sites of Peptidylglycine Monooxygenase

Kohn-Sham density functional theory calculations of non-resonant and resonant x-ray emission spectroscopy

Probing CuI in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy

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Probing Cu^I in homogeneous catalysis using high-energy-resolution fluorescence-detected X-ray absorption spectroscopy