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Transue WJ, Snyder RA, Caranto JD, Kurtz DM, Solomon EI. Particle Swarm Fitting of Spin Hamiltonians: Magnetic Circular Dichroism of Reduced and NO-Bound Flavodiiron Protein. Inorg Chem 2022; 61:16520-16527. [PMID: 36223761 PMCID: PMC9942269 DOI: 10.1021/acs.inorgchem.2c02234] [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
A particle swarm optimization (PSO) algorithm is described for the fitting of ground-state spin Hamiltonian parameters from variable-temperature/variable-field (VTVH) magnetic circular dichroism (MCD) data. This PSO algorithm is employed to define the ground state of two catalytic intermediates from a flavodiiron protein (FDP), a class of enzymes with nitric oxide reductase activity. The bimetallic iron active site of this enzyme proceeds through a biferrous intermediate and a mixed ferrous-{FeNO}7 intermediate during the catalytic cycle, and the MCD spectra of these intermediates are presented and analyzed. The fits of the spin Hamiltonians are shown to provide important geometric and electronic insight into these species that is compared and contrasted with previous reports.
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Affiliation(s)
| | - Rae Ana Snyder
- Department of Chemistry, Stanford University, Stanford, CA 94305
| | - Jonathan D. Caranto
- Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States
| | - Donald M. Kurtz
- Department of Chemistry, University of Texas at San Antonio, San Antonio, Texas 78249, United States
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2
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Koebke KJ, Pinter TBJ, Pitts WC, Pecoraro VL. Catalysis and Electron Transfer in De Novo Designed Metalloproteins. Chem Rev 2022; 122:12046-12109. [PMID: 35763791 PMCID: PMC10735231 DOI: 10.1021/acs.chemrev.1c01025] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
One of the hallmark advances in our understanding of metalloprotein function is showcased in our ability to design new, non-native, catalytically active protein scaffolds. This review highlights progress and milestone achievements in the field of de novo metalloprotein design focused on reports from the past decade with special emphasis on de novo designs couched within common subfields of bioinorganic study: heme binding proteins, monometal- and dimetal-containing catalytic sites, and metal-containing electron transfer sites. Within each subfield, we highlight several of what we have identified as significant and important contributions to either our understanding of that subfield or de novo metalloprotein design as a discipline. These reports are placed in context both historically and scientifically. General suggestions for future directions that we feel will be important to advance our understanding or accelerate discovery are discussed.
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Affiliation(s)
- Karl J. Koebke
- Department of Chemistry, University of Michigan Ann Arbor, MI 48109 USA
| | | | - Winston C. Pitts
- Department of Chemistry, University of Michigan Ann Arbor, MI 48109 USA
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3
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Foglia NO, Maganas D, Neese F. Going beyond the Electric-Dipole Approximation in the Calculation of Absorption and (Magnetic) Circular Dichroism Spectra including Scalar Relativistic and Spin-Orbit Coupling Effects. J Chem Phys 2022; 157:084120. [DOI: 10.1063/5.0094709] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
In this work, a time-dependent density functional theory (TD-DFT) scheme for computing optical spectroscopic properties in the framework of linearly and circularly polarized light is presented. The scheme is based on a previously formulated theory for predicting optical absorption and magnetic circular dichroism (MCD) spectra. The scheme operates in the framework of the full semi-classical field-matter interaction operator, thus generating a powerful and general computational scheme capable of computing the absorption (ABS), circular dichroism (CD), and MCD spectra. In addition, our implementation includes the treatment of relativistic effects in the framework of quasidegenerate perturbation theory, which accounts for scalar relativistic effects (in the self-consistent field step) and spin-orbit coupling (in the TD-DFT step), as well as external magnetic field perturbations. Hence, this formalism is also able to probe spin-forbidden transitions. The random orientations of molecules are taken into account by a semi-numerical approach involving a Lebedev numerical quadrature alongside analytical integration. It is demonstrated the numerical quadrature requires as few as 14 points for satisfactory converged results thus leading to a highly efficient scheme, while the calculation of the exact transition moments creates no computational bottlenecks. It is demonstrated that at zero magnetic field, the CD spectrum is recovered while the sum of left and right circularly polarized light contributions provides the linear absorption spectrum. The virtues of this efficient and general protocol are demonstrated on a selected set of organic molecules where the various contributions to the spectral intensities have been analyzed in detail.
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Affiliation(s)
- Nicolas Oscar Foglia
- Molecular Theory and Spectroscopy, Max-Planck-Institut für Kohlenforschung, Germany
| | | | - Frank Neese
- Molecular Theory and Spectroscopy, Max-Planck-Institut für Kohlenforschung, Germany
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4
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Adi LC, Santria A, Ishikawa N. Magnetic interaction of photoexcited terbium-porphyrin complexes with non-aromatic ligands having different symmetries. Dalton Trans 2022; 51:6186-6196. [PMID: 35383819 DOI: 10.1039/d2dt00306f] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Interaction between the total angular momentum (J) of 4f electrons in lanthanides and the orbital angular momentum (L) of porphyrins in the photoexcited states was investigated by temperature-dependent and magnetic circular dichroism (MCD) for 5,10,15,20-tetraphenylporphyrinato (TPP) terbium(III) complexes with two different non-aromatic ligands i.e. 12-crown-4(1,4,7,10-tetraoxacyclododecane) and 1-aza-12-crown-4(1,4,7-trioxa-10-azacyclododecane). The two cases with different ligands were examined in order to understand how magnetic interaction depends on the symmetry of the non-aromatic ligands. The three absorption bands in the visible region, B(0,0), Q(1,0), and Q(0,0) bands, showed temperature-dependent MCD A term. For each band, the J-L interaction was determined from the simulation-based fitting to experimental ratios. An increase in the magnitude of the J-L interaction was observed when the second ligand was the aza-crown with a lower symmetry. Ab initio RASSCF/RASSI calculations were performed to explore the effect of the difference in the second ligand to the ligand centred excited states and the ligand-field-splitting structure on the metal-centred ground multiplet of J = 6.
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Affiliation(s)
- Langit Cahya Adi
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
| | - Anas Santria
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan. .,National Research and Innovation Agency, Jalan M.H. Thamrin No. 8, Jakarta Pusat, Jakarta 10340, Indonesia
| | - Naoto Ishikawa
- Department of Chemistry, Graduate School of Science, Osaka University, 1-1 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.
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5
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Lehnert N, Kim E, Dong HT, Harland JB, Hunt AP, Manickas EC, Oakley KM, Pham J, Reed GC, Alfaro VS. The Biologically Relevant Coordination Chemistry of Iron and Nitric Oxide: Electronic Structure and Reactivity. Chem Rev 2021; 121:14682-14905. [PMID: 34902255 DOI: 10.1021/acs.chemrev.1c00253] [Citation(s) in RCA: 92] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Nitric oxide (NO) is an important signaling molecule that is involved in a wide range of physiological and pathological events in biology. Metal coordination chemistry, especially with iron, is at the heart of many biological transformations involving NO. A series of heme proteins, nitric oxide synthases (NOS), soluble guanylate cyclase (sGC), and nitrophorins, are responsible for the biosynthesis, sensing, and transport of NO. Alternatively, NO can be generated from nitrite by heme- and copper-containing nitrite reductases (NIRs). The NO-bearing small molecules such as nitrosothiols and dinitrosyl iron complexes (DNICs) can serve as an alternative vehicle for NO storage and transport. Once NO is formed, the rich reaction chemistry of NO leads to a wide variety of biological activities including reduction of NO by heme or non-heme iron-containing NO reductases and protein post-translational modifications by DNICs. Much of our understanding of the reactivity of metal sites in biology with NO and the mechanisms of these transformations has come from the elucidation of the geometric and electronic structures and chemical reactivity of synthetic model systems, in synergy with biochemical and biophysical studies on the relevant proteins themselves. This review focuses on recent advancements from studies on proteins and model complexes that not only have improved our understanding of the biological roles of NO but also have provided foundations for biomedical research and for bio-inspired catalyst design in energy science.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Eunsuk Kim
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Hai T Dong
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Jill B Harland
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Andrew P Hunt
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Elizabeth C Manickas
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Kady M Oakley
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - John Pham
- Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
| | - Garrett C Reed
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Victor Sosa Alfaro
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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6
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Herbert PJ, Knappenberger KL. Spin-Polarized Photoluminescence in Au 25 (SC 8 H 9 ) 18 Monolayer-Protected Clusters. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2021; 17:e2004431. [PMID: 33511771 DOI: 10.1002/smll.202004431] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/22/2020] [Revised: 11/01/2020] [Indexed: 06/12/2023]
Abstract
Here, the observation of spin-polarized emission for the Au25 (SC8 H9 )18 monolayer-protected cluster (MPC) is reported. Variable-temperature variable-field magnetic circular photoluminescence (VTV H ⇀ -MCPL) measurements are combined with VT-PL spectroscopy to provide state-resolved characterization of the transient electronic structure and spin-polarized electron-hole recombination dynamics of Au25 (SC8 H9 )18 . Through analysis of VTV H ⇀ -MCPL measurements, a low energy (1.64 eV) emission peak is assigned to intraband relaxation between core-metal-localized superatom-D to -P orbitals. Two higher energy interband components (1.78 eV, 1.94 eV) are assigned to relaxation from superatom-D orbitals to states localized to the inorganic semirings. For both intraband superatom-based or interband relaxation mechanisms, the extent of spin-polarization, quantified as the degree of circular polarization (DOCP), is determined by state-specific electron-vibration coupling strengths and energy separations of bright and dark electronic fine-structure levels. At low temperatures (<60 K), metal-metal superatom-based intraband transitions dominate the global PL emission. At higher temperatures (>60 K), interband ligand-based emission is dominant. In the low-temperature PL regime, increased sample temperature results in larger global PL intensity. In the high-temperature regime, increased temperature quenches interband radiative recombination. The relative intensity for each PL mechanism is discussed in terms of state-specific electronic-vibrational coupling strengths and related to the total angular momentum, quantified by Landé g-factors.
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Affiliation(s)
- Patrick J Herbert
- Department of Chemistry, The Pennsylvania University, University Park, PA, 16802, USA
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7
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Ostrovsky S, Tomkowicz Z, Foro S, Reedijk J, Haase W. Magneto-optical study of the zero-field splitting in a mononuclear tetrahedrally coordinated Co(II) compound with a mixed ligand surrounding. Polyhedron 2020. [DOI: 10.1016/j.poly.2020.114630] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Pinter TBJ, Koebke KJ, Pecoraro VL. Catalysis and Electron Transfer in De Novo Designed Helical Scaffolds. Angew Chem Int Ed Engl 2020; 59:7678-7699. [PMID: 31441170 PMCID: PMC7035182 DOI: 10.1002/anie.201907502] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2019] [Indexed: 12/31/2022]
Abstract
The relationship between protein structure and function is one of the greatest puzzles within biochemistry. De novo metalloprotein design is a way to wipe the board clean and determine what is required to build in function from the ground up in an unrelated structure. This Review focuses on protein design efforts to create de novo metalloproteins within alpha-helical scaffolds. Examples of successful designs include those with carbonic anhydrase or nitrite reductase activity by incorporating a ZnHis3 or CuHis3 site, or that recapitulate the spectroscopic properties of unique electron-transfer sites in cupredoxins (CuHis2 Cys) or rubredoxins (FeCys4 ). This work showcases the versatility of alpha helices as scaffolds for metalloprotein design and the progress that is possible through careful rational design. Our studies cover the invariance of carbonic anhydrase activity with different site positions and scaffolds, refinement of our cupredoxin models, and enhancement of nitrite reductase activity up to 1000-fold.
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Affiliation(s)
- Tyler B. J. Pinter
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States, 48109-1055
| | - Karl J. Koebke
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States, 48109-1055
| | - Vincent L. Pecoraro
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan, United States, 48109-1055
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9
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Pinter TBJ, Koebke KJ, Pecoraro VL. Katalyse und Elektronentransfer in helikalen De‐novo‐Gerüststrukturen. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201907502] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Tyler B. J. Pinter
- Department of Chemistry University of Michigan Ann Arbor Michigan 48109-1055 USA
| | - Karl J. Koebke
- Department of Chemistry University of Michigan Ann Arbor Michigan 48109-1055 USA
| | - Vincent L. Pecoraro
- Department of Chemistry University of Michigan Ann Arbor Michigan 48109-1055 USA
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10
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Fleischauer VE, Ganguly G, Woen DH, Wolford NJ, Evans WJ, Autschbach J, Neidig ML. Insight into the Electronic Structure of Formal Lanthanide(II) Complexes using Magnetic Circular Dichroism Spectroscopy. Organometallics 2019. [DOI: 10.1021/acs.organomet.9b00315] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Valerie E. Fleischauer
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - Gaurab Ganguly
- Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14206-3000, United States
| | - David H. Woen
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Nikki J. Wolford
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
| | - William J. Evans
- Department of Chemistry, University of California, Irvine, California 92697-2025, United States
| | - Jochen Autschbach
- Department of Chemistry, University at Buffalo, State University of New York, Buffalo, New York 14206-3000, United States
| | - Michael L. Neidig
- Department of Chemistry, University of Rochester, Rochester, New York 14627, United States
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11
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Manesis AC, Musselman BW, Keegan BC, Shearer J, Lehnert N, Shafaat HS. A Biochemical Nickel(I) State Supports Nucleophilic Alkyl Addition: A Roadmap for Methyl Reactivity in Acetyl Coenzyme A Synthase. Inorg Chem 2019; 58:8969-8982. [PMID: 30788970 PMCID: PMC6635881 DOI: 10.1021/acs.inorgchem.8b03546] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
![]()
Nickel-containing
enzymes such as methyl coenzyme M reductase (MCR) and carbon monoxide
dehydrogenase/acetyl coenzyme A synthase (CODH/ACS) play a critical
role in global energy conversion reactions, with significant contributions
to carbon-centered processes. These enzymes are implied to cycle through
a series of nickel-based organometallic intermediates during catalysis,
though identification of these intermediates remains challenging.
In this work, we have developed and characterized a nickel-containing
metalloprotein that models the methyl-bound organometallic intermediates
proposed in the native enzymes. Using a nickel(I)-substituted azurin
mutant, we demonstrate that alkyl binding occurs via nucleophilic
addition of methyl iodide as a methyl donor. The paramagnetic NiIII-CH3 species initially generated can be rapidly
reduced to a high-spin NiII-CH3 species in the
presence of exogenous reducing agent, following a reaction sequence
analogous to that proposed for ACS. These two distinct bioorganometallic
species have been characterized by optical, EPR, XAS, and MCD spectroscopy,
and the overall mechanism describing methyl reactivity with nickel
azurin has been quantitatively modeled using global kinetic simulations.
A comparison between the nickel azurin protein system and existing
ACS model compounds is presented. NiIII-CH3 Az
is only the second example of two-electron addition of methyl iodide
to a NiI center to give an isolable species and the first
to be formed in a biologically relevant system. These results highlight
the divergent reactivity of nickel across the two intermediates, with
implications for likely reaction mechanisms and catalytically relevant
states in the native ACS enzyme. A bioorganometallic model
for acetyl coenzyme A synthase has been developed. This model protein
is able to bind a cationic methyl group via direct addition to the
nickel(I) center. The resultant nickel(III)-methyl species has been
characterized via optical and electron paramagnetic resonance spectroscopy,
and the reduced nickel(II)-methyl state has been characterized using
magnetic circular dichroism and X-ray spectroscopy. Implications for
further reactivity with CO are gleaned from electronic structure analysis
of the nickel-methyl species.
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Affiliation(s)
- Anastasia C Manesis
- Department of Chemistry and Biochemistry , The Ohio State University , 100 W. 18th Avenue , Columbus , Ohio 43210 , United States
| | - Bradley W Musselman
- Department of Chemistry , University of Michigan , 930 N. University Avenue , Ann Arbor , Michigan 48109 , United States
| | - Brenna C Keegan
- Department of Chemistry , Trinity University , One Trinity Place , San Antonio , Texas 78212 , United States
| | - Jason Shearer
- Department of Chemistry , Trinity University , One Trinity Place , San Antonio , Texas 78212 , United States
| | - Nicolai Lehnert
- Department of Chemistry , University of Michigan , 930 N. University Avenue , Ann Arbor , Michigan 48109 , United States
| | - Hannah S Shafaat
- Department of Chemistry and Biochemistry , The Ohio State University , 100 W. 18th Avenue , Columbus , Ohio 43210 , United States
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12
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Tebo AG, Pinter TBJ, García-Serres R, Speelman AL, Tard C, Sénéque O, Blondin G, Latour JM, Penner-Hahn J, Lehnert N, Pecoraro VL. Development of a Rubredoxin-Type Center Embedded in a de Dovo-Designed Three-Helix Bundle. Biochemistry 2018; 57:2308-2316. [PMID: 29561598 DOI: 10.1021/acs.biochem.8b00091] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Protein design is a powerful tool for interrogating the basic requirements for the function of a metal site in a way that allows for the selective incorporation of elements that are important for function. Rubredoxins are small electron transfer proteins with a reduction potential centered near 0 mV (vs normal hydrogen electrode). All previous attempts to design a rubredoxin site have focused on incorporating the canonical CXXC motifs in addition to reproducing the peptide fold or using flexible loop regions to define the morphology of the site. We have produced a rubredoxin site in an utterly different fold, a three-helix bundle. The spectra of this construct mimic the ultraviolet-visible, Mössbauer, electron paramagnetic resonance, and magnetic circular dichroism spectra of native rubredoxin. Furthermore, the measured reduction potential suggests that this rubredoxin analogue could function similarly. Thus, we have shown that an α-helical scaffold sustains a rubredoxin site that can cycle with the desired potential between the Fe(II) and Fe(III) states and reproduces the spectroscopic characteristics of this electron transport protein without requiring the classic rubredoxin protein fold.
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Affiliation(s)
- Alison G Tebo
- Program in Chemical Biology , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Tyler B J Pinter
- Department of Chemistry and Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Ricardo García-Serres
- Université Grenoble Alpes, CNRS, CEA, BIG, LCBM (UMR 5249), F-38054 Grenoble , France
| | - Amy L Speelman
- Department of Chemistry and Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Cédric Tard
- LCM, CNRS, École Polytechnique, Université Paris-Saclay, 91128 Palaiseau Cedex, France
| | - Olivier Sénéque
- Université Grenoble Alpes, CNRS, CEA, BIG, LCBM (UMR 5249), F-38054 Grenoble , France
| | - Geneviève Blondin
- Université Grenoble Alpes, CNRS, CEA, BIG, LCBM (UMR 5249), F-38054 Grenoble , France
| | - Jean-Marc Latour
- Université Grenoble Alpes, CNRS, CEA, BIG, LCBM (UMR 5249), F-38054 Grenoble , France
| | - James Penner-Hahn
- Department of Chemistry and Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Nicolai Lehnert
- Department of Chemistry and Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Vincent L Pecoraro
- Program in Chemical Biology , University of Michigan , Ann Arbor , Michigan 48109 , United States.,Department of Chemistry and Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
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13
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Herbert PJ, Mitra U, Knappenberger KL. Variable-temperature variable-field magnetic circular photoluminescence (VTVH-MCPL) spectroscopy for electronic-structure determination in nanoscale chemical systems. OPTICS LETTERS 2017; 42:4833-4836. [PMID: 29216123 DOI: 10.1364/ol.42.004833] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 10/25/2017] [Indexed: 06/07/2023]
Abstract
In this Letter, we describe variable-temperature variable-field magnetic circular photoluminescence (VTVH-MCPL) spectroscopy as a complementary technique to absorption-based magnetic circular dichroism. A paramagnetic model system, Au25(SC8H9)18, is chosen to demonstrate the information content that is obtained from VTVH-MCPL. Specifically, the methods and analyses for the determination of electronic Landé g-factors, zero-field energy splittings, and relative A-, B-, and C-term contributions to the MCPL response are detailed. The determination of these system properties from photoluminescence data suggests the feasibility of point-source-based super-resolution magneto-optical microscopy.
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14
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Suturina EA, Nehrkorn J, Zadrozny JM, Liu J, Atanasov M, Weyhermüller T, Maganas D, Hill S, Schnegg A, Bill E, Long JR, Neese F. Magneto-Structural Correlations in Pseudotetrahedral Forms of the [Co(SPh)4]2– Complex Probed by Magnetometry, MCD Spectroscopy, Advanced EPR Techniques, and ab Initio Electronic Structure Calculations. Inorg Chem 2017; 56:3102-3118. [DOI: 10.1021/acs.inorgchem.7b00097] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Elizaveta A. Suturina
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
- Novosibirsk State University, Pirogova 2, 630090 Novosibirsk, Russia
| | - Joscha Nehrkorn
- Berlin Joint EPR Lab, Institute for Nanospectroscopy, Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstraße
5, 12489 Berlin, Germany
| | - Joseph M. Zadrozny
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
| | - Junjie Liu
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
- Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1
3PU, United Kingdom
| | - Mihail Atanasov
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
- Bulgarian Academy of Sciences, Institute of General and Inorganic
Chemistry, Akad. Georgi
Bontchev Street 11, 1113 Sofia, Bulgaria
| | - Thomas Weyhermüller
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
| | - Dimitrios Maganas
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
| | - Stephen Hill
- National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
- Department of Physics, Florida State University, Tallahassee, Florida 32306, United States
| | - Alexander Schnegg
- Berlin Joint EPR Lab, Institute for Nanospectroscopy, Helmholtz-Zentrum Berlin für Materialien und Energie, Kekuléstraße
5, 12489 Berlin, Germany
| | - Eckhard Bill
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
| | - Jeffrey R. Long
- Department of Chemistry, University of California Berkeley, Berkeley, California 94720, United States
| | - Frank Neese
- Max Planck Institute for Chemical Energy Conversion, Stiftstraße 34-36, Mülheim an der Ruhr 45470, Germany
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15
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Ye S, Kupper C, Meyer S, Andris E, Navrátil R, Krahe O, Mondal B, Atanasov M, Bill E, Roithová J, Meyer F, Neese F. Magnetic Circular Dichroism Evidence for an Unusual Electronic Structure of a Tetracarbene-Oxoiron(IV) Complex. J Am Chem Soc 2016; 138:14312-14325. [PMID: 27682505 DOI: 10.1021/jacs.6b07708] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In biology, high valent oxo-iron(IV) species have been shown to be pivotal intermediates for functionalization of C-H bonds in the catalytic cycles of a range of O2-activating iron enzymes. This work details an electronic-structure investigation of [FeIV(O)(LNHC)(NCMe)]2+ (LNHC = 3,9,14,20-tetraaza-1,6,12,17-tetraazoniapenta-cyclohexacosane-1(23),4,6(26),10,12(25),15,17(24),21-octaene, complex 1) using helium tagging infrared photodissociation (IRPD), absorption, and magnetic circular dichroism (MCD) spectroscopy, coupled with DFT and highly correlated wave function based multireference calculations. The IRPD spectrum of complex 1 reveals the Fe-O stretching vibration at 832 ± 3 cm-1. By analyzing the Franck-Condon progression, we can determine the same vibration occurring at 616 ± 10 cm-1 in the E(dxy → dxz,yz) excited state. Both values are similar to those measured for [FeIV(O)(TMC)(NCMe)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane). The low-temperature MCD spectra of complex 1 exhibit three pseudo A-term signals around 12 500, 17 000, and 24 300 cm-1. We can unequivocally assign them to the ligand field transitions of dxy → dxz,yz, dxz,yz → dz2, and dxz,yz → dx2-y2, respectively, through direct calculations of MCD spectra and independent determination of the MCD C-term signs from the corresponding electron donating and accepting orbitals. In comparison with the corresponding transitions observed for [FeIV(O) (SR-TPA)(NCMe)]2+ (SR-TPA = tris(3,5-dimethyl-4-methoxypyridyl-2-methy)amine), the excitations within the (FeO)2+ core of complex 1 have similar transition energies, whereas the excitation energy for dxz,yz → dx2-y2 is significantly higher (∼12 000 cm-1 for [FeIV(O)(SR-TPA)(NCMe)]2+). Our results thus substantiate that the tetracarbene ligand (LNHC) of complex 1 does not significantly affect the bonding in the (FeO)2+ unit but strongly destabilizes the dx2-y2 orbital to eventually lift it above dz2. As a consequence, this unusual electron configuration leads to an unprecedentedly larger quintet-triplet energy separation for complex 1, which largely rules out the possibility that the H atom transfer reaction may take place on the quintet surface and hence quenches two-state reactivity. The resulting mechanistic implications are discussed.
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Affiliation(s)
- Shengfa Ye
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Claudia Kupper
- Institut für Anorganische Chemie, Georg-August-Universität Göttingen , Tammannstr. 4, D-37077 Göttingen, Germany
| | - Steffen Meyer
- Institut für Anorganische Chemie, Georg-August-Universität Göttingen , Tammannstr. 4, D-37077 Göttingen, Germany
| | - Erik Andris
- Department of Organic Chemistry, Faculty of Science, Charles University in Prague , Hlavova 8, 128 43 Praha 2, Czech Republic
| | - Rafael Navrátil
- Department of Organic Chemistry, Faculty of Science, Charles University in Prague , Hlavova 8, 128 43 Praha 2, Czech Republic
| | - Oliver Krahe
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Bhaskar Mondal
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Mihail Atanasov
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany.,Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences , 1113 Sofia, Bulgaria
| | - Eckhard Bill
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
| | - Jana Roithová
- Department of Organic Chemistry, Faculty of Science, Charles University in Prague , Hlavova 8, 128 43 Praha 2, Czech Republic
| | - Franc Meyer
- Institut für Anorganische Chemie, Georg-August-Universität Göttingen , Tammannstr. 4, D-37077 Göttingen, Germany
| | - Frank Neese
- Max-Planck Institut für Chemische Energiekonversion, Stiftstr. 34-36, D-45470 Mülheim an der Ruhr, Germany
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Colmer HE, Margarit CG, Smith JM, Jackson TA, Telser J. Spectroscopic and Computational Investigation of Low-Spin Mn(III) Bis(scorpionate) Complexes. Eur J Inorg Chem 2016; 2016:2413-2423. [PMID: 28713219 PMCID: PMC5507630 DOI: 10.1002/ejic.201501250] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2015] [Indexed: 11/06/2022]
Abstract
Six-coordinate MnIII complexes are typically high-spin (S = 2), however, the scorpionate ligand, both in its traditional, hydridotris(pyrazolyl)borate form, Tp- and Tp*- (the latter with 3,5-dimethylpyrazole substituents) and in an aryltris(carbene)borate (i.e., N-heterocyclic carbene, NHC) form, [Ph(MeIm)3B]-, (MeIm = 3-methylimidazole) lead to formation of bis(scorpionate) complexes of MnIII with spin triplet ground states; three of which were investigated herein: [Tp2Mn]SbF6 (1SBF6), [Tp*2Mn]SbF6 (2SBF6), and [{Ph(MeIm)3B}2Mn]CF3SO3 (3CF3SO3). These trigonally symmetric complexes were studied experimentally by magnetic circular dichroism (MCD) spectroscopy (the propensity of 3 to oxidize to MnIV precluded collection of useful MCD data) including variable temperatures and fields (VTVH-MCD) and computationally by ab initio CASSCF/NEVPT2 methods. These combined experimental and theoretical techniques establish the 3A2g electronic ground state for the three complexes, and provide information on the energy of the "conventional" high-spin excited state (5Eg) and other, triplet excited states. These results show the electronic effect of pyrazole ring substituents in comparing 1 and 2. The tunability of the scorpionate ligand, even by perhaps the simplest change (from pyrazole in 1 to 3,5-dimethylpyrazole in 2) is quantitatively manifested through perturbations in ligand-field excited-state energies that impact ground-state zero-field splittings. The comparison with the NHC donor is much more dramatic. In 3, the stronger σ-donor properties of the NHC lead to a quantitatively different electronic structure, so that the lowest lying spin triplet excited state, 3Eg, is much closer in energy to the ground state than in 1 or 2. The zero-field splitting (zfs) parameters of the three complexes were calculated and in the case of 1 and 2 compare closely to experiment (lower by < 10%, < 2 cm-1 in absolute terms); for 3 the large magnitude zfs is reproduced, although there is ambiguity about its sign. The comprehensive picture obtained for these bis(scorpionate) MnIII complexes provides quantitative insight into the role played by the scorpionate ligand in stabilizing unusual electronic structures.
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Affiliation(s)
- Hannah E Colmer
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 USA
| | - Charles G Margarit
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003 USA
| | - Jeremy M Smith
- Department of Chemistry and Biochemistry, New Mexico State University, Las Cruces, New Mexico 88003 USA
- Department of Chemistry, Indiana University, Bloomington, Indiana 47405 USA
| | - Timothy A Jackson
- Department of Chemistry, University of Kansas, Lawrence, Kansas 66045 USA
| | - Joshua Telser
- Department of Biological, Chemical and Physical Sciences, Roosevelt University, Chicago, Illinois 60605 USA
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Leto DF, Massie AA, Colmer HE, Jackson TA. X-Band Electron Paramagnetic Resonance Comparison of Mononuclear Mn(IV)-oxo and Mn(IV)-hydroxo Complexes and Quantum Chemical Investigation of Mn(IV) Zero-Field Splitting. Inorg Chem 2016; 55:3272-82. [PMID: 27002928 DOI: 10.1021/acs.inorgchem.5b02309] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
X-band electron paramagnetic resonance (EPR) spectroscopy was used to probe the ground-state electronic structures of mononuclear Mn(IV) complexes [Mn(IV)(OH)2(Me2EBC)](2+) and [Mn(IV)(O)(OH)(Me2EBC)](+). These compounds are known to effect C-H bond oxidation reactions by a hydrogen-atom transfer mechanism. They provide an ideal system for comparing Mn(IV)-hydroxo versus Mn(IV)-oxo motifs, as they differ by only a proton. Simulations of 5 K EPR data, along with analysis of variable-temperature EPR signal intensities, allowed for the estimation of ground-state zero-field splitting (ZFS) and (55)Mn hyperfine parameters for both complexes. From this analysis, it was concluded that the Mn(IV)-oxo complex [Mn(IV)(O)(OH)(Me2EBC)](+) has an axial ZFS parameter D (D = +1.2(0.4) cm(-1)) and rhombicity (E/D = 0.22(1)) perturbed relative to the Mn(IV)-hydroxo analogue [Mn(IV)(OH)2(Me2EBC)](2+) (|D| = 0.75(0.25) cm(-1); E/D = 0.15(2)), although the complexes have similar (55)Mn values (a = 7.7 and 7.5 mT, respectively). The ZFS parameters for [Mn(IV)(OH)2(Me2EBC)](2+) were compared with values obtained previously through variable-temperature, variable-field magnetic circular dichroism (VTVH MCD) experiments. While the VTVH MCD analysis can provide a reasonable estimate of the magnitude of D, the E/D values were poorly defined. Using the ZFS parameters reported for these complexes and five other mononuclear Mn(IV) complexes, we employed coupled-perturbed density functional theory (CP-DFT) and complete active space self-consistent field (CASSCF) calculations with second-order n-electron valence-state perturbation theory (NEVPT2) correction, to compare the ability of these two quantum chemical methods for reproducing experimental ZFS parameters for Mn(IV) centers. The CP-DFT approach was found to provide reasonably acceptable values for D, whereas the CASSCF/NEVPT2 method fared worse, considerably overestimating the magnitude of D in several cases. Both methods were poor in reproducing experimental E/D values. Overall, this work adds to the limited investigations of Mn(IV) ground-state properties and provides an initial assessment for calculating Mn(IV) ZFS parameters with quantum chemical methods.
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Affiliation(s)
- Domenick F Leto
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Allyssa A Massie
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Hannah E Colmer
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
| | - Timothy A Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas , 1251 Wescoe Hall Drive, Lawrence, Kansas 66045, United States
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Ye S, Xue G, Krivokapic I, Petrenko T, Bill E, Que Jr L, Neese F. Magnetic circular dichroism and computational study of mononuclear and dinuclear iron(IV) complexes. Chem Sci 2015; 6:2909-2921. [PMID: 26417426 PMCID: PMC4583211 DOI: 10.1039/c4sc03268c] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 02/26/2015] [Indexed: 12/13/2022] Open
Abstract
High-valent iron(IV)-oxo species are key intermediates in the catalytic cycles of a range of O2-activating iron enzymes. This work presents a detailed study of the electronic structures of mononuclear ([FeIV(O)(L)(NCMe)]2+, 1, L = tris(3,5-dimethyl-4-methoxylpyridyl-2-methyl)amine) and dinuclear ([(L)FeIV(O)(μ-O)FeIV(OH)(L)]3+, 2) iron(IV) complexes using absorption (ABS), magnetic circular dichroism (MCD) spectroscopy and wave-function-based quantum chemical calculations. For complex 1, the experimental MCD spectra at 2-10 K are dominated by a broad positive C-term band between 12000 and 18000 cm-1. As the temperature increases up to ~20 K, this feature is gradually replaced by a derivative-shaped signal. The computed MCD spectra are in excellent agreement with experiment, which reproduce not only the excitation energies and the MCD signs of key transitions but also their temperature-dependent intensity variations. To further corroborate the assignments suggested by the calculations, the individual MCD sign for each transition is independently determined from the corresponding electron donating and accepting orbitals. Thus, unambiguous assignments can be made for the observed transitions in 1. The ABS/MCD data of complex 2 exhibit ten features that are assigned as ligand-field transitions or oxo- or hydroxo-to-metal charge transfer bands, based on MCD/ABS intensity ratios, calculated excitation energies, polarizations, and MCD signs. In comparison with complex 1, the electronic structure of the FeIV=O site is not significantly perturbed by the binding to another iron(IV) center. This may explain the experimental finding that complexes 1 and 2 have similar reactivities toward C-H bond activation and O-atom transfer.
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Affiliation(s)
- Shengfa Ye
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Genqiang Xue
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , Minnesota 55455 , USA .
| | - Itana Krivokapic
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Taras Petrenko
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Eckhard Bill
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
| | - Lawrence Que Jr
- Department of Chemistry , Center for Metals in Biocatalysis , University of Minnesota , 207 Pleasant St. SE , Minneapolis , Minnesota 55455 , USA .
| | - Frank Neese
- Max-Planck Institut für Chemische Energiekonversion , Stiftstraße 34-36 , D-45470 Mülheim an der Ruhr , Germany . ; ;
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Colmer HE, Geiger RA, Leto DF, Wijeratne GB, Day VW, Jackson TA. Geometric and electronic structure of a peroxomanganese(III) complex supported by a scorpionate ligand. Dalton Trans 2014; 43:17949-63. [PMID: 25312785 PMCID: PMC4237624 DOI: 10.1039/c4dt02483d] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the Mn(III)-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz(2) MO that is the donor MO for this transition.
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Affiliation(s)
- Hannah E Colmer
- Department of Chemistry, University of Kansas, 1251 Wescoe Hall Drive, Lawrence, KS 66045, USA.
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20
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Jackson TA, Gutman CT, Maliekal J, Miller AF, Brunold TC. Geometric and electronic structures of manganese-substituted iron superoxide dismutase. Inorg Chem 2013; 52:3356-67. [PMID: 23461587 PMCID: PMC3974275 DOI: 10.1021/ic302867y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The active-site structures of the oxidized and reduced forms of manganese-substituted iron superoxide dismutase (Mn(Fe)SOD) are examined, for the first time, using a combination of spectroscopic and computational methods. On the basis of electronic absorption, circular dichroism (CD), magnetic CD (MCD), and variable-temperature variable-field MCD data obtained for oxidized Mn(Fe)SOD, we propose that the active site of this species is virtually identical to that of wild-type manganese SOD (MnSOD), with both containing a metal ion that resides in a trigonal bipyramidal ligand environment. This proposal is corroborated by quantum mechanical/molecular mechanical (QM/MM) computations performed on complete protein models of Mn(Fe)SOD in both its oxidized and reduced states and, for comparison, wild-type (WT) MnSOD. The major differences between the QM/MM optimized active sites of WT MnSOD and Mn(Fe)SOD are a smaller (His)N-Mn-N(His) equatorial angle and a longer (Gln146(69))NH···O(sol) H-bond distance in the metal-substituted protein. Importantly, these modest geometric differences are consistent with our spectroscopic data obtained for the oxidized proteins and high-field electron paramagnetic resonance spectra reported previously for reduced Mn(Fe)SOD and MnSOD. As Mn(Fe)SOD exhibits a reduction midpoint potential (E(m)) almost 700 mV higher than that of MnSOD, which has been shown to be sufficient for explaining the lack of SOD activity displayed by the metal-subtituted species (Vance, C. K.; Miller, A. F. Biochemistry 2001, 40, 13079-13087), E(m)'s were computed for our experimentally validated QM/MM optimized models of Mn(Fe)SOD and MnSOD. These computations properly reproduce the experimental trend and reveal that the drastically elevated E(m) of the metal substituted protein stems from a larger separation between the second-sphere Gln residue and the coordinated solvent in Mn(Fe)SOD relative to MnSOD, which causes a weakening of the corresponding H-bond interaction in the oxidized state and alleviates steric crowding in the reduced state.
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Affiliation(s)
| | | | - James Maliekal
- Department of Chemistry, University of Kentucky, Lexington, KY 40506
| | | | - Thomas C. Brunold
- To whom correspondence should be addressed: 1101 University Ave., Madison, WI 53706, phone: (608) 265-9056, fax: (608) 262-6143,
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Tomkowicz Z, Ostrovsky S, Foro S, Calvo-Perez V, Haase W. Magnetooptical and Structural Investigations of Five Dimeric Cobalt(II) Complexes Mimicking Metalloenzyme Active Sites. Inorg Chem 2012; 51:6046-55. [DOI: 10.1021/ic202529p] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Z. Tomkowicz
- Eduard-Zintl-Institute
of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287
Darmstadt, Germany
- Institute of Physics, Jagiellonian University, Reymonta 4,
30-059 Kraków, Poland
| | - S. Ostrovsky
- Eduard-Zintl-Institute
of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287
Darmstadt, Germany
- Institute of Applied
Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova
| | - S. Foro
- Clemens-Schoepf-Institute
of Organic Chemistry and Biochemistry, Darmstadt University of Technology, Petersenstrasse 23, 64287
Darmstadt, Germany
| | - V. Calvo-Perez
- Facultad Ciencias
Químicas y Farmacéuticas, Universidad de Chile, Casilla 233, Santiago, Chile
| | - W. Haase
- Eduard-Zintl-Institute
of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287
Darmstadt, Germany
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Lehnert N. Elucidating second coordination sphere effects in heme proteins using low-temperature magnetic circular dichroism spectroscopy. J Inorg Biochem 2012; 110:83-93. [PMID: 22516139 DOI: 10.1016/j.jinorgbio.2012.02.033] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2011] [Revised: 02/27/2012] [Accepted: 02/28/2012] [Indexed: 11/29/2022]
Abstract
This paper reviews recent findings on how the second coordination sphere of heme proteins fine-tunes the properties of the heme active site via hydrogen bonding. This insight is obtained from low-temperature magnetic circular dichroism (MCD) spectroscopy. In the case of high-spin ferric hemes, MCD spectroscopy allows for the identification of a multitude of charge-transfer (CT) transitions. Using optically-detected magnetic saturation curves, out-of-plane polarized CT transitions between the heme and its axial ligand(s) can be identified. In the case of ferric Cytochrome P450cam, the corresponding S(σ)→Fe(III) CT transition can be used as a probe for the {Fe(III)-axial ligand} interaction, indicating that the hydrogen bonding network of the proximal Cys only plays a limited role for fine-tuning the Fe(III)-S(Cys) interaction. In the case of high-spin ferrous hemes with axial His/imidazole coordination, our MCD-spectroscopic investigations have uncovered a direct correlation between the strength of the hydrogen bond to the proximal imidazole ligand and the ground state of the complexes. With neutral imidazole coordination, the doubly occupied d-orbital of high-spin iron(II) is of d(π) character, located orthogonal to the heme plane. As the strength of the hydrogen bond increases, this orbital rotates into the heme plane, changing the ground state of the complex.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry, The University of Michigan, 930 North University Avenue, Ann Arbor, MI 48109-1055, USA.
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Application of magnetically-perturbed time-dependent density functional theory to magnetic circular dichroism. IV. The influence of zero-field splitting on the spectra of S>1/2 molecules. Chem Phys 2012. [DOI: 10.1016/j.chemphys.2011.06.016] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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25
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Bane K, Geiger RA, Chabolla SA, Jackson TA. Determination of zero-field splitting parameters for a MnIV center using variable-temperature, variable-field magnetic circular dichroism spectroscopy: Comparison to electron paramagnetic resonance spectroscopy. Inorganica Chim Acta 2012. [DOI: 10.1016/j.ica.2011.10.046] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Zhekova HR, Seth M, Ziegler T. First Principle Simulation of the Temperature Dependent Magnetic Circular Dichroism of a Trinuclear Copper Complex in the Presence of Zero Field Splitting. J Phys Chem A 2011; 115:10323-34. [DOI: 10.1021/jp203326m] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Affiliation(s)
- Hristina R. Zhekova
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
| | - Michael Seth
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
| | - Tom Ziegler
- Department of Chemistry, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada
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Ostrovsky S. Peculiarities of MCD C-term saturation behavior of the exchange coupled Co(II) dimers. Chem Phys 2011. [DOI: 10.1016/j.chemphys.2011.06.029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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McMaster J, Oganesyan VS. Magnetic circular dichroism spectroscopy as a probe of the structures of the metal sites in metalloproteins. Curr Opin Struct Biol 2010; 20:615-22. [PMID: 20619632 DOI: 10.1016/j.sbi.2010.06.006] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 06/07/2010] [Accepted: 06/09/2010] [Indexed: 11/30/2022]
Abstract
Magnetic circular dichroism (MCD) is a powerful probe of the electronic and geometric structures of metal centres in metalloproteins. MCD has provided significant insight into the nature of the axial donors at haem centres and, more recently, sophisticated methods for the analysis of MCD spectra have had a major impact on the study of the electronic structures of the ground states of a range of Cu, non-haem iron and Mo-containing active sites. This detail, together with data from other complimentary spectroscopies, has played a major role in defining the chemistry underpinning the catalysis achieved by these metal centres.
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Affiliation(s)
- Jonathan McMaster
- School of Chemistry, The University of Nottingham, Nottingham NG7 2RD, UK.
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Ostrovsky S, Tomkowicz Z, Haase W. Exchange-Coupled Cobalt(II) Dimer with Unusual Magnetic Circular Dichroism Saturation Behavior. Inorg Chem 2010; 49:6942-7. [DOI: 10.1021/ic100556p] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- S. Ostrovsky
- Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt, Germany
- Institute of Applied Physics, Academy of Sciences of Moldova, Academy 5, MD-2028 Chisinau, Moldova
| | - Z. Tomkowicz
- Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt, Germany
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland
| | - W. Haase
- Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt, Germany
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Geiger RA, Chattopadhyay S, Day VW, Jackson TA. A Series of Peroxomanganese(III) Complexes Supported by Tetradentate Aminopyridyl Ligands: Detailed Spectroscopic and Computational Studies. J Am Chem Soc 2010; 132:2821-31. [DOI: 10.1021/ja910235g] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Robert A. Geiger
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045
| | - Swarup Chattopadhyay
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045
| | - Victor W. Day
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045
| | - Timothy A. Jackson
- Department of Chemistry and Center for Environmentally Beneficial Catalysis, University of Kansas, Lawrence, Kansas 66045
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Calculation of Magnetic Circular Dichroism Spectra With Time-Dependent Density Functional Theory. ADVANCES IN INORGANIC CHEMISTRY 2010. [DOI: 10.1016/s0898-8838(10)62002-8] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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Sundararajan M, Ganyushin D, Ye S, Neese F. Multireference ab initio studies of zero-field splitting and magnetic circular dichroism spectra of tetrahedral Co(II) complexes. Dalton Trans 2009:6021-36. [PMID: 19623403 DOI: 10.1039/b902743b] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A newly developed multireference (MR) ab initio method for the calculation of magnetic circular dichroism (MCD) spectra was calibrated through the calculation of the ground- and excited state properties of seven high-spin (S = 3/2) Co(II) complexes. The MCD spectra were computed by the explicit treatment of spin-orbit coupled (SOC) and spin-spin coupled (SSC) N-electron states. For the complexes studied in this work, we found that the SOC is more important than the SSC for determining the ground state zero field splitting (ZFS). Our computed ZFS parameter D for the [Co(PPh(3))(2)Cl(2)] model complex is -17.6 cm(-1), which is reasonably close to the experimental value of -14.8 cm(-1). Generally, the computed absorption and MCD spectra are in fair agreement with experiment for all investigated complexes. Thus, reliable electronic structure and spectroscopic predictions for medium sized transition metal complexes are feasible on the basis of this methodology. This characterizes the presented method as a promising tool for MCD spectra interpretations of transition metal complexes in a variety of areas of chemistry and biology.
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Affiliation(s)
- Mahesh Sundararajan
- Institut für Physikalische und Theoretische Chemie, Wegelerstr. 12, University of Bonn, D-53115 Bonn, Germany
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Novak R, Pineider F, de Julián Fernández C, Gorini L, Bogani L, Danieli C, Cavigli L, Cornia A, Sessoli R. Magneto-optical studies on the molecular cluster Fe4 in different polymeric environments. Inorganica Chim Acta 2008. [DOI: 10.1016/j.ica.2008.03.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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35
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Seth M, Ziegler T, Autschbach J. Application of magnetically perturbed time-dependent density functional theory to magnetic circular dichroism. III. Temperature-dependent magnetic circular dichroism induced by spin-orbit coupling. J Chem Phys 2008; 129:104105. [DOI: 10.1063/1.2976568] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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36
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Tomkowicz Z, Ostrovsky S, Müller-Bunz H, Eltmimi AJH, Rams M, Brown DA, Haase W. Extended Triple-Bridged Ni(II)- and Co(II)-Hydroxamate Trinuclear Complexes: Synthesis, Crystal Structures, and Magnetic Properties. Inorg Chem 2008; 47:6956-63. [DOI: 10.1021/ic800264y] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Z. Tomkowicz
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - S. Ostrovsky
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - H. Müller-Bunz
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - A. J. Hussein Eltmimi
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - M. Rams
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - D. A. Brown
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
| | - W. Haase
- Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland, Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova, Department of Chemistry, Centre for Synthesis and Chemical Biology, Convay Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland, and Eduard-Zintl-Institute of Inorganic and Physical Chemistry, Darmstadt University of Technology, Petersenstrasse 20, 64287 Darmstadt,
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Paulat F, Lehnert N. Detailed assignment of the magnetic circular dichroism and UV-vis spectra of five-coordinate high-spin ferric [Fe(TPP)(Cl)]. Inorg Chem 2008; 47:4963-76. [PMID: 18438984 DOI: 10.1021/ic8002838] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
High-spin (hs) ferric heme centers occur in the catalytic or redox cycles of many metalloproteins and exhibit very complicated magnetic circular dichroism (MCD) and UV-vis absorption spectra. Therefore, detailed assignments of the MCD spectra of these species are missing. In this study, the electronic spectra (MCD and UV-vis) of the five-coordinate hs ferric model complex [Fe(TPP)(Cl)] are analyzed and assigned for the first time. A correlated fit of the absorption and low-temperature MCD spectra of [Fe(TPP)(Cl)] lead to the identification of at least 20 different electronic transitions. The assignments of these spectra are based on the following: (a) variable temperature and variable field saturation data, (b) time-dependent density functional theory calculations, (c) MCD pseudo A-terms, and (d) correlation to resonance Raman (rRaman) data to validate the assignments. From these results, a number of puzzling questions about the electronic spectra of [Fe(TPP)(Cl)] are answered. The Soret band in [Fe(TPP)(Cl)] is split into three components because one of its components is mixed with the porphyrin A2u72-->Eg82/83 (pi-->pi*) transition. The broad, intense absorption feature at higher energy from the Soret band is due to one of the Soret components and a mixed sigma and pi chloro to iron CT transition. The high-temperature MCD data allow for the identification of the Q v band at 20 202 cm(-1), which corresponds to the C-term feature at 20 150 cm(-1). Q is not observed but can be localized by correlation to rRaman data published before. Finally, the low energy absorption band around 650 nm is assigned to two P-->Fe charge transfer transitions, one being the long sought after A1u(HOMO)-->d pi transition.
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Affiliation(s)
- Florian Paulat
- Department of Chemistry, The University of Michigan, Ann Arbor, MI 48109-1055, USA
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38
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Grove LE, Xie J, Yikilmaz E, Miller AF, Brunold TC. Spectroscopic and computational investigation of second-sphere contributions to redox tuning in Escherichia coli iron superoxide dismutase. Inorg Chem 2008; 47:3978-92. [PMID: 18433120 DOI: 10.1021/ic702412y] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In Fe- and Mn-dependent superoxide dismutases (SODs), second-sphere residues have been implicated in precisely tuning the metal ion reduction potential to maximize catalytic activity (Vance, C. K.; Miller, A.-F. J. Am. Chem. Soc. 1998, 120, 461-467). In the present study, spectroscopic and computational methods were used to characterize three distinct Fe-bound SOD species that possess different second-coordination spheres and, consequently, Fe(3+/2+)reduction potentials that vary by approximately 1 V, namely, FeSOD, Fe-substituted MnSOD (Fe(Mn)SOD), and the Q69E FeSOD mutant. Despite having markedly different metal ion reduction potentials, FeSOD, Fe(Mn)SOD, and Q69E FeSOD exhibit virtually identical electronic absorption, circular dichroism, and magnetic circular dichroism (MCD) spectra in both their oxidized and reduced states. Likewise, variable-temperature, variable-field MCD data obtained for the oxidized and reduced species do not reveal any significant electronic, and thus geometric, variations within the Fe ligand environment. To gain insight into the mechanism of metal ion redox tuning, complete enzyme models for the oxidized and reduced states of all three Fe-bound SOD species were generated using combined quantum mechanics/molecular mechanics (QM/MM) geometry optimizations. Consistent with our spectroscopic data, density functional theory computations performed on the corresponding active-site models predict that the three SOD species share similar active-site electronic structures in both their oxidized and reduced states. By using the QM/MM-optimized active-site models in conjunction with the conductor-like screening model to calculate the proton-coupled Fe(3+/2+) reduction potentials, we found that different hydrogen-bonding interactions with the conserved second-sphere Gln (changed to Glu in Q69E FeSOD) greatly perturb the p K of the Fe-bound solvent ligand and, thus, drastically affect the proton-coupled metal ion reduction potential.
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Affiliation(s)
- Laurie E Grove
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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39
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Ganyushin D, Neese F. First-principles calculations of magnetic circular dichroism spectra. J Chem Phys 2008; 128:114117. [DOI: 10.1063/1.2894297] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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40
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Oganesyan VS, Cheesman MR, Thomson AJ. Magnetic Circular Dichroism Evidence for a Weakly Coupled Heme-Radical Pair at the Active Site of Cytochrome cd1, a Nitrite Reductase. Inorg Chem 2007; 46:10950-2. [DOI: 10.1021/ic701556y] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Vasily S. Oganesyan
- Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Myles R. Cheesman
- Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K
| | - Andrew J. Thomson
- Centre for Metalloprotein Spectroscopy and Biology, School of Chemical Sciences and Pharmacy, University of East Anglia, Norwich NR4 7TJ, U.K
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41
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Tan ML, Bizzarri AR, Xiao Y, Cannistraro S, Ichiye T, Manzoni C, Cerullo G, Adams MWW, Jenney FE, Cramer SP. Observation of terahertz vibrations in Pyrococcus furiosus rubredoxin via impulsive coherent vibrational spectroscopy and nuclear resonance vibrational spectroscopy – interpretation by molecular mechanics. J Inorg Biochem 2007; 101:375-84. [PMID: 17204331 DOI: 10.1016/j.jinorgbio.2006.09.031] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2006] [Revised: 09/28/2006] [Accepted: 09/29/2006] [Indexed: 10/24/2022]
Abstract
We have used impulsive coherent vibrational spectroscopy (ICVS) to study the Fe(S-Cys)(4) site in oxidized rubredoxin (Rd) from Pyrococcus furiosus (Pf). In this experiment, a 15 fs visible laser pulse is used to coherently pump the sample to an excited electronic state, and a second <10 fs pulse is used to probe the change in transmission as a function of the time delay. PfRd was observed to relax to the ground state by a single exponential decay with time constants of approximately 255-275 fs. Superimposed on this relaxation are oscillations caused by coherent excitation of vibrational modes in both excited and ground electronic states. Fourier transformation reveals the frequencies of these modes. The strongest ICV mode with 570 nm excitation is the symmetric Fe-S stretching mode near 310 cm(-1), compared to 313 cm(-1) in the low temperature resonance Raman. If the rubredoxin is pumped at 520 nm, a set of strong bands occurs between 20 and 110 cm(-1). Finally, there is a mode at approximately 500 cm(-1) which is similar to features near 508 cm(-1) in blue Cu proteins that have been attributed to excited state vibrations. Normal mode analysis using 488 protein atoms and 558 waters gave calculated spectra that are in good agreement with previous nuclear resonance vibrational spectra (NRVS) results. The lowest frequency normal modes are identified as collective motions of the entire protein or large segments of polypeptide. Motion in these modes may affect the polar environment of the redox site and thus tune the electron transfer functions in rubredoxins.
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Affiliation(s)
- Ming-Liang Tan
- Department of Applied Science, University of California, Davis, CA 95616, USA
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42
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Praneeth VKK, Näther C, Peters G, Lehnert N. Spectroscopic Properties and Electronic Structure of Five- and Six-Coordinate Iron(II) Porphyrin NO Complexes: Effect of the Axial N-Donor Ligand. Inorg Chem 2006; 45:2795-811. [PMID: 16562937 DOI: 10.1021/ic050865j] [Citation(s) in RCA: 147] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In this paper, the differences in the spectroscopic properties and electronic structures of five- and six-coordinate iron(II) porphyrin NO complexes are explored using [Fe(TPP)(NO)] (1; TPP = tetraphenylporphyrin) and [Fe(TPP)(MI)(NO)] (2; MI = 1-methylimidazole) type systems. Binding of N-donor ligands in axial position trans to NO to five-coordinate complexes of type 1 is investigated using UV-vis absorption and 1H NMR spectroscopies. This way, the corresponding binding constants Keq are determined and the 1H NMR spectra of 1 and 2 are assigned for the first time. In addition, 1H NMR allows for the determination of the degree of denitrosylation in solutions of 1 with excess base. The influence of the axial ligand on the properties of the coordinated NO is then investigated. Vibrational spectra (IR and Raman) of 1 and 2 are presented and assigned using isotope substitution and normal-coordinate analysis. Obtained force constants are 12.53 (N-O) and 2.98 mdyn/A (Fe-NO) for 1 compared to 11.55 (N-O) and 2.55 mdyn/A (Fe-NO) for 2. Together with the NMR results, this provides experimental evidence that binding of the trans ligand weakens the Fe-NO bond. The principal bonding schemes of 1 and 2 are very similar. In both cases, the Fe-N-O subunit is strongly bent. Donation from the singly occupied pi* orbital of NO into d(z2) of iron(II) leads to the formation of an Fe-NO sigma bond. In addition, a medium-strong pi back-bond is present in these complexes. The most important difference in the electronic structures of 1 and 2 occurs for the Fe-NO sigma bond, which is distinctively stronger for 1 in agreement with the experimental force constants. The increased sigma donation from NO in 1 also leads to a significant transfer of spin density from NO to iron, as has been shown by magnetic circular dichroism (MCD) spectroscopy in a preceding Communication (Praneeth, V. K. K.; Neese, F.; Lehnert, N. Inorg. Chem. 2005, 44, 2570-2572). This is confirmed by the 1H NMR results presented here. Hence, further experimental and computational evidence is provided that complex 1 has noticeable Fe(I)NO+ character relative to 2, which is an Fe(II)NO(radical) complex. Finally, using MCD theory and quantum chemical calculations, the absorption and MCD C-term spectra of 1 and 2 are assigned for the first time.
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Affiliation(s)
- V K K Praneeth
- Institut für Anorganische Chemie, Christian-Albrechts-Universität Kiel, Olshausenstrasse 40, D-24098 Kiel, Germany
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Ostrovsky SM, Falk K, Pelikan J, Brown DA, Tomkowicz Z, Haase W. Orbital Angular Momentum Contribution to the Magneto-Optical Behavior of a Binuclear Cobalt(II) Complex. Inorg Chem 2005; 45:688-94. [PMID: 16411704 DOI: 10.1021/ic0514748] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report magnetic and magnetic circular dichroism investigations of a binuclear Co(II) compound. The Hamiltonian of the system involves an isotropic exchange interaction dealing with the real spins of cobalt(II) ions, spin-orbit coupling, and a low-symmetry crystal field acting within the (4)T(1g) ground manifold of each cobalt ion. It is shown that spin-orbit coupling between this ground term and the low-lying excited ones can be taken into consideration as an effective g factor in the Zeeman part of the Hamiltonian. The value of this g factor is estimated for the averaged experimental values of Racah and cubic ligand field parameters for high-spin cobalt(II). The treatment of the Hamiltonian is performed with the use of a irreducible tensor operator technique. The results of the calculation are in good agreement with experimental observations. Both a large effective g factor for the ground state and a large temperature-independent part of the magnetic susceptibility arise because of a strong orbital contribution to the magnetic behavior of the Co(II) dimer.
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Affiliation(s)
- S M Ostrovsky
- Institute of Applied Physics, Academy of Sciences of Moldova, Academy str. 5, MD-2028 Chisinau, Moldova.
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Praneeth VKK, Neese F, Lehnert N. Spin Density Distribution in Five- and Six-Coordinate Iron(II)−Porphyrin NO Complexes Evidenced by Magnetic Circular Dichroism Spectroscopy. Inorg Chem 2005; 44:2570-2. [PMID: 15819537 DOI: 10.1021/ic050144k] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Using magnetic circular dichroism (MCD) spectroscopy together with DFT calculations, the spin density distributions in five-coordinate [Fe(TPP)(NO)] (I) and six-coordinate [Fe(TPP)(MI)(NO)] (II, MI = 1-methylimidazole) are defined. In the five-coordinate complex, a strong Fe-NO sigma bond between pi(*)(h) and d(z)(2) is present that leads to a large transfer of spin density from the NO ligand to Fe(II) corresponding to an electronic structure with noticeable Fe(I)-NO(+) character. Consequently, the MCD spectrum is dominated by paramagnetic C-term contributions. On coordination of the sixth ligand, the spin density is pushed back from the iron toward the NO ligand, resulting in an Fe(II)-NO(radical) type of electronic structure. This is reflected by the fact that the MCD spectrum is dominated by diamagnetic contributions.
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Affiliation(s)
- V K K Praneeth
- Institut für Anorganische Chemie, Christian-Albrechts-Universität Kiel, Olshausenstrasse 40, 24098 Kiel, Germany
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45
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Jackson TA, Karapetian A, Miller AF, Brunold TC. Probing the Geometric and Electronic Structures of the Low-Temperature Azide Adduct and the Product-Inhibited Form of Oxidized Manganese Superoxide Dismutase. Biochemistry 2005; 44:1504-20. [PMID: 15683235 DOI: 10.1021/bi048639t] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The geometric and electronic structures of the six-coordinate azide adduct of oxidized manganese superoxide dismutase (Mn3+ SOD) that is formed at low temperatures, LT N3-Mn3+ SOD, has been examined in detail through a combined spectroscopic/computational approach. Electronic absorption, circular dichroism (CD), magnetic CD (MCD) and variable-temperature, variable-field (VTVH) MCD spectroscopies were used to determine electronic transition energies and to obtain an estimate of zero-field splitting parameters for LT N3-Mn3+ SOD. These experimental data were utilized in conjunction with semiempirical intermediate neglect of differential overlap/spectroscopic parametrization-configuration interaction (INDO/S-CI) and time-dependent density functional theory (TD-DFT) computations to evaluate hypothetical active-site models of LT N3-Mn3+ SOD generated by constrained DFT geometry optimizations. Collectively, our spectroscopic/computational results indicate that N3- binding to Mn3+ SOD at low temperatures promotes neither protonation of the axial solvent ligand nor reorientation of the redox-active molecular orbital, both of which had been previously suggested. Using the same experimentally validated computational approach, models of the product-inhibited form of MnSOD were also developed and evaluated by their relative energies and TD-DFT-computed absorption spectra. On the basis of our computational results as well as previously published kinetic data, we propose that the product-inhibited form of MnSOD is best described as a side-on peroxo-Mn3+ adduct possessing an axial H2O ligand. Notably, attempts to generate a stable hydroperoxo-Mn3+ SOD species by protonation of the proximal O atom of the hydroperoxo ligand resulted in dissociation of HOO- and eventual H+ transfer from Tyr34 to HOO-, generating deprotonated Tyr34 and H2O2. The implications of these results with respect to the mechanism of O2*- dismutation by MnSOD are discussed.
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Affiliation(s)
- Timothy A Jackson
- Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA
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Cheesman MR, Oganesyan VS, Watmough NJ, Butler CS, Thomson AJ. The nature of the exchange coupling between high-spin Fe(III) heme o3 and CuBII in Escherichia coli quinol oxidase, cytochrome bo3: MCD and EPR studies. J Am Chem Soc 2004; 126:4157-66. [PMID: 15053605 DOI: 10.1021/ja038858m] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Fully oxidized cytochrome bo3 from Escherichia coli has been studied in its oxidized and several ligand-bound forms using electron paramagnetic resonance (EPR) and magnetic circular dichroism (MCD) spectroscopies. In each form, the spin-coupled high-spin Fe(III) heme o3 and CuB(II) ion at the active site give rise to similar fast-relaxing broad features in the dual-mode X-band EPR spectra. Simulations of dual-mode spectra are presented which show that this EPR can arise only from a dinuclear site in which the metal ions are weakly coupled by an anisotropic exchange interaction of J 1 cm-1. A variable-temperature and magnetic field (VTVF) MCD study is also presented for the cytochrome bo3 fluoride and azide derivatives. New methods are used to extract the contribution to the MCD of the spin-coupled active site in the presence of strong transitions from low-spin Fe(III) heme b. Analysis of the MCD data, independent of the EPR study, also shows that the spin-coupling within the active site is weak with J approximately 1 cm-1. These conclusions overturn a long-held view that such EPR signals in bovine cytochrome c oxidase arise from an S' = 2 ground state resulting from strong exchange coupling (J > 10(2) cm-1) within the active site.
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Affiliation(s)
- Myles R Cheesman
- School of Chemical Sciences and Pharmacy, Centre for Metalloprotein Spectroscopy and Biology (CMSB), University of East Anglia, Norwich NR4 7TJ, U.K.
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47
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Jackson TA, Yikilmaz E, Miller AF, Brunold TC. Spectroscopic and computational study of a non-heme iron [Fe-NO]7 system: exploring the geometric and electronic structures of the nitrosyl adduct of iron superoxide dismutase. J Am Chem Soc 2003; 125:8348-63. [PMID: 12837107 DOI: 10.1021/ja029523s] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Like many non-heme iron enzymes, reduced iron superoxide dismutase (Fe(2+)SOD) reacts with nitric oxide (NO) to yield an [Fe-NO]7 system. Electron paramagnetic resonance (EPR) data obtained for this Fe-NO adduct of FeSOD (NO-FeSOD) exhibit two rhombic S = 3/2 signals of comparable population; E/D = 0.128 (42%) and 0.154 (58%). While similar results were previously reported for NO-FeSOD [Niederhoffer, E. C.; Fee, J. A.; Papaefthymiou, V.; Münck, E. Magnetic Resonance Studies Involving Iron Superoxide Dismutase from Escherichia coli. Isotope and Nuclear Chemistry Division Annual Report; Los Alamos National Laboratory: Los Alamos, NM, 1987], detailed geometric and electronic structure descriptions of these [Fe-NO]7 systems had not yet been developed. Therefore, in addition to EPR spectroscopy, we have used electronic absorption, magnetic circular dichroism (MCD), variable-temperature, variable-field MCD, and resonance Raman spectroscopies to determine ground-state spin Hamiltonian parameters, electronic transition energies, oscillator strengths, and transition polarizations for NO-FeSOD. These spectroscopic parameters have been used in conjunction with density functional theory (DFT) and semiempirical INDO/S-CI calculations to generate an experimentally calibrated active site model for NO-FeSOD. Our studies indicate that NO binds to the active site of Fe(2+)SOD to form a six-coordinate [Fe-NO]7 system with an Fe-N-O angle of approximately 145 degrees. DFT computations performed on this model of NO-FeSOD reveal that the NO ligand is formally reduced by the ferrous center to yield NO(-) and an Fe(3+) center that are strongly antiferromagnetically coupled. DFT calculations reveal that NO binding to Fe(2+)SOD also lowers the pK of the coordinated water ligand by at least 3.3 pH units, suggesting that this process is associated with increased acidity and probable ionization of the axial solvent ligand. To explore the origin of the two [Fe-NO]7 systems observed by EPR spectroscopy, additional calculations have been performed on slightly perturbed NO-FeSOD models. Significantly, semiempirical INDO/S-CI computations reveal that the rhombicity of NO-FeSOD is altered by changes in the Fe-N-O angle or rotation about the Fe-N(O) bond, suggesting that the two species observed by EPR spectroscopy merely differ slightly with respect to the orientation of the NO ligand. Indeed, our EPR data obtained on NO-FeSOD variants indicate that the relative population of the S = 3/2 signals can be altered by perturbations in the second sphere of the protein active site. These results provide compelling evidence that the second coordination sphere is able to modulate the geometric and electronic structures of NO-FeSOD.
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Affiliation(s)
- Timothy A Jackson
- Department of Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA
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Clay MD, Emerson JP, Coulter ED, Kurtz DM, Johnson MK. Spectroscopic characterization of the [Fe(His)(4)(Cys)] site in 2Fe-superoxide reductase from Desulfovibrio vulgaris. J Biol Inorg Chem 2003; 8:671-82. [PMID: 12764688 DOI: 10.1007/s00775-003-0465-4] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2003] [Accepted: 04/11/2003] [Indexed: 10/26/2022]
Abstract
The electronic and vibrational properties of the [Fe(His)(4)(Cys)] site (Center II) responsible for catalysis of superoxide reduction in the two-iron superoxide reductase (2Fe-SOR) from Desulfovibrio vulgaris have been investigated using the combination of EPR, resonance Raman, UV/visible/near-IR absorption, CD, and VTMCD spectroscopies. Deconvolution of the spectral contributions of Center II from those of the [Fe(Cys)(4)] site (Center I) has been achieved by parallel investigations of the C13S variant, which does not contain Center I. The resonance Raman spectrum of ferric Center II has been assigned based on isotope shifts for (34)S and (15)N globally labeled proteins. As for the [Fe(His)(4)(Cys)] active site in 1Fe-SOR from Pyrococcus furiosus, the spectroscopic properties of ferric and ferrous Center II in D. vulgaris 2Fe-SOR are indicative of distorted octahedral and square-pyramidal coordination geometries, respectively. Differences in the properties of the ferric [Fe(His)(4)(Cys)] sites in 1Fe- and 2Fe-SORs are apparent in the rhombicity of the S=5/2 ground state ( E/ D=0.06 and 0.28 in 1Fe- and 2Fe-SORs, respectively), the energy of the CysS(-)(p(pi))-->Fe(3+)(d(pi)) CT transition (15150+/-150 cm(-1) and 15600+/-150 cm(-1) in 1Fe- and 2Fe-SORs, respectively) and in changes in the Fe-S stretching region of the resonance Raman spectrum indicative of a weaker Fe-S(Cys) bond in 2Fe-SORs. These differences are interpreted in terms of small structural perturbations in the Fe coordination sphere with changes in the Fe-S(Cys) bond strength resulting from differences in the peptide N-H.S(Cys) hydrogen bonding within a tetrapeptide bidentate "chelate". Observation of the characteristic intervalence charge transfer transition of a cyano-bridged [Fe(III)-NC-Fe(II)(CN)(5)] unit in the near-IR VTMCD spectra of ferricyanide-oxidized samples of both P. furiosus 1Fe-SOR and D. vulgaris 2Fe-SOR has confirmed the existence of novel ferrocyanide adducts of the ferric [Fe(His)(4)(Cys)] sites in both 1Fe- and 2Fe-SORs.
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Affiliation(s)
- Michael D Clay
- Department of Chemistry and Center for Metalloenzyme Studies, University of Georgia, Athens, GA 30602, USA
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Craft JL, Mandimutsira BS, Fujita K, Riordan CG, Brunold TC. Spectroscopic and computational studies of a Ni(+)-CO model complex: implications for the acetyl-CoA synthase catalytic mechanism. Inorg Chem 2003; 42:859-67. [PMID: 12562200 DOI: 10.1021/ic020441e] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The four-coordinate Ni(+) complex [PhTt(t)(Bu)]Ni(I)CO, where PhTt(t)()(Bu) = phenyltris((tert-buthylthio)methyl)borate (a tridentate thioether donor ligand), serves as a possible model for key Ni-CO reaction intermediates in the acetyl-CoA synthase (ACS) catalytic cycle. Resonance Raman, electronic absorption, magnetic circular dichroism (MCD), variable-temperature variable-field MCD, and electron paramagnetic resonance spectroscopies were utilized in conjunction with density functional theory and semiemperical INDO/S-CI calculations to investigate the ground and excited states of [PhTt(t)()(Bu)]Ni(I)CO. These studies reveal extensive Ni(+) --> CO pi-back-bonding interactions, as evidenced by a low C-O stretching frequency (1995 cm(-)(1)), a calculated C-O stretching force constant of 15.5 mdyn/A (as compared to k(CO)(free CO) = 18.7 mdyn/A), and strong Ni(+) --> CO charge-transfer absorption intensities. Calculations reveal that this high degree of pi-back-bonding is due to the fact that the Ni(+) 3d orbitals are in close energetic proximity to the CO pi acceptor orbitals. In the ACS "paramagnetic catalytic cycle", the high degree of pi-back-bonding in the putative Ni(+)-CO intermediate (the NiFeC species) is not expected to preclude methyl transfer from CH(3)-CoFeSP.
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Affiliation(s)
- Jennifer L Craft
- Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, USA
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