1
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Fritsch L, Rehsies P, Barakat W, Estes DP, Bauer M. Detection and Characterization of Hydride Ligands in Copper Complexes by Hard X-Ray Spectroscopy. Chemistry 2024; 30:e202400357. [PMID: 38651986 DOI: 10.1002/chem.202400357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2024] [Revised: 04/17/2024] [Accepted: 04/18/2024] [Indexed: 04/25/2024]
Abstract
Transition metal complexes, particularly copper hydrides, play an important role in various catalytic processes and molecular inorganic chemistry. This study employs synchrotron hard X-ray spectroscopy to gain insights into the geometric and electronic properties of copper hydrides as potential catalysts for CO2 hydrogenation. The potential of high energy resolution X-ray absorption near-edge structure (HERFD-XANES) and valence-to-core X-ray emission (VtC-XES) is demonstrated with measurement on Stryker's reagent (Cu6H6) and [Cu3(μ3-H)(dpmppe)2](PF6)2 (Cu3H), alongside a non-hydride copper compound ICu(dtbppOH) (Cuy-I). The XANES analysis reveals that coordination geometries strongly influence the spectra, providing only indirect details about hydride coordination. The VtC-XES analysis exhibits a distinct signal around 8975 eV, offering a diagnostic tool to identify hydride ligands. Theoretical calculations support and extend these findings by comparing hydride-containing complexes with their hydride-free counterparts.
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Affiliation(s)
- Lorena Fritsch
- Institute of Inorganic Chemistry and Center for Sustainable Systems Design (CSSD), Paderborn University, Warburger Straße 100, 33098, Paderborn, Germany
| | - Pia Rehsies
- Institute of Inorganic Chemistry and Center for Sustainable Systems Design (CSSD), Paderborn University, Warburger Straße 100, 33098, Paderborn, Germany
| | - Wael Barakat
- Instritute of Technical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Deven P Estes
- Instritute of Technical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569, Stuttgart, Germany
| | - Matthias Bauer
- Institute of Inorganic Chemistry and Center for Sustainable Systems Design (CSSD), Paderborn University, Warburger Straße 100, 33098, Paderborn, Germany
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2
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Geoghegan BL, Bilyj JK, Bernhardt PV, DeBeer S, Cutsail GE. X-ray absorption and emission spectroscopy of N 2S 2 Cu(II)/(III) complexes. Dalton Trans 2024; 53:7828-7838. [PMID: 38624161 DOI: 10.1039/d4dt00085d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2024]
Abstract
This study investigates the influence of ligand charge on transition energies in a series of CuN2S2 complexes based on dithiocarbazate Schiff base ligands using Cu K-edge X-ray absorption spectroscopy (XAS) and Kβ valence-to-core (VtC) X-ray emission spectroscopy (XES). By comparing the formally Cu(II) complexes [CuII(HL1)] (HL12- = dimethyl pentane-2,4-diylidenebis[carbonodithiohydrazonate]) and [CuII(HL2)] (HL22- = dibenzyl pentane-2,4-diylidenebis[carbonodithiohydrazonate]) and the formally Cu(III) complex [CuIII(L2)], distinct changes in transition energies are observed, primarily attributed to the metal oxidation state. Density functional theory (DFT) calculations demonstrate how an increased negative charge on the deprotonated L23- ligand stabilizes the Cu(III) center through enhanced charge donation, modulating the core transition energies. Overall, significant shifts to higher energies are noted upon metal oxidation, emphasizing the importance of scrutinizing ligand structure in XAS/VtC XES analysis. The data further support the redox-innocent role of the Schiff base ligands and underscore the criticality of ligand protonation levels in future spectroscopic studies, particularly for catalytic intermediates. The combined XAS-VtC XES methodology validates the Cu(III) oxidation state assignment while offering insights into ligand protonation effects on core-level spectroscopic transitions.
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Affiliation(s)
- Blaise L Geoghegan
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstrasse 5-7, 45117 Essen, Germany
- Department of Chemistry, Imperial College London, Molecular Sciences Research Hub, W12 0BZ, London, UK
| | - Jessica K Bilyj
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
| | - Paul V Bernhardt
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane 4072, Australia
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
| | - George E Cutsail
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany.
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstrasse 5-7, 45117 Essen, Germany
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3
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Wollweber T, Ayyer K. Nanoscale x-ray imaging with high spectral sensitivity using fluorescence intensity correlations. STRUCTURAL DYNAMICS (MELVILLE, N.Y.) 2024; 11:024307. [PMID: 38638700 PMCID: PMC11026111 DOI: 10.1063/4.0000245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/12/2024] [Accepted: 03/18/2024] [Indexed: 04/20/2024]
Abstract
This paper introduces spectral incoherent diffractive imaging (SIDI) as a novel method for achieving dark-field imaging of nanostructures with heterogeneous oxidation states. With SIDI, shifts in photoemission profiles can be spatially resolved, enabling the independent imaging of the underlying emitter distributions contributing to each spectral line. In the x-ray domain, this approach offers unique insights beyond the conventional combination of diffraction and x-ray emission spectroscopy. When applied at x-ray free-electron lasers, SIDI promises to be a versatile tool for investigating a broad range of systems, offering unprecedented opportunities for detailed characterization of heterogeneous nanostructures for catalysis and energy storage, including of their ultrafast dynamics.
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Affiliation(s)
| | - Kartik Ayyer
- Author to whom correspondence should be addressed:
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4
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Rush KW, Eastman KAS, Welch EF, Bandarian V, Blackburn NJ. Capturing the Binuclear Copper State of Peptidylglycine Monooxygenase Using a Peptidyl-Homocysteine Lure. J Am Chem Soc 2024; 146:5074-5080. [PMID: 38363651 PMCID: PMC11096088 DOI: 10.1021/jacs.3c14705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/18/2024]
Abstract
Peptidylglycine monooxygenase is a copper-dependent enzyme that catalyzes C-alpha hydroxylation of glycine extended pro-peptides, a critical post-translational step in peptide hormone processing. The canonical mechanism posits that dioxygen binds at the mononuclear M-center to generate a Cu(II)-superoxo species capable of H atom abstraction from the peptidyl substrate, followed by long-range electron tunneling from the CuH center. Recent crystallographic and biochemical data have challenged this mechanism, suggesting instead that an "open-to-closed" transition brings the copper centers closer, allowing reactivity within a binuclear intermediate. Here we present the first direct observation of an enzyme-bound binuclear copper species, captured by the use of an Ala-Ala-Phe-hCys inhibitor complex. This molecule reacts with the fully reduced enzyme to form a thiolate-bridged binuclear species characterized by EXAFS of the WT and its M314H variant and with the oxidized enzyme to form a novel mixed valence entity characterized by UV/vis and EPR. Mechanistic implications are discussed.
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Affiliation(s)
- Katherine W. Rush
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR 97239, USA
| | | | - Evan F. Welch
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR 97239, USA
| | - Vahe Bandarian
- Department of Chemistry, University of Utah, Salt Lake City, UT 84112, USA
| | - Ninian J. Blackburn
- Department of Chemical Physiology and Biochemistry, Oregon Health & Science University, Portland, OR 97239, USA
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5
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Lim H, Brueggemeyer MT, Transue WJ, Meier KK, Jones SM, Kroll T, Sokaras D, Kelemen B, Hedman B, Hodgson KO, Solomon EI. Kβ X-ray Emission Spectroscopy of Cu(I)-Lytic Polysaccharide Monooxygenase: Direct Observation of the Frontier Molecular Orbital for H 2O 2 Activation. J Am Chem Soc 2023; 145:16015-16025. [PMID: 37441786 PMCID: PMC10557184 DOI: 10.1021/jacs.3c04048] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/15/2023]
Abstract
Lytic polysaccharide monooxygenases (LPMOs) catalyze the degradation of recalcitrant carbohydrate polysaccharide substrates. These enzymes are characterized by a mononuclear Cu(I) active site with a three-coordinate T-shaped "His-brace" configuration including the N-terminal histidine and its amine group as ligands. This study explicitly investigates the electronic structure of the d10 Cu(I) active site in a LPMO using Kβ X-ray emission spectroscopy (XES). The lack of inversion symmetry in the His-brace site enables the 3d/p mixing required for intensity in the Kβ valence-to-core (VtC) XES spectrum of Cu(I)-LPMO. These Kβ XES data are correlated to density functional theory (DFT) calculations to define the bonding, and in particular, the frontier molecular orbital (FMO) of the Cu(I) site. These experimentally validated DFT calculations are used to evaluate the reaction coordinate for homolytic cleavage of the H2O2 O-O bond and understand the contribution of this FMO to the low barrier of this reaction and how the geometric and electronic structure of the Cu(I)-LPMO site is activated for rapid reactivity with H2O2.
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Affiliation(s)
- Hyeongtaek Lim
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | | | - Wesley J Transue
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Katlyn K Meier
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Stephen M Jones
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Thomas Kroll
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Bradley Kelemen
- IFF Health and Biosciences, Palo Alto, California 94304, United States
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Keith O Hodgson
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Edward I Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
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6
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Arias RJ, Welch EF, Blackburn NJ. New structures reveal flexible dynamics between the subdomains of peptidylglycine monooxygenase. Implications for an open to closed mechanism. Protein Sci 2023; 32:e4615. [PMID: 36880254 PMCID: PMC10031757 DOI: 10.1002/pro.4615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Revised: 02/28/2023] [Accepted: 03/02/2023] [Indexed: 03/08/2023]
Abstract
Peptidylglycine monooxygenase (PHM) is essential for the biosynthesis of many neuroendocrine peptides via a copper-dependent hydroxylation of a glycine-extended pro-peptide. The "canonical" mechanism requires the transfer of two electrons from one mononuclear copper (CuH, H-site) to a second mononuclear copper (CuM, M-site) which is the site of oxygen binding and catalysis. In most crystal structures the copper centers are separated by 11 Å of disordered solvent, but recent work has established that a PHM variant H108A forms a closed conformer in the presence of citrate with a reduced Cu-Cu site separation of ~4 Å. Here we report three new PHM structures where the H and M sites are separated by a longer distance of ~14 Å. Variation in Cu-Cu distance is the result of a rotation of the M subdomain about a hinge point centered on the pro199 -leu200 -ile201 triad which forms the linker between subdomains. The energetic cost of domain dynamics is likely small enough to allow free rotation of the subdomains relative to each other, adding credence to recent suggestions that an open-to-closed transition to form a binuclear oxygen binding intermediate is an essential element of catalysis. This inference would explain many experimental observations that are inconsistent with the current canonical mechanism including substrate-induced oxygen activation and isotope scrambling during the peroxide shunt.
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Affiliation(s)
- Renee J. Arias
- Department of Chemical Physiology and BiochemistryOregon Health and Science UniversityPortlandOregonUSA
- Present address:
Materials and Structural Analysis Division, Thermo Fisher ScientificHillsboroOregonUSA
| | - Evan F. Welch
- Department of Chemical Physiology and BiochemistryOregon Health and Science UniversityPortlandOregonUSA
- Department of Biomedical EngineeringOregon Health and Science UniversityPortlandOregonUSA
| | - Ninian J. Blackburn
- Department of Chemical Physiology and BiochemistryOregon Health and Science UniversityPortlandOregonUSA
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7
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Reznik N, Gallo AD, Rush KW, Javitt G, Fridmann-Sirkis Y, Ilani T, Nairner NA, Fishilevich S, Gokhman D, Chacón KN, Franz KJ, Fass D. Intestinal mucin is a chaperone of multivalent copper. Cell 2022; 185:4206-4215.e11. [PMID: 36206754 DOI: 10.1016/j.cell.2022.09.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Revised: 06/21/2022] [Accepted: 09/09/2022] [Indexed: 01/26/2023]
Abstract
Mucus protects the epithelial cells of the digestive and respiratory tracts from pathogens and other hazards. Progress in determining the molecular mechanisms of mucus barrier function has been limited by the lack of high-resolution structural information on mucins, the giant, secreted, gel-forming glycoproteins that are the major constituents of mucus. Here, we report how mucin structures we determined enabled the discovery of an unanticipated protective role of mucus: managing the toxic transition metal copper. Using two juxtaposed copper binding sites, one for Cu2+ and the other for Cu1+, the intestinal mucin, MUC2, prevents copper toxicity by blocking futile redox cycling and the squandering of dietary antioxidants, while nevertheless permitting uptake of this important trace metal into cells. These findings emphasize the value of molecular structure in advancing mucosal biology, while introducing mucins, produced in massive quantities to guard extensive mucosal surfaces, as extracellular copper chaperones.
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Affiliation(s)
- Nava Reznik
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Annastassia D Gallo
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Katherine W Rush
- Department of Chemistry, Reed College, Portland, Oregon 97202, United States; Oregon Health & Science University, Portland, Oregon 97239, United States
| | - Gabriel Javitt
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Yael Fridmann-Sirkis
- Life Sciences Core Facilities, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Tal Ilani
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Noa A Nairner
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Simon Fishilevich
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - David Gokhman
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Kelly N Chacón
- Department of Chemistry, Reed College, Portland, Oregon 97202, United States
| | - Katherine J Franz
- Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
| | - Deborah Fass
- Department of Chemical and Structural Biology, Weizmann Institute of Science, Rehovot 7610001, Israel.
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8
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Welch EF, Rush KW, Arias RJ, Blackburn NJ. Pre-Steady-State Reactivity of Peptidylglycine Monooxygenase Implicates Ascorbate in Substrate Triggering of the Active Conformer. Biochemistry 2022; 61:665-677. [PMID: 35380039 PMCID: PMC9064607 DOI: 10.1021/acs.biochem.2c00080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Peptidylglycine monooxygenase (PHM) is essential for the posttranslational amidation of neuroendocrine peptides. An important aspect of the PHM mechanism is the complete coupling of oxygen reduction to substrate hydroxylation, which implies no oxygen reactivity of the fully reduced enzyme in the absence of peptidyl substrates. As part of studies aimed at investigating this feature of the PHM mechanism, we explored pre-steady-state kinetics using chemical quench (CQ) and rapid freeze-quench (RFQ) studies of the fully reduced ascorbate-free PHM enzyme. First, we confirmed the absence of Cu(I)-enzyme oxidation by O2 at catalytic rates in the absence of peptidyl substrate. Next, we investigated reactivity in the presence of the substrate dansyl-YVG. Surprisingly, when ascorbate-free di-Cu(I) PHM was shot against oxygenated buffer containing the dansyl-YVG substrate, <15% of the expected product was formed. Substoichiometric reactivity was confirmed by stopped-flow and RFQ EPR spectroscopy. Product generation reached a maximum of 70% by the addition of increasing amounts of the ascorbate cosubstrate in a process that was not the result of multiple turnovers. FTIR spectroscopy of the Cu(I)-CO reaction chemistry was then used to show that increasing ascorbate concentrations correlated with a substrate-induced Cu(I)M-CO species characteristic of an altered conformation. We conclude that ascorbate and peptidyl substrate work together to induce a transition from an inactive to an active conformation and suggest that the latter may represent the "closed" conformation (Cu-Cu of ∼4 Å) recently observed for both PHM and its sister enzyme DBM by crystallography.
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Affiliation(s)
- Evan F Welch
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.,Department of Biomedical Engineering, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
| | - Katherine W Rush
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States.,Department of Chemistry, Reed College, 3203 SE Woodstock Blvd, Portland, Oregon 97202, United States
| | - Renee J Arias
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
| | - Ninian J Blackburn
- Department of Chemical Physiology and Biochemistry, Oregon Health and Science University, 3181 SW Sam Jackson Park Road, Portland, Oregon 97239, United States
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9
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Geoghegan BL, Liu Y, Peredkov S, Dechert S, Meyer F, DeBeer S, Cutsail GE. Combining Valence-to-Core X-ray Emission and Cu K-edge X-ray Absorption Spectroscopies to Experimentally Assess Oxidation State in Organometallic Cu(I)/(II)/(III) Complexes. J Am Chem Soc 2022; 144:2520-2534. [PMID: 35050605 PMCID: PMC8855422 DOI: 10.1021/jacs.1c09505] [Citation(s) in RCA: 25] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
A series of organometallic
copper complexes in formal oxidation
states ranging from +1 to +3 have been characterized by a combination
of Cu K-edge X-ray absorption (XAS) and Cu Kβ valence-to-core
X-ray emission spectroscopies (VtC XES). Each formal oxidation state
exhibits distinctly different XAS and VtC XES transition energies
due to the differences in the Cu Zeff, concomitant with
changes in physical oxidation state from +1 to +2 to +3. Herein, we
demonstrate the sensitivity of XAS and VtC XES to the physical oxidation
states of a series of N-heterocyclic carbene (NHC) ligated organocopper
complexes. We then extend these methods to the study of the [Cu(CF3)4]− ion. Complemented by computational
methods, the observed spectral transitions are correlated with the
electronic structure of the complexes and the Cu Zeff.
These calculations demonstrate that a contraction of the Cu 1s orbitals
to deeper binding energy upon oxidation of the Cu center manifests
spectroscopically as a stepped increase in the energy of both XAS
and Kβ2,5 emission features with increasing formal
oxidation state within the [Cun+(NHC2)]n+ series. The newly synthesized Cu(III) cation
[CuIII(NHC4)]3+ exhibits spectroscopic
features and an electronic structure remarkably similar to [Cu(CF3)4]−, supporting a physical oxidation
state assignment of low-spin d8 Cu(III) for [Cu(CF3)4]−. Combining XAS and VtC XES
further demonstrates the necessity of combining multiple spectroscopies
when investigating the electronic structures of highly covalent copper
complexes, providing a template for future investigations into both
synthetic and biological metal centers.
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Affiliation(s)
- Blaise L. Geoghegan
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstrasse 5-7, 45117 Essen, Germany
| | - Yang Liu
- Institute of Inorganic Chemistry, University of Göttingen, Tammannstrasse 4, 37077 Göttingen, Germany
| | - Sergey Peredkov
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - Sebastian Dechert
- Institute of Inorganic Chemistry, University of Göttingen, Tammannstrasse 4, 37077 Göttingen, Germany
| | - Franc Meyer
- Institute of Inorganic Chemistry, University of Göttingen, Tammannstrasse 4, 37077 Göttingen, Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
| | - George E. Cutsail
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, 45470 Mülheim an der Ruhr, Germany
- Institute of Inorganic Chemistry, University of Duisburg-Essen, Universitätsstrasse 5-7, 45117 Essen, Germany
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10
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Gerz I, Jannuzzi SAV, Hylland KT, Negri C, Wragg DS, Øien‐Ødegaard S, Tilset M, Olsbye U, DeBeer S, Amedjkouh M. Structural Elucidation, Aggregation, and Dynamic Behaviour of
N,N,N,N
‐Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X‐ray Spectroscopic and Crystallographic Investigation. Eur J Inorg Chem 2021; 2021:4762-4775. [PMID: 35874966 PMCID: PMC9298233 DOI: 10.1002/ejic.202100722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Revised: 09/22/2021] [Indexed: 12/30/2022]
Abstract
A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1‐H‐imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X‐ray spectroscopic techniques. The differences between the imidazole‐ and pyridine‐based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu−Nimine bond lengths from single‐crystal X‐ray diffraction measurements. Variable‐temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature‐dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K‐edge XAS and VtC XES, where DFT‐assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal‐organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.
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Affiliation(s)
- Isabelle Gerz
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | | | - Knut T. Hylland
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - Chiara Negri
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - David S. Wragg
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - Sigurd Øien‐Ødegaard
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - Mats Tilset
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - Unni Olsbye
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
| | - Serena DeBeer
- Department of Inorganic Spectroscopy Max Planck Institute for Chemical Energy Conversion Stiftstraße 34–36 45470 Mülheim an der Ruhr Germany
| | - Mohamed Amedjkouh
- Department of Chemistry University of Oslo P. O. Box 1033 Blindern 0315 Oslo Norway
- Centre for Materials Science and Nanotechnology University of Oslo P.O. Box 1126 Blindern 0316 Oslo Norway
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11
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Mathe Z, McCubbin Stepanic O, Peredkov S, DeBeer S. Phosphorus Kβ X-ray emission spectroscopy detects non-covalent interactions of phosphate biomolecules in situ. Chem Sci 2021; 12:7888-7901. [PMID: 34168842 PMCID: PMC8188515 DOI: 10.1039/d1sc01266e] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Phosphorus is ubiquitous in biochemistry, being found in the phosphate groups of nucleic acids and the energy-transferring system of adenine nucleotides (e.g. ATP). Kβ X-ray emission spectroscopy (XES) of phosphorus has been largely unexplored, with no previous applications to biomolecules. Here, the potential of P Kβ XES to study phosphate-containing biomolecules, including ATP and NADPH, is evaluated, as is the application of the technique to aqueous solution samples. P Kβ spectra offer a detailed picture of phosphate valence electronic structure, reporting on subtle non-covalent effects, such as hydrogen bonding and ionic interactions, that are key to enzymatic catalysis. Spectral features are interpreted using density functional theory (DFT) calculations, and potential applications to the study of biological energy conversion are highlighted. Phosphorus X-ray emission spectroscopy probes non-covalent interactions and electronic structure of phosphate biomolecules in both solid and solution samples.![]()
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Affiliation(s)
- Zachary Mathe
- Max Planck Institute for Chemical Energy Conversion Stiftstr. 34-36 D-45470 Mülheim an der Ruhr Germany
| | - Olivia McCubbin Stepanic
- Max Planck Institute for Chemical Energy Conversion Stiftstr. 34-36 D-45470 Mülheim an der Ruhr Germany
| | - Sergey Peredkov
- Max Planck Institute for Chemical Energy Conversion Stiftstr. 34-36 D-45470 Mülheim an der Ruhr Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion Stiftstr. 34-36 D-45470 Mülheim an der Ruhr Germany
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12
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Biasin E, Nascimento DR, Poulter BI, Abraham B, Kunnus K, Garcia-Esparza AT, Nowak SH, Kroll T, Schoenlein RW, Alonso-Mori R, Khalil M, Govind N, Sokaras D. Revealing the bonding of solvated Ru complexes with valence-to-core resonant inelastic X-ray scattering. Chem Sci 2021; 12:3713-3725. [PMID: 34163645 PMCID: PMC8179428 DOI: 10.1039/d0sc06227h] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 01/21/2021] [Indexed: 12/27/2022] Open
Abstract
Ru-complexes are widely studied because of their use in biological applications and photoconversion technologies. We reveal novel insights into the chemical bonding of a series of Ru(ii)- and Ru(iii)-complexes by leveraging recent advances in high-energy-resolution tender X-ray spectroscopy and theoretical calculations. We perform Ru 2p4d resonant inelastic X-ray scattering (RIXS) to probe the valence excitations in dilute solvated Ru-complexes. Combining these experiments with a newly developed theoretical approach based on time-dependent density functional theory, we assign the spectral features and quantify the metal-ligand bonding interactions. The valence-to-core RIXS features uniquely identify the metal-centered and charge transfer states and allow extracting the ligand-field splitting for all the complexes. The combined experimental and theoretical approach described here is shown to reliably characterize the ground and excited valence states of Ru complexes, and serve as a basis for future investigations of ruthenium, or other 4d metals active sites, in biological and chemical applications.
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Affiliation(s)
- Elisa Biasin
- Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
| | - Daniel R Nascimento
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory Richland Washington 99352 USA
| | - Benjamin I Poulter
- Department of Chemistry, University of Washington Seattle Washington 98195 USA
| | - Baxter Abraham
- SSRL, SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Kristjan Kunnus
- Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
- LCLS, SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
| | | | - Stanislaw H Nowak
- SSRL, SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Thomas Kroll
- SSRL, SLAC National Accelerator Laboratory Menlo Park California 94025 USA
| | - Robert W Schoenlein
- Stanford PULSE Institute, SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
- LCLS, SLAC National Accelerator Laboratory Menlo Park CA 94025 USA
| | | | - Munira Khalil
- Department of Chemistry, University of Washington Seattle Washington 98195 USA
| | - Niranjan Govind
- Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory Richland Washington 99352 USA
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13
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Phu PN, Gutierrez CE, Kundu S, Sokaras D, Kroll T, Warren TH, Stieber SCE. Quantification of Ni-N-O Bond Angles and NO Activation by X-ray Emission Spectroscopy. Inorg Chem 2021; 60:736-744. [PMID: 33373520 DOI: 10.1021/acs.inorgchem.0c02724] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A series of β-diketiminate Ni-NO complexes with a range of NO binding modes and oxidation states were studied by X-ray emission spectroscopy (XES). The results demonstrate that XES can directly probe and distinguish end-on vs side-on NO coordination modes as well as one-electron NO reduction. Density functional theory (DFT) calculations show that the transition from the NO 2s2s σ* orbital has higher intensity for end-on NO coordination than for side-on NO coordination, whereas the 2s2s σ orbital has lower intensity. XES calculations in which the Ni-N-O bond angle was fixed over the range from 80° to 176° suggest that differences in NO coordination angles of ∼10° could be experimentally distinguished. Calculations of Cu nitrite reductase (NiR) demonstrate the utility of XES for characterizing NO intermediates in metalloenzymes. This work shows the capability of XES to distinguish NO coordination modes and oxidation states at Ni and highlights applications in quantifying small molecule activation in enzymes.
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Affiliation(s)
- Phan N Phu
- Department of Chemistry & Biochemistry, California State Polytechnic University, Pomona, California 91768, United States
| | - Carlos E Gutierrez
- Department of Chemistry & Biochemistry, California State Polytechnic University, Pomona, California 91768, United States
| | - Subrata Kundu
- Department of Chemistry, Georgetown University, Box 571227, Washington, D.C. 20057, United States.,School of Chemistry, Indian Institute of Science Education and Research Thiruvananthapuram, Kerala 695551, India
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Thomas Kroll
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Timothy H Warren
- Department of Chemistry, Georgetown University, Box 571227, Washington, D.C. 20057, United States
| | - S Chantal E Stieber
- Department of Chemistry & Biochemistry, California State Polytechnic University, Pomona, California 91768, United States
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14
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Lim H, Baker ML, Cowley RE, Kim S, Bhadra M, Siegler MA, Kroll T, Sokaras D, Weng TC, Biswas DR, Dooley DM, Karlin KD, Hedman B, Hodgson KO, Solomon EI. Kβ X-ray Emission Spectroscopy as a Probe of Cu(I) Sites: Application to the Cu(I) Site in Preprocessed Galactose Oxidase. Inorg Chem 2020; 59:16567-16581. [PMID: 33136386 DOI: 10.1021/acs.inorgchem.0c02495] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Cu(I) active sites in metalloproteins are involved in O2 activation, but their O2 reactivity is difficult to study due to the Cu(I) d10 closed shell which precludes the use of conventional spectroscopic methods. Kβ X-ray emission spectroscopy (XES) is a promising technique for investigating Cu(I) sites as it detects photons emitted by electronic transitions from occupied orbitals. Here, we demonstrate the utility of Kβ XES in probing Cu(I) sites in model complexes and a metalloprotein. Using Cu(I)Cl, emission features from double-ionization (DI) states are identified using varying incident X-ray photon energies, and a reasonable method to correct the data to remove DI contributions is presented. Kβ XES spectra of Cu(I) model complexes, having biologically relevant N/S ligands and different coordination numbers, are compared and analyzed, with the aid of density functional theory (DFT) calculations, to evaluate the sensitivity of the spectral features to the ligand environment. While the low-energy Kβ2,5 emission feature reflects the ionization energy of ligand np valence orbitals, the high-energy Kβ2,5 emission feature corresponds to transitions from molecular orbitals (MOs) having mainly Cu 3d character with the intensities determined by ligand-mediated d-p mixing. A Kβ XES spectrum of the Cu(I) site in preprocessed galactose oxidase (GOpre) supports the 1Tyr/2His structural model that was determined by our previous X-ray absorption spectroscopy and DFT study. The high-energy Kβ2,5 emission feature in the Cu(I)-GOpre data has information about the MO containing mostly Cu 3dx2-y2 character that is the frontier molecular orbital (FMO) for O2 activation, which shows the potential of Kβ XES in probing the Cu(I) FMO associated with small-molecule activation in metalloproteins.
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Affiliation(s)
- Hyeongtaek Lim
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Michael L Baker
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Ryan E Cowley
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Sunghee Kim
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Mayukh Bhadra
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Maxime A Siegler
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Thomas Kroll
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Dimosthenis Sokaras
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Tsu-Chien Weng
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Dalia R Biswas
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States
| | - David M Dooley
- Department of Chemistry and Biochemistry, Montana State University, Bozeman, Montana 59717, United States.,University of Rhode Island, Kingston, Rhode Island 02881, United States
| | - Kenneth D Karlin
- Department of Chemistry, Johns Hopkins University, Baltimore, Maryland 21218, United States
| | - Britt Hedman
- Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Keith O Hodgson
- Department of Chemistry, Stanford University, Stanford, California 94305, United States.,Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
| | - Edward I Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, United States.,Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, California 94025, United States
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15
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McCubbin Stepanic O, Ward J, Penner-Hahn JE, Deb A, Bergmann U, DeBeer S. Probing a Silent Metal: A Combined X-ray Absorption and Emission Spectroscopic Study of Biologically Relevant Zinc Complexes. Inorg Chem 2020; 59:13551-13560. [PMID: 32893611 PMCID: PMC7509839 DOI: 10.1021/acs.inorgchem.0c01931] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
As the second most common transition metal in the human body, zinc is of great interest to research but has few viable routes for its direct structural study in biological systems. Herein, Zn valence-to-core X-ray emission spectroscopy (VtC XES) and Zn K-edge X-ray absorption spectroscopy (XAS) are presented as a means to understand the local structure of zinc in biological systems through the application of these methods to a series of biologically relevant molecular model complexes. Taken together, the Zn K-edge XAS and VtC XES provide a means to establish the ligand identity, local geometry, and metal-ligand bond lengths. Experimental results are supported by correlation with density-functional-theory-based calculations. Combining these theoretical and experimental approaches will enable future applications to protein systems in a predictive manner.
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Affiliation(s)
- Olivia McCubbin Stepanic
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Jesse Ward
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - James E Penner-Hahn
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Aniruddha Deb
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
| | - Uwe Bergmann
- Stanford PULSE Institute, SLAC National Accelerator Laboratory, Menlo Park, California 94025, United States
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion, Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany
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16
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Castillo RG, Henthorn JT, McGale J, Maganas D, DeBeer S. Kβ X-Ray Emission Spectroscopic Study of a Second-Row Transition Metal (Mo) and Its Application to Nitrogenase-Related Model Complexes. Angew Chem Int Ed Engl 2020; 59:12965-12975. [PMID: 32363668 PMCID: PMC7496169 DOI: 10.1002/anie.202003621] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Indexed: 01/03/2023]
Abstract
In recent years, X-ray emission spectroscopy (XES) in the Kβ (3p-1s) and valence-to-core (valence-1s) regions has been increasingly used to study metal active sites in (bio)inorganic chemistry and catalysis, providing information about the metal spin state, oxidation state and the identity of coordinated ligands. However, to date this technique has been limited almost exclusively to first-row transition metals. In this work, we present an extension of Kβ XES (in both the 4p-1s and valence-to-1s [or VtC] regions) to the second transition row by performing a detailed experimental and theoretical analysis of the molybdenum emission lines. It is demonstrated in this work that Kβ2 lines are dominated by spin state effects, while VtC XES of a 4d transition metal provides access to metal oxidation state and ligand identity. An extension of Mo Kβ XES to nitrogenase-relevant model complexes shows that the method is sufficiently sensitive to act as a spectator probe for redox events that are localized at the Fe atoms. Mo VtC XES thus has promise for future applications to nitrogenase, as well as a range of other Mo-containing biological cofactors. Further, the clear assignment of the origins of Mo VtC XES features opens up the possibility of applying this method to a wide range of second-row transition metals, thus providing chemists with a site-specific tool for the elucidation of 4d transition metal electronic structure.
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Affiliation(s)
- Rebeca G. Castillo
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an der RuhrGermany
| | - Justin T. Henthorn
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an der RuhrGermany
| | - Jeremy McGale
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an der RuhrGermany
| | - Dimitrios Maganas
- Max-Planck-Institut für KohlenforschungKaiser-Wilhelm-Platz 145470Mülheim an der RuhrGermany
| | - Serena DeBeer
- Department of Inorganic SpectroscopyMax Planck Institute for Chemical Energy ConversionStiftstrasse 34–3645470Mülheim an der RuhrGermany
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17
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Castillo RG, Henthorn JT, McGale J, Maganas D, DeBeer S. Kβ X‐Ray Emission Spectroscopic Study of a Second‐Row Transition Metal (Mo) and Its Application to Nitrogenase‐Related Model Complexes. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202003621] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Rebeca G. Castillo
- Department of Inorganic Spectroscopy Max Planck Institute for Chemical Energy Conversion Stiftstrasse 34–36 45470 Mülheim an der Ruhr Germany
| | - Justin T. Henthorn
- Department of Inorganic Spectroscopy Max Planck Institute for Chemical Energy Conversion Stiftstrasse 34–36 45470 Mülheim an der Ruhr Germany
| | - Jeremy McGale
- Department of Inorganic Spectroscopy Max Planck Institute for Chemical Energy Conversion Stiftstrasse 34–36 45470 Mülheim an der Ruhr Germany
| | - Dimitrios Maganas
- Max-Planck-Institut für Kohlenforschung Kaiser-Wilhelm-Platz 1 45470 Mülheim an der Ruhr Germany
| | - Serena DeBeer
- Department of Inorganic Spectroscopy Max Planck Institute for Chemical Energy Conversion Stiftstrasse 34–36 45470 Mülheim an der Ruhr Germany
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18
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Holden WM, Jahrman EP, Govind N, Seidler GT. Probing Sulfur Chemical and Electronic Structure with Experimental Observation and Quantitative Theoretical Prediction of Kα and Valence-to-Core Kβ X-ray Emission Spectroscopy. J Phys Chem A 2020; 124:5415-5434. [PMID: 32486638 DOI: 10.1021/acs.jpca.0c04195] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
An extensive experimental and theoretical study of the Kα and Kβ high-resolution X-ray emission spectroscopy (XES) of sulfur-bearing systems is presented. This study encompasses a wide range of organic and inorganic compounds, including numerous experimental spectra from both prior published work and new measurements. Employing a linear-response time-dependent density functional theory (LR-TDDFT) approach, strong quantitative agreement is found in the calculation of energy shifts of the core-to-core Kα as well as the full range of spectral features in the valence-to-core Kβ spectrum. The ability to accurately calculate the sulfur Kα energy shift supports the use of sulfur Kα XES as a bulk-sensitive tool for assessing sulfur speciation. The fine structure of the sulfur Kβ spectrum, in conjunction with the theoretical results, is shown to be sensitive to the local electronic structure including effects of symmetry, ligand type and number, and, in the case of organosulfur compounds, to the nature of the bonded organic moiety. This agreement between theory and experiment, augmented by the potential for high-access XES measurements with the latest generation of laboratory-based spectrometers, demonstrates the possibility of broad analytical use of XES for sulfur and nearby third-row elements. The effective solution of the forward problem, i.e., successful prediction of detailed spectra from known molecular structure, also suggests future use of supervised machine learning approaches to experimental inference, as has seen recent interest for interpretation of X-ray absorption near-edge structure (XANES).
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Affiliation(s)
- William M Holden
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Evan P Jahrman
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
| | - Niranjan Govind
- Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, P.O. Box 999, Richland, Washington 99352, United States
| | - Gerald T Seidler
- Department of Physics, University of Washington, Seattle, Washington 98195, United States
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19
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Nowak SH, Armenta R, Schwartz CP, Gallo A, Abraham B, Garcia-Esparza AT, Biasin E, Prado A, Maciel A, Zhang D, Day D, Christensen S, Kroll T, Alonso-Mori R, Nordlund D, Weng TC, Sokaras D. A versatile Johansson-type tender x-ray emission spectrometer. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2020; 91:033101. [PMID: 32259983 DOI: 10.1063/1.5121853] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2019] [Accepted: 02/13/2020] [Indexed: 05/23/2023]
Abstract
We present a high energy resolution x-ray spectrometer for the tender x-ray regime (1.6-5.0 keV) that was designed and operated at Stanford Synchrotron Radiation Lightsource. The instrument is developed on a Rowland geometry (500 mm of radius) using cylindrically bent Johansson analyzers and a position sensitive detector. By placing the sample inside the Rowland circle, the spectrometer operates in an energy-dispersive mode with a subnatural line-width energy resolution (∼0.32 eV at 2400 eV), even when an extended incident x-ray beam is used across a wide range of diffraction angles (∼30° to 65°). The spectrometer is enclosed in a vacuum chamber, and a sample chamber with independent ambient conditions is introduced to enable a versatile and fast-access sample environment (e.g., solid/gas/liquid samples, in situ cells, and radioactive materials). The design, capabilities, and performance are presented and discussed.
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Affiliation(s)
- S H Nowak
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - R Armenta
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - C P Schwartz
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - A Gallo
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - B Abraham
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - A T Garcia-Esparza
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - E Biasin
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - A Prado
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - A Maciel
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - D Zhang
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - D Day
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - S Christensen
- National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, Colorado 80401, USA
| | - T Kroll
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - R Alonso-Mori
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - D Nordlund
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - T-C Weng
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
| | - D Sokaras
- SLAC National Accelerator Laboratory, 2575 Sand Hill Rd., Menlo Park, California 94025, USA
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20
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Mathe Z, Pantazis DA, Lee HB, Gnewkow R, Van Kuiken BE, Agapie T, DeBeer S. Calcium Valence-to-Core X-ray Emission Spectroscopy: A Sensitive Probe of Oxo Protonation in Structural Models of the Oxygen-Evolving Complex. Inorg Chem 2019; 58:16292-16301. [PMID: 31743026 PMCID: PMC6891804 DOI: 10.1021/acs.inorgchem.9b02866] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Indexed: 12/12/2022]
Abstract
Calcium is an abundant, nontoxic metal that finds many roles in synthetic and biological systems including the oxygen-evolving complex (OEC) of photosystem II. Characterization methods for calcium centers, however, are underdeveloped compared to those available for transition metals. Valence-to-core X-ray emission spectroscopy (VtC XES) selectively probes the electronic structure of an element's chemical environment, providing insight that complements the geometric information available from other techniques. Here, the utility of calcium VtC XES is established using an in-house dispersive spectrometer in combination with density functional theory. Spectral trends are rationalized within a molecular orbital framework, and Kβ2,5 transitions, derived from molecular orbitals with primarily ligand p character, are found to be a promising probe of the calcium coordination environment. In particular, it is shown that calcium VtC XES is sensitive to the electronic structure changes that accompany oxo protonation in Mn3CaO4-based molecular mimics of the OEC. Through correlation to calculations, the potential of calcium VtC XES to address unresolved questions regarding the mechanism of biological water oxidation is highlighted.
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Affiliation(s)
- Zachary Mathe
- Max Planck Institute
for Chemical Energy Conversion, Stiftstrasse 34−36, D-45470 Mülheim an der Ruhr, Germany
| | - Dimitrios A. Pantazis
- Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mülheim an der
Ruhr, Germany
| | - Heui Beom Lee
- Division of Chemistry and
Chemical Engineering, California Institute
of Technology, Pasadena, California 91125, United States
| | - Richard Gnewkow
- Institute of Optics and Atomic Physics, Technical University of Berlin, Hardenbergstraße 36, D-10587 Berlin, Germany
| | - Benjamin E. Van Kuiken
- Max Planck Institute
for Chemical Energy Conversion, Stiftstrasse 34−36, D-45470 Mülheim an der Ruhr, Germany
| | - Theodor Agapie
- Division of Chemistry and
Chemical Engineering, California Institute
of Technology, Pasadena, California 91125, United States
| | - Serena DeBeer
- Max Planck Institute
for Chemical Energy Conversion, Stiftstrasse 34−36, D-45470 Mülheim an der Ruhr, Germany
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21
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Burkhardt L, Mueller C, Groß OA, Sun Y, Sitzmann H, Bauer M. The Bonding Situation in the Dinuclear Tetra-Hydrido Complex [{ 5CpFe} 2(μ-H) 4] Revisited by Hard X-Ray Spectroscopy. Inorg Chem 2019; 58:6609-6618. [PMID: 30596494 DOI: 10.1021/acs.inorgchem.8b03032] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
High energy resolution fluorescence detected XANES (HERFD-XANES) and valence-to-core X-ray emission spectroscopy (VtC-XES) are introduced as powerful tools to investigate hydride-iron interaction, the possible iron-iron bond, and iron spin state of the dinuclear tetra-hydrido complex [{5CpFe}2(μ-H)4] (1H, 5Cp = η5-C5 iPr5) by thoroughly accessing the geometric and electronic structure of this complex in comparison to the nonhydride reference [5CpCpFe] (1, Cp = C5H5). The so far observed most intense hydride induced signals in the pre-edge feature of the HERFD-XANES and in the VtC-XES spectra at the iron K-edge allow a precise analysis of the LUMO and HOMO states, respectively, by application of time-dependent density function theory (TD-DFT) and density functional theory (DFT) calculations. The results of these calculations are further employed to understand the oxidation state, spin states, and potential Fe-Fe bonds in this complex.
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Affiliation(s)
- Lukas Burkhardt
- Faculty of Science , Paderborn University , Warburger Straße 100 , 33098 Paderborn , Germany
| | - Carsten Mueller
- Department of Chemistry , University of Kaiserslautern , Erwin-Schrödinger-Straße 54 , 67663 Kaiserslautern , Germany
| | - Oliver A Groß
- Faculty of Science , Paderborn University , Warburger Straße 100 , 33098 Paderborn , Germany
| | - Yu Sun
- Department of Chemistry , University of Kaiserslautern , Erwin-Schrödinger-Straße 54 , 67663 Kaiserslautern , Germany
| | - Helmut Sitzmann
- Department of Chemistry , University of Kaiserslautern , Erwin-Schrödinger-Straße 54 , 67663 Kaiserslautern , Germany
| | - Matthias Bauer
- Faculty of Science , Paderborn University , Warburger Straße 100 , 33098 Paderborn , Germany.,Center for Sustainable Systems Design (CSSD) , Paderborn University , Warburger Straße 100 , 33098 Paderborn , Germany
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22
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Hanna L, Kucheryavy P, Lahanas N, Lockard JV. Spectroscopic characterization of metal ligation in trinuclear iron-μ 3-oxo-based complexes and metal-organic frameworks. J Chem Phys 2019; 150:174707. [DOI: 10.1063/1.5096796] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Affiliation(s)
- Lauren Hanna
- Department of Chemistry, Rutgers University—Newark, Newark, New Jersey 07102, USA
| | - Pavel Kucheryavy
- Department of Chemistry, Rutgers University—Newark, Newark, New Jersey 07102, USA
| | - Nicole Lahanas
- Department of Chemistry, Rutgers University—Newark, Newark, New Jersey 07102, USA
| | - Jenny V. Lockard
- Department of Chemistry, Rutgers University—Newark, Newark, New Jersey 07102, USA
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23
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Müller P, Neuba A, Flörke U, Henkel G, Kühne TD, Bauer M. Experimental and Theoretical High Energy Resolution Hard X-ray Absorption and Emission Spectroscopy on Biomimetic Cu 2S 2 Complexes. J Phys Chem A 2019; 123:3575-3581. [PMID: 30945858 DOI: 10.1021/acs.jpca.9b00463] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
High energy resolution fluorescence detected X-ray absorption near edge structure (HERFD-XANES) and Valence-to-Core X-ray emission (VtC-XES) spectroscopy are established as hard X-ray methods to investigate complexes that might be relevant as mimics for the biologically important CuA site. By investigation of three carefully selected complexes of the type [Cu2(NGuaS)2X2], characterized by a cyclic Cu2S2 core portion and a varying adjunct ligand nature, it is proven that the HERFD-XANES and VtC-XES measurements in combination with extensive TD-DFT calculations can reveal details of the electronic states in such complexes, including HOMO and LUMO levels and spin states. By theoretical spectroscopy, the value of this methodic combination for future in situ studies is demonstrated.
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Scheller JS, Irvine GW, Stillman MJ. Unravelling the mechanistic details of metal binding to mammalian metallothioneins from stoichiometric, kinetic, and binding affinity data. Dalton Trans 2018; 47:3613-3637. [PMID: 29431781 DOI: 10.1039/c7dt03319b] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Metallothioneins (MTs) are small, cysteine-rich proteins, found throughout Nature. Their ability to bind a number of different metals with a range of stoichiometric ratios means that this protein family is critically important for essential metal (Zn2+ and Cu+) homeostasis, metal storage, metal donation to nascent metalloenzymes as well as heavy metal detoxification. With its 20 cysteines, metallothionein is also considered to protect cells against oxidative stress. MT has been studied by a large number of researchers over the last 6 decades using a variety of spectroscopic techniques. The lack of distinguishing chromophores for the multitude of binding sites has made the evaluation of stoichiometric properties for different metals challenging. Initially, only 113Cd-NMR spectroscopy could provide strong evidence for the proposed cluster formation of Cd-MT. The extraordinary development of electrospray ionization mass spectrometry (ESI-MS), where all coexisting species in solution are observed, revolutionized MT research. Prior to the use of ESI-MS data, a range of "magic numbers" representing metal-to-MT molar ratios were reported from optical spectroscopic studies. The availability of ESI mass spectral data led to (i) the confirmation of cluster formation, (ii) a conceptual understanding of the cooperativity involved in multiple metal binding events, (iii) the presence of domain specificity between regions of the protein and (iv) mechanistic details involving both binding affinities and rate constants. The kinetic experiments identified the presence of multiple individual binding sites, each with a unique rate constant and an analogous binding affinity. The almost linear trend in rate constants as a function of bound As3+ provided a unique insight that became a critical step in the complete understanding of the mechanistic details of the metalation of MT. To fully define the biological function of this sulfur-rich protein it is necessary to determine kinetic rate constants and binding affinities for the essential metals. Recently, Zn2+ competition experiments between both of the isolated fragments (α and β) and the full-length protein (βα-MT 1a) as well as Zn2+ competition between βα-MT 1a and carbonic anhydrase were reported. From these data, the trend in binding affinities and the values of the Kf of the 7 bimolecular reactions involved in metalation were determined. From the analysis of ESI-MS data for Cu+ binding to βα-MT 1a at different pH-values, a trend in the 20 binding affinities for the complete metalation mechanism was reported. This review details a personal view of the historical development of the determination of stoichiometry for metal binding, the structure of the binding sites, the rates of the metalation reactions and the underlying binding affinities for each metalation step. We have attempted to summarize the experimental developments that led to the publication in May 2017 of the experimental determination of the 20 binding constants for the 20 sequential bimolecular reactions for Cu+ binding to the 20 Cys of apoMT as a function of pH that show the appearance and disappearance of clusters. We report both published data and in a series of tables an assembly of stoichiometries, and equilibrium constants for Zn2+ and Cu+ for many different metallothioneins.
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Affiliation(s)
- Judith S Scheller
- Department of Chemistry, The University of Western Ontario, London, Ontario N6A 5B7, Canada.
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Burkhardt L, Holzwarth M, Plietker B, Bauer M. Detection and Characterization of Hydride Ligands in Iron Complexes by High-Resolution Hard X-ray Spectroscopy and Implications for Catalytic Processes. Inorg Chem 2017; 56:13300-13310. [PMID: 29058447 DOI: 10.1021/acs.inorgchem.7b02063] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Two hydride catalysts [Fe(CO)(dppp)H(NO)] (dppp = 1,3-bis(diphenylphosphino)propane) and [Fe(CO)H(NO)(PPh3)2] in comparison with nonhydride analogues [Fe(dppe)(NO)2] (dppe = 1,3-bis(diphenylphosphino)ethane) and [Fe(NO)2(PPh3)2] are investigated with a combination of valence-to-core X-ray emission spectroscopy (VtC-XES) and high-energy resolution fluorescence detected X-ray absorption near-edge structure (HERFD-XANES). To fully understand the experiments and to obtain precise information about molecular levels being involved in the spectral signals, time-dependent density functional theory (TD-DFT) calculations and ground state density functional theory (DFT) calculations are necessary. An excellent agreement between experiment and theory allows the identification of particular spectral signals of the Fe-H group. Antibonding Fe-H interactions clearly contribute to pre-edge signals in HERFD-XANES spectra, while bonding Fe-H interactions cause characteristic signatures in the VtC-XES spectra. The sensitivity of both methods with respect to the Fe-H distance is demonstrated by a scanning simulation approach. The results open the way to study metal hydride complexes in situ, their formation, and their fate during catalytic reactions, using high-resolution XANES and valence-to-core X-ray emission spectroscopy.
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Affiliation(s)
- Lukas Burkhardt
- Department Chemie, Universität Paderborn , Warburger Straße 100, D-33098 Paderborn, Germany
| | - Michael Holzwarth
- Institut für Organische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Bernd Plietker
- Institut für Organische Chemie, Universität Stuttgart , Pfaffenwaldring 55, D-70569 Stuttgart, Germany
| | - Matthias Bauer
- Department Chemie, Universität Paderborn , Warburger Straße 100, D-33098 Paderborn, Germany
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26
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Rovira M, Roldán-Gómez S, Martin-Diaconescu V, Whiteoak CJ, Company A, Luis JM, Ribas X. Trifluoromethylation of a Well-Defined Square-Planar Aryl-Ni II Complex involving Ni III /CF 3. and Ni IV -CF 3 Intermediate Species. Chemistry 2017; 23:11662-11668. [PMID: 28685908 DOI: 10.1002/chem.201702168] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Indexed: 11/11/2022]
Abstract
Ni-mediated trifluoromethylation of an aryl-Br bond in model macrocyclic ligands (Ln -Br) has been thoroughly studied, starting with an oxidative addition at Ni0 to obtain well-defined aryl-NiII -Br complexes ([Ln -NiII ]Br). Abstraction of the halide with AgX (X=OTf- or ClO4- ) thereafter provides [Ln -NiII ](OTf). The nitrate analogue has been obtained through a direct C-H activation of an aryl-H bond using NiII salts, and this route has been studied by X-ray absorption spectroscopy (XAS). Crystallographic XRD and XAS characterization has shown a tight macrocyclic coordination in the aryl-NiII complex, which may hamper direct reaction with nucleophiles. On the contrary, enhanced reactivity is observed with oxidants, and the reaction of [Ln -NiII ](OTf) with CF3+ sources afforded Ln -CF3 products in quantitative yield. A combined experimental and theoretical mechanistic study provides new insights into the operative mechanism for this transformation. Computational analysis indicates the occurrence of an initial single electron transfer (SET) to 5-(trifluoromethyl)dibenzothiophenium triflate (TDTT), producing a transient L1 -NiIII /CF3. adduct, which rapidly recombines to form a [L1 -NiIV -CF3 ](X)2 intermediate species. A final facile reductive elimination affords L1 -CF3 . The well-defined square-planar model system studied here permits to gain fundamental knowledge on the rich redox chemistry of nickel, which is sought to facilitate the development of new Ni-based trifluoromethylation methodologies.
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Affiliation(s)
- Mireia Rovira
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
| | - Steven Roldán-Gómez
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
| | - Vlad Martin-Diaconescu
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
| | - Christopher J Whiteoak
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain.,Biomolecular Sciences Research Centre, Faculty of Health and Wellbeing, Sheffield Hallam University, City Campus, Sheffield, S1 1WB, UK
| | - Anna Company
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
| | - Josep M Luis
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
| | - Xavi Ribas
- Institut de Química Computacional i Catàlisi (IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Facultat Ciències, 17003, Girona, Catalonia, Spain
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Kline CD, Blackburn NJ. Substrate-Induced Carbon Monoxide Reactivity Suggests Multiple Enzyme Conformations at the Catalytic Copper M-Center of Peptidylglycine Monooxygenase. Biochemistry 2016; 55:6652-6661. [PMID: 27933800 DOI: 10.1021/acs.biochem.6b00845] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The present study uses CO as a surrogate for oxygen to probe how substrate binding triggers oxygen activation in peptidylglycine monooygenase (PHM). Infrared stretching frequencies (ν(C ≡ O)) of the carbonyl (CO) adducts of copper proteins are sensitive markers of Cu(I) coordination and are useful in probing oxygen reactivity because the electronic properties of O2 and CO are similar. The carbonyl chemistry has been explored using PHM WT and a number of active site variants in the absence and presence of peptidyl substrates. We have determined that upon carbonylation (i) a major CO band at 2092 cm-1 and a second minor CO band at 2063 cm-1 are observed in the absence of peptide substrate Ac-YVG; (ii) the presence of peptide substrate amplifies the minor CO band and causes it to partially interconvert with the CO band at 2092 cm-1; (iii) the substrate-induced CO band is associated with a second conformer at CuM; and (iv) the CuH-site mutants, which are inactive, fail to generate any substrate-induced CO bands. The total intensity of both bands is constant, suggesting that the Cu(I)M-site partitions between the two carbonylated enzyme states. Together, these data provide evidence for two conformers at CuM, one of which is induced by binding of the peptide substrate with the implication that this represents the conformation that also allows binding and activation of O2.
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Affiliation(s)
- Chelsey D Kline
- Institute of Environmental Health, Oregon Health and Science University , 3181 S.W. Sam Jackson Park Road, Portland, Oregon 97239, United States
| | - Ninian J Blackburn
- Institute of Environmental Health, Oregon Health and Science University , 3181 S.W. Sam Jackson Park Road, Portland, Oregon 97239, United States
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Kupper C, Rees JA, Dechert S, DeBeer S, Meyer F. Complete Series of {FeNO}(8), {FeNO}(7), and {FeNO}(6) Complexes Stabilized by a Tetracarbene Macrocycle. J Am Chem Soc 2016; 138:7888-98. [PMID: 27191681 DOI: 10.1021/jacs.6b00584] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Use of a macrocyclic tetracarbene ligand, which is topologically reminiscent of tetrapyrrole macrocycles though electronically distinct, has allowed for the isolation, X-ray crystallographic characterization and comprehensive spectroscopic investigation of a complete set of {FeNO}(x) complexes (x = 6, 7, 8). Electrochemical reduction, or chemical reduction with CoCp2, of the {FeNO}(7) complex 1 leads to the organometallic {FeNO}(8) species 2. Its crystallographic structure determination is the first for a nonheme iron nitroxyl {FeNO}(8) and has allowed to identify structural trends among the series of {FeNO}(x) complexes. Combined experimental data including (57)Fe Mössbauer, IR, UV-vis-NIR, NMR and Kβ X-ray emission spectroscopies in concert with DFT calculations suggest a largely metal centered reduction of 1 to form the low spin (S = 0) {FeNO}(8) species 2. The very strong σ-donor character of the tetracarbene ligand imparts unusual properties and spectroscopic signatures such as low (57)Fe Mössbauer isomer shifts and linear Fe-N-O units with high IR stretching frequencies for the NO ligand. The observed metal-centered reduction leads to distinct reactivity patterns of the {FeNO}(8) species. In contrast to literature reported {FeNO}(8) complexes, 2 does not undergo NO protonation under strictly anaerobic conditions. Only in the presence of both dioxygen and protons is rapid and clean oxidation to the {FeNO}(7) complex 1 observed. While 1 is stable toward dioxygen, its reaction with dioxygen under NO atmosphere forms the {FeNO}(6)(ONO) complex 3 that features an unusual O-nitrito ligand trans to the NO. 3 is a rare example of a nonheme octahedral {FeNO}(6) complex. Its electrochemical or chemical reduction triggers dissociation of the O-nitrito ligand and sequential formation of the {FeNO}(7) and {FeNO}(8) compounds 1 and 2. A consistent electronic structure picture has been derived for these unique organometallic variants of the key bioinorganic {FeNO}(x) functional units.
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Affiliation(s)
- Claudia Kupper
- Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany
| | - Julian A Rees
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.,Department of Chemistry, University of Washington , Box 351700, Seattle, Washington 98195-1700, United States
| | - Sebastian Dechert
- Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany
| | - Serena DeBeer
- Max Planck Institute for Chemical Energy Conversion , Stiftstrasse 34-36, D-45470 Mülheim an der Ruhr, Germany.,Department of Chemistry and Biochemistry, Cornell University , Ithaca, New York 14853, United States
| | - Franc Meyer
- Institut für Anorganische Chemie, Georg-August-Universität , Tammannstrasse 4, D-37077 Göttingen, Germany
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