1
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Zhu W, Wu P, Larson VA, Kumar A, Li XX, Seo MS, Lee YM, Wang B, Lehnert N, Nam W. Electronic Structure and Reactivity of Mononuclear Nonheme Iron-Peroxo Complexes as a Biomimetic Model of Rieske Oxygenases: Ring Size Effects of Macrocyclic Ligands. J Am Chem Soc 2024; 146:250-262. [PMID: 38147793 DOI: 10.1021/jacs.3c08559] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
We report the macrocyclic ring size-electronic structure-electrophilic reactivity correlation of mononuclear nonheme iron(III)-peroxo complexes bearing N-tetramethylated cyclam analogues (n-TMC), [FeIII(O2)(12-TMC)]+ (1), [FeIII(O2)(13-TMC)]+ (2), and [FeIII(O2)(14-TMC)]+ (3), as a model study of Rieske oxygenases. The Fe(III)-peroxo complexes show the same δ and pseudo-σ bonds between iron and the peroxo ligand. However, the strength of these interactions varies depending on the ring size of the n-TMC ligands; the overall Fe-O bond strength and the strength of the Fe-O2 δ bond increase gradually as the ring size of the n-TMC ligands becomes smaller, such as from 14-TMC to 13-TMC to 12-TMC. MCD spectroscopy plays a key role in assigning the characteristic low-energy δ → δ* LMCT band, which provides direct insight into the strength of the Fe-O2 δ bond and which, in turn, is correlated with the superoxo character of the iron-peroxo group. In oxidation reactions, reactivities of 1-3 toward hydrocarbon C-H bond activation are compared, revealing the reactivity order of 1 > 2 > 3; the [FeIII(O2)(n-TMC)]+ complex with a smaller n-TMC ring size, 12-TMC, is much more reactive than that with a larger n-TMC ring size, 14-TMC. DFT analysis shows that the Fe(III)-peroxo complex is not reactive toward C-H bonds, but it is the end-on Fe(II)-superoxo valence tautomer that is responsible for the observed reactivity. The hydrogen atom abstraction (HAA) reactivity of these intermediates is correlated with the overall donicity of the n-TMC ligand, which modulates the energy of the singly occupied π* superoxo frontier orbital that serves as the electron acceptor in the HAA reaction. The implications of these results for the mechanism of Rieske oxygenases are further discussed.
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Affiliation(s)
- Wenjuan Zhu
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Peng Wu
- State Key Laboratory of High-Efficiency Utilization of Coal and Green Chemical Engineering, School of Chemistry and Chemical Engineering, Ningxia University, Yinchuan 750021, P. R. China
| | - Virginia A Larson
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Akhilesh Kumar
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Xiao-Xi Li
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
- Institute of Molecular Sciences and Engineering, Institute of Frontier and Interdisciplinary Science, Shandong University, Qingdao 266237, P. R. China
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Binju Wang
- Key Laboratory of Physical Chemistry of Solid Surfaces and Fujian Provincial Key Laboratory of Theoretical and Computational Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, P. R. China
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
- College of Chemistry and Chemical Engineering, Yan'an University, Yan'an, Shaanxi Province 716000, P. R. China
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2
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Karmalkar DG, Larson VA, Malik DD, Lee YM, Seo MS, Kim J, Vasiliauskas D, Shearer J, Lehnert N, Nam W. Preparation and Characterization of a Formally Ni IV-Oxo Complex with a Triplet Ground State and Application in Oxidation Reactions. J Am Chem Soc 2022; 144:22698-22712. [PMID: 36454200 DOI: 10.1021/jacs.2c10196] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
High-valent first-row transition-metal-oxo complexes are important intermediates in biologically and chemically relevant oxidative transformations of organic molecules and in the water splitting reaction in (artificial) photosynthesis. While high-valent Fe- and Mn-oxo complexes have been characterized in detail, much less is known about their analogues with late transition metals. In this study, we present the synthesis and detailed characterization of a unique mononuclear terminal Ni-O complex. This compound, [Ni(TAML)(O)(OH)]3-, is characterized by an intense charge-transfer (CT) band around 730 nm and has an St = 1 ground state, as determined by magnetic circular dichroism spectroscopy. From extended X-ray absorption fine structure (EXAFS), the Ni-O bond distance is 1.84 Å. Ni K edge XAS data indicate that the complex contains a Ni(III) center, which results from an unusually large degree of Ni-O π-bond inversion, with one hole located on the oxo ligand. The complex is therefore best described as a low-spin Ni(III) complex (S = 1/2) with a bound oxyl (O•-) ligand (S = 1/2), where the spins of Ni and oxyl are ferromagnetically coupled, giving rise to the observed St = 1 ground state. This bonding description is roughly equivalent to the presence of a Ni-O single (σ) bond. Reactivity studies show that [Ni(TAML)(O)(OH)]3- is a strong oxidant capable of oxidizing thioanisole and styrene derivatives with large negative ρ values in the Hammett plot, indicating its electrophilic nature. The intermediate also shows high reactivity in C-H bond activation of hydrocarbons with a kinetic isotope effect of 7.0(3) in xanthene oxidation.
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Affiliation(s)
- Deepika G Karmalkar
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Virginia A Larson
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Deesha D Malik
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Jin Kim
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Dovydas Vasiliauskas
- Department of Chemistry, Trinity University, San Antonio, Texas 78212-7200, United States
| | - Jason Shearer
- Department of Chemistry, Trinity University, San Antonio, Texas 78212-7200, United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
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3
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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: 96] [Impact Index Per Article: 32.0] [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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4
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Yang J, Dong HT, Seo MS, Larson VA, Lee YM, Shearer J, Lehnert N, Nam W. The Oxo-Wall Remains Intact: A Tetrahedrally Distorted Co(IV)-Oxo Complex. J Am Chem Soc 2021; 143:16943-16959. [PMID: 34609879 DOI: 10.1021/jacs.1c04919] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In this paper, we report the preparation, spectroscopic and theoretical characterization, and reactivity studies of a Co(IV)-oxo complex bearing an N4-macrocyclic coligand, 12-TBC (12-TBC = 1,4,7,10-tetrabenzyl-1,4,7,10-tetraazacyclododecane). On the basis of the ligand and the structure of the Co(II) precursor, [CoII(12-TBC)(CF3SO3)2], one would assume that this species corresponds to a tetragonal Co(IV)-oxo complex, but the spectroscopic data do not support this notion. Co K-edge XAS data show that the treatment of the Co(II) precursor with iodosylbenzene (PhIO) as an oxidant at -40 °C in the presence of a proton source leads to a distinct shift in the Co K-edge, in agreement with the formation of a Co(IV) intermediate. The presence of the oxo group is further demonstrated by resonance Raman (rRaman) spectroscopy. Interestingly, the EPR data of this complex show a high degree of rhombicity, indicating structural distortion. This is further supported by the EXAFS data. Using DFT calculations, a structural model is developed for this complex with a ligand-protonated structure that features a Co═O···HN hydrogen bond and a four-coordinate Co center in a seesaw-shaped coordination geometry. Magnetic circular dichroism (MCD) spectroscopy further supports this finding. The hydrogen bond leads to an interesting polarization of the Co-oxo π-bonds, where one O(p) lone-pair is stabilized and leads to a regular Co(d) interaction, whereas the other π-bond shows an inverted ligand field. The reactivity of this complex in hydrogen atom and oxygen atom transfer reactions is discussed as well.
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Affiliation(s)
- Jindou Yang
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Hai T Dong
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Mi Sook Seo
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Virginia A Larson
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Yong-Min Lee
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea
| | - Jason Shearer
- Department of Chemistry, Trinity University, San Antonio, Texas 78212-7200, United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Wonwoo Nam
- Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.,School of Chemistry and Chemical Engineering, University of Jinan, Jinan 250022, China
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5
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Galinato MGI, Brocious EP, Paulat F, Martin S, Skodack J, Harland JB, Lehnert N. Elucidating the Electronic Structure of High-Spin [MnIII(TPP)Cl] Using Magnetic Circular Dichroism Spectroscopy. Inorg Chem 2020; 59:2144-2162. [DOI: 10.1021/acs.inorgchem.9b02599] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Mary Grace I. Galinato
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
- School of Science-Chemistry, Penn State Behrend, Erie, Pennsylvania 16563, United States
| | - Emily P. Brocious
- School of Science-Chemistry, Penn State Behrend, Erie, Pennsylvania 16563, United States
| | - Florian Paulat
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Sherri Martin
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Joshua Skodack
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Jill B. Harland
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109-1055, United States
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6
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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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7
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McQuarters AB, Blaesi EJ, Kampf JW, Alp EE, Zhao J, Hu M, Krebs C, Lehnert N. Synthetic Model Complex of the Key Intermediate in Cytochrome P450 Nitric Oxide Reductase. Inorg Chem 2019; 58:1398-1413. [PMID: 30623648 DOI: 10.1021/acs.inorgchem.8b02947] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Fungal denitrification plays a crucial role in the nitrogen cycle and contributes to the total N2O emission from agricultural soils. Here, cytochrome P450 NO reductase (P450nor) reduces two NO to N2O using a single heme site. Despite much research, the exact nature of the critical "Intermediate I" responsible for the key N-N coupling step in P450nor is unknown. This species likely corresponds to a Fe-NHOH-type intermediate with an unknown electronic structure. Here we report a new strategy to generate a model system for this intermediate, starting from the iron(III) methylhydroxylamide complex [Fe(3,5-Me-BAFP)(NHOMe)] (1), which was fully characterized by 1H NMR, UV-vis, electron paramagnetic resonance, and vibrational spectroscopy (rRaman and NRVS). Our data show that 1 is a high-spin ferric complex with an N-bound hydroxylamide ligand that is strongly coordinated (Fe-N distance, 1.918 Å; Fe-NHOMe stretch, 558 cm-1). Simple one-electron oxidation of 1 at -80 °C then cleanly generates the first model system for Intermediate I, [Fe(3,5-Me-BAFP)(NHOMe)]+ (1+). UV-vis, resonance Raman, and Mössbauer spectroscopies, in comparison to the chloro analogue [Fe(3,5-Me-BAFP)(Cl)]+, demonstrate that 1+ is best described as an FeIII-(NHOMe)• complex with a bound NHOMe radical. Further reactivity studies show that 1+ is highly reactive toward NO, a reaction that likely proceeds via N-N bond formation, following a radical-radical-type coupling mechanism. Our results therefore provide experimental evidence, for the first time, that an FeIII-(NHOMe)• electronic structure is indeed a reasonable electronic description for Intermediate I and that this electronic structure is advantageous for P450nor catalysis because it can greatly facilitate N-N bond formation and, ultimately, N2O generation.
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Affiliation(s)
- Ashley B McQuarters
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - Elizabeth J Blaesi
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Jeff W Kampf
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
| | - E Ercan Alp
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Jiyong Zhao
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Michael Hu
- Advanced Photon Source (APS) , Argonne National Laboratory (ANL) , Argonne , Illinois 60439 , United States
| | - Carsten Krebs
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109 , United States
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8
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Speelman AL, White CJ, Zhang B, Alp EE, Zhao J, Hu M, Krebs C, Penner-Hahn J, Lehnert N. Non-heme High-Spin {FeNO} 6-8 Complexes: One Ligand Platform Can Do It All. J Am Chem Soc 2018; 140:11341-11359. [PMID: 30107126 DOI: 10.1021/jacs.8b06095] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Heme and non-heme iron-nitrosyl complexes are important intermediates in biology. While there are numerous examples of low-spin heme iron-nitrosyl complexes in different oxidation states, much less is known about high-spin (hs) non-heme iron-nitrosyls in oxidation states other than the formally ferrous NO adducts ({FeNO}7 in the Enemark-Feltham notation). In this study, we present a complete series of hs-{FeNO}6-8 complexes using the TMG3tren coligand. Redox transformations from the hs-{FeNO}7 complex [Fe(TMG3tren)(NO)]2+ to its {FeNO}6 and {FeNO}8 analogs do not alter the coordination environment of the iron center, allowing for detailed comparisons between these species. Here, we present new MCD, NRVS, XANES/EXAFS, and Mössbauer data, demonstrating that these redox transformations are metal based, which allows us to access hs-Fe(II)-NO-, Fe(III)-NO-, and Fe(IV)-NO- complexes. Vibrational data, analyzed by NCA, directly quantify changes in Fe-NO bonding along this series. Optical data allow for the identification of a "spectator" charge-transfer transition that, together with Mössbauer and XAS data, directly monitors the electronic changes of the Fe center. Using EXAFS, we are also able to provide structural data for all complexes. The magnetic properties of the complexes are further analyzed (from magnetic Mössbauer). The properties of our hs-{FeNO}6-8 complexes are then contrasted to corresponding, low-spin iron-nitrosyl complexes where redox transformations are generally NO centered. The hs-{FeNO}8 complex can further be protonated by weak acids, and the product of this reaction is characterized. Taken together, these results provide unprecedented insight into the properties of biologically relevant non-heme iron-nitrosyl complexes in three relevant oxidation states.
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Affiliation(s)
- Amy L Speelman
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109-1055 , United States
| | - Corey J White
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109-1055 , United States
| | - Bo Zhang
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - E Ercan Alp
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - Jiyong Zhao
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - Michael Hu
- Advanced Photon Source , Argonne National Laboratory , Argonne , Illinois 60439 , United States
| | - Carsten Krebs
- Department of Chemistry and Department of Biochemistry and Molecular Biology , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| | - James Penner-Hahn
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109-1055 , United States
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics , University of Michigan , Ann Arbor , Michigan 48109-1055 , United States
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9
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Monte-Pérez I, Kundu S, Chandra A, Craigo KE, Chernev P, Kuhlmann U, Dau H, Hildebrandt P, Greco C, Van Stappen C, Lehnert N, Ray K. Temperature Dependence of the Catalytic Two- versus Four-Electron Reduction of Dioxygen by a Hexanuclear Cobalt Complex. J Am Chem Soc 2017; 139:15033-15042. [DOI: 10.1021/jacs.7b07127] [Citation(s) in RCA: 31] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Affiliation(s)
- Inés Monte-Pérez
- Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, D-12489 Berlin, Germany
| | - Subrata Kundu
- Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, D-12489 Berlin, Germany
| | - Anirban Chandra
- Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, D-12489 Berlin, Germany
| | - Kathryn E. Craigo
- Department
of Chemistry, The University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109, United States
| | - Petko Chernev
- Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany
| | - Uwe Kuhlmann
- Department
of Chemistry, Technische Universität Berlin, Straße des
17. Juni 135, 10623 Berlin, Germany
| | - Holger Dau
- Freie Universität Berlin, FB Physik, Arnimallee 14, D-14195 Berlin, Germany
| | - Peter Hildebrandt
- Department
of Chemistry, Technische Universität Berlin, Straße des
17. Juni 135, 10623 Berlin, Germany
| | - Claudio Greco
- Department
of Earth and Environmental Sciences, University of Milano-Bicocca, Piazza
della Scienza, 1, 20126 Milan, Italy
| | - Casey Van Stappen
- Department
of Chemistry, The University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109, United States
| | - Nicolai Lehnert
- Department
of Chemistry, The University of Michigan, 930 N. University Ave., Ann Arbor, Michigan 48109, United States
| | - Kallol Ray
- Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Straße 2, D-12489 Berlin, Germany
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10
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Schuth N, Mebs S, Huwald D, Wrzolek P, Schwalbe M, Hemschemeier A, Haumann M. Effective intermediate-spin iron in O 2-transporting heme proteins. Proc Natl Acad Sci U S A 2017; 114:8556-8561. [PMID: 28739893 PMCID: PMC5559043 DOI: 10.1073/pnas.1706527114] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Proteins carrying an iron-porphyrin (heme) cofactor are essential for biological O2 management. The nature of Fe-O2 bonding in hemoproteins is debated for decades. We used energy-sampling and rapid-scan X-ray Kβ emission and K-edge absorption spectroscopy as well as quantum chemistry to determine molecular and electronic structures of unligated (deoxy), CO-inhibited (carboxy), and O2-bound (oxy) hemes in myoglobin (MB) and hemoglobin (HB) solutions and in porphyrin compounds at 20-260 K. Similar metrical and spectral features revealed analogous heme sites in MB and HB and the absence of low-spin (LS) to high-spin (HS) conversion. Amplitudes of Kβ main-line emission spectra were directly related to the formal unpaired Fe(d) spin count, indicating HS Fe(II) in deoxy and LS Fe(II) in carboxy. For oxy, two unpaired Fe(d) spins and, thus by definition, an intermediate-spin iron center, were revealed by our static and kinetic X-ray data, as supported by (time-dependent) density functional theory and complete-active-space self-consistent-field calculations. The emerging Fe-O2 bonding situation includes in essence a ferrous iron center, minor superoxide character of the noninnocent ligand, significant double-bond properties of the interaction, and three-center electron delocalization as in ozone. It resolves the apparently contradictory classical models of Pauling, Weiss, and McClure/Goddard into a unifying view of O2 bonding, tuned toward reversible oxygen transport.
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Affiliation(s)
- Nils Schuth
- Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany
| | - Stefan Mebs
- Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany
| | - Dennis Huwald
- Department of Plant Biochemistry, Section of Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Pierre Wrzolek
- Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
| | - Matthias Schwalbe
- Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany
| | - Anja Hemschemeier
- Department of Plant Biochemistry, Section of Photobiotechnology, Ruhr-Universität Bochum, 44801 Bochum, Germany
| | - Michael Haumann
- Department of Physics, Freie Universität Berlin, 14195 Berlin, Germany;
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11
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Fujisawa K, Soma S, Kurihara H, Dong HT, Bilodeau M, Lehnert N. A cobalt–nitrosyl complex with a hindered hydrotris(pyrazolyl)borate coligand: detailed electronic structure, and reactivity towards dioxygen. Dalton Trans 2017; 46:13273-13289. [DOI: 10.1039/c7dt01565h] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
The cobalt–nitrosyl complex [Co(NO)(L3)] is supported by a highly hindered tridentate nitrogen ligand, hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate (denoted as L3−), and shows a linear Co–N–O unit.
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Affiliation(s)
| | - Shoko Soma
- Department of Chemistry
- Ibaraki University
- Mito 310-8512
- Japan
| | | | - Hai T. Dong
- Department of Chemistry and Department of Biophysics
- University of Michigan
- Ann Arbor
- USA
| | - Max Bilodeau
- Department of Chemistry and Department of Biophysics
- University of Michigan
- Ann Arbor
- USA
| | - Nicolai Lehnert
- Department of Chemistry and Department of Biophysics
- University of Michigan
- Ann Arbor
- USA
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12
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McQuarters AB, Speelman AL, Chen L, Elmore BO, Fan W, Feng C, Lehnert N. Exploring second coordination sphere effects in nitric oxide synthase. J Biol Inorg Chem 2016; 21:997-1008. [PMID: 27686338 DOI: 10.1007/s00775-016-1396-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Accepted: 09/15/2016] [Indexed: 11/28/2022]
Abstract
Second coordination sphere (SCS) effects in proteins are modulated by active site residues and include hydrogen bonding, electrostatic/dipole interactions, steric interactions, and π-stacking of aromatic residues. In Cyt P450s, extended H-bonding networks are located around the proximal cysteinate ligand of the heme, referred to as the 'Cys pocket'. These hydrogen bonding networks are generally believed to regulate the Fe-S interaction. Previous work identified the S(Cys) → Fe σ CT transition in the high-spin (hs) ferric form of Cyt P450cam and corresponding Cys pocket mutants by low-temperature (LT) MCD spectroscopy [Biochemistry 50:1053, 2011]. In this work, we have investigated the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in the hs ferric state (with H4B and L-Arg bound) of rat neuronal nitric oxide synthase oxygenase construct (nNOSoxy) using MCD spectroscopy. For this purpose, wt enzyme and W409 mutants were investigated where the H-bonding network with the axial Cys ligand is perturbed. Overall, the results are similar to Cyt P450cam and show the intense S(Cys) → Fe σ CT band in the LT MCD spectrum at about 27,800 cm-1, indicating that this feature is a hallmark of {heme-thiolate} active sites. The discovery of this MCD feature could constitute a new approach to classify {heme-thiolate} sites in hs ferric proteins. Finally, the W409 mutants show that the hydrogen bond from this group only has a small effect on the Fe-S(Cys) bond strength, at least in the hs ferric form of the protein studied here. Low-temperature MCD spectroscopy is used to investigate the effect of the hydrogen bond from W409 to the axial Cys ligand of the heme in neuronal nitric oxide synthase. The intense S(Cys) → Fe σ-CT band is monitored to identify changes in the Fe-S(Cys) bond in wild-type protein and W409 mutants.
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Affiliation(s)
- Ashley B McQuarters
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Amy L Speelman
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA.,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA
| | - Li Chen
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Bradley O Elmore
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Weihong Fan
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Changjian Feng
- College of Pharmacy, University of New Mexico, Albuquerque, NM, 87131, USA
| | - Nicolai Lehnert
- Department of Chemistry, University of Michigan, Ann Arbor, MI, 48109, USA. .,Department of Biophysics, University of Michigan, Ann Arbor, MI, 48109, USA.
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13
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14
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Berto TC, Xu N, Lee SR, McNeil AJ, Alp EE, Zhao J, Richter-Addo GB, Lehnert N. Characterization of the Bridged Hyponitrite Complex {[Fe(OEP)]2(μ-N2O2)}: Reactivity of Hyponitrite Complexes and Biological Relevance. Inorg Chem 2014; 53:6398-414. [DOI: 10.1021/ic5002573] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Timothy C. Berto
- Department
of Chemistry and Department of Biophysics, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109, United States
| | - Nan Xu
- Department
of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson
Parkway, Norman, Oklahoma 73019, United States
| | - Se Ryeon Lee
- Department
of Chemistry and Department of Biophysics, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109, United States
| | - Anne J. McNeil
- Department
of Chemistry and Department of Biophysics, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109, United States
| | - E. Ercan Alp
- Argonne National Laboratory, APS/XFD, 431/D003, Argonne, Illinois 60439, United States
| | - Jiyong Zhao
- Argonne National Laboratory, APS/XFD, 431/D003, Argonne, Illinois 60439, United States
| | - George B. Richter-Addo
- Department
of Chemistry and Biochemistry, University of Oklahoma, 101 Stephenson
Parkway, Norman, Oklahoma 73019, United States
| | - Nicolai Lehnert
- Department
of Chemistry and Department of Biophysics, University of Michigan, 930 N. University Avenue, Ann Arbor, Michigan 48109, United States
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15
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Berto TC, Speelman AL, Zheng S, Lehnert N. Mono- and dinuclear non-heme iron–nitrosyl complexes: Models for key intermediates in bacterial nitric oxide reductases. Coord Chem Rev 2013. [DOI: 10.1016/j.ccr.2012.05.007] [Citation(s) in RCA: 144] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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16
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Kammler L, van Gastel M. Electronic structure of the lowest triplet state of flavin mononucleotide. J Phys Chem A 2012; 116:10090-8. [PMID: 22998491 DOI: 10.1021/jp305778v] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The electronic structure of flavin mononucleotide (FMN), an organic cofactor that plays a role in many important enzymatic reactions, has been investigated by electron paramagnetic resonance (EPR) spectroscopy, optical spectroscopy, and quantum chemistry. In particular, the triplet state of FMN, which is paramagnetic (total spin S = 1), allows an investigation of the zero field splitting parameters D and E, which are directly related to the two singly occupied molecular orbitals. Triplet EPR spectra and optical absorption spectra at different pH values in combination with time dependent density functional theory (TDDFT) reveal that the highest occupied orbital (HOMO) and lowest unoccupied orbital (LUMO) of FMN are largely unaffected by changes in the protonation state of FMN. Rather, the orbital structure of the lower lying doubly occupied orbitals changes dramatically. Additional EPR experiments have been carried out in the presence of AgNO(3), which allows the formation of an Ag-FMN triplet state with different zero field splitting parameters and population and depopulation rates. Addition of AgNO(3) only induces small changes in the optical spectrum, indicating that the Ag(+) ion only contributes to the zero field splitting by second order spin-orbit coupling and leaves the orbital structure unaffected. By a combination of the three employed methods, the observed bands in the UV/vis spectra of FMN at different pH values are assigned to electronic transitions.
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Affiliation(s)
- Lydia Kammler
- Institut für Physikalische und Theoretische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Wegelerstrasse 12, 53115, Bonn, Germany
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17
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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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18
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Galinato MGI, Spolitak T, Ballou DP, Lehnert N. Elucidating the role of the proximal cysteine hydrogen-bonding network in ferric cytochrome P450cam and corresponding mutants using magnetic circular dichroism spectroscopy. Biochemistry 2011; 50:1053-69. [PMID: 21158478 DOI: 10.1021/bi101911y] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Although extensive research has been performed on various cytochrome P450s, especially Cyt P450cam, there is much to be learned about the mechanism of how its functional unit, a heme b ligated by an axial cysteine, is finely tuned for catalysis by its second coordination sphere. Here we study how the hydrogen-bonding network affects the proximal cysteine and the Fe-S(Cys) bond in ferric Cyt P450cam. This is accomplished using low-temperature magnetic circular dichroism (MCD) spectroscopy on wild-type (wt) Cyt P450cam and on the mutants Q360P (pure ferric high-spin at low temperature) and L358P where the "Cys pocket" has been altered (by removing amino acids involved in the hydrogen-bonding network), and Y96W (pure ferric low-spin). The MCD spectrum of Q360P reveals fourteen electronic transitions between 15200 and 31050 cm(-1). Variable-temperature variable-field (VTVH) saturation curves were used to determine the polarizations of these electronic transitions with respect to in-plane (xy) and out-of-plane (z) polarization relative to the heme. The polarizations, oscillator strengths, and TD-DFT calculations were then used to assign the observed electronic transitions. In the lower energy region, prominent bands at 15909 and 16919 cm(-1) correspond to porphyrin (P) → Fe charge transfer (CT) transitions. The band at 17881 cm(-1) has distinct sulfur S(π) → Fe CT contributions. The Q band is observed as a pseudo A-term (derivative shape) at 18604 and 19539 cm(-1). In the case of the Soret band, the negative component of the expected pseudo A-term is split into two features due to mixing with another π → π* and potentially a P → Fe CT excited state. The resulting three features are observed at 23731, 24859, and 25618 cm(-1). Most importantly, the broad, prominent band at 28570 cm(-1) is assigned to the S(σ) → Fe CT transition, whose intensity is generated through a multitude of CT transitions with strong iron character. For wt, Q360P, and L358P, this band occurs at 28724, 28570, and 28620 cm(-1), respectively. The small shift of this feature upon altering the hydrogen bonds to the proximal cysteine indicates that the role of the Cys pocket is not primarily for electronic fine-tuning of the sulfur donor strength but is more for stabilizing the proximal thiolate against external reactants (NO, O(2), H(3)O(+)), and for properly positioning cysteine to coordinate to the iron center. This aspect is discussed in detail.
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Affiliation(s)
- Mary Grace I Galinato
- Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, United States
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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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20
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Hernandez-Marin E, Seth M, Ziegler T. Density Functional Theory Study of the Magnetic Circular Dichroism Spectra of Molybdenyl Complexes. Inorg Chem 2010; 49:6066-76. [DOI: 10.1021/ic100624q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
| | - Michael Seth
- Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada
| | - Tom Ziegler
- Department of Chemistry, University of Calgary, Calgary, Alberta T2N 1N4, Canada
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21
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Hernandez-Marin E, Seth M, Ziegler T. A Theoretical Study of the Magnetic Circular Dichroism Spectrum for Sulfite Oxidase Based on Time-Dependent Density Functional Theory. Inorg Chem 2009; 48:2880-6. [DOI: 10.1021/ic801875u] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
| | - Michael Seth
- Department of Chemistry, University of Calgary, Calgary, Alberta, Canada, T2N 1N4
| | - Tom Ziegler
- Department of Chemistry, University of Calgary, Calgary, Alberta, Canada, T2N 1N4
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22
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Grove LE, Brunold TC. SECOND-SPHERE TUNING OF THE METAL ION REDUCTION POTENTIALS IN IRON AND MANGANESE SUPEROXIDE DISMUTASES. COMMENT INORG CHEM 2008. [DOI: 10.1080/02603590802429529] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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23
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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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24
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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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Kaltashov IA, Zhang M, Eyles SJ, Abzalimov RR. Investigation of structure, dynamics and function of metalloproteins with electrospray ionization mass spectrometry. Anal Bioanal Chem 2006; 386:472-81. [PMID: 16932945 DOI: 10.1007/s00216-006-0636-6] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2006] [Revised: 06/06/2006] [Accepted: 06/19/2006] [Indexed: 10/24/2022]
Abstract
Electrospray ionization mass spectrometry (ESI MS) has emerged recently as a powerful tool for analyzing many structural and behavioral aspects of metalloproteins in great detail. In this review we discuss recent developments in the field, placing particular emphasis on the unique features of ESI MS that lend themselves to metalloprotein characterization at a variety of levels. Direct mass measurement enables the determination of protein-metal ion binding stoichiometry in solution and metalloprotein higher order structure in the case of multi-subunit proteins. MS techniques have been developed for determining the locations of metal-binding centers, metal oxidation states and reaction intermediates of metal-containing enzymes. Other ESI MS techniques are also discussed, such as protein ion charge state distributions and hydrogen/deuterium exchange studies, which can be used to measure metal binding affinities and to shed light on vital dynamic aspects of the functional properties of metalloproteins endowed by metal binding.
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Affiliation(s)
- Igor A Kaltashov
- Department of Chemistry, University of Massachusetts-Amherst, 710 North Pleasant Street, Amherst, MA 01003, USA.
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Delgado-Jaime MU, Conrad JC, Fogg DE, Kennepohl P. X-ray absorption methods for the determination of Ru–Cl bond covalency in olefin metathesis catalysts: On the normalization of chlorine K-edges in ruthenium complexes. Inorganica Chim Acta 2006. [DOI: 10.1016/j.ica.2005.12.058] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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27
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Gaggelli E, Kozlowski H, Valensin D, Valensin G. Copper Homeostasis and Neurodegenerative Disorders (Alzheimer's, Prion, and Parkinson's Diseases and Amyotrophic Lateral Sclerosis). Chem Rev 2006; 106:1995-2044. [PMID: 16771441 DOI: 10.1021/cr040410w] [Citation(s) in RCA: 1230] [Impact Index Per Article: 68.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Elena Gaggelli
- Department of Chemistry, University of Siena, Via Aldo Moro 2, Siena 53100, Italy
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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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Selective Conversion of Hydrocarbons with H2O2 Using Biomimetic Non-heme Iron and Manganese Oxidation Catalysts. ADVANCES IN INORGANIC CHEMISTRY 2006. [DOI: 10.1016/s0898-8838(05)58002-4] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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30
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Solomon EI, Szilagyi RK, DeBeer George S, Basumallick L. Electronic Structures of Metal Sites in Proteins and Models: Contributions to Function in Blue Copper Proteins. Chem Rev 2004; 104:419-58. [PMID: 14871131 DOI: 10.1021/cr0206317] [Citation(s) in RCA: 669] [Impact Index Per Article: 33.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Edward I Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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Lehnert N, Fujisawa K, Solomon EI. Electronic structure and reactivity of high-spin iron--alkyl- and--pterinperoxo complexes. Inorg Chem 2003; 42:469-81. [PMID: 12693229 DOI: 10.1021/ic020496g] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The spectroscopic properties and electronic structure of the four-coordinate high-spin [FeIII(L3)(OOtBu)]+ complex (1; L3 = hydrotris(3-tert-butyl-5-isopropyl-1-pyrazolyl)borate; tBu = tert-butyl) are investigated and compared to the six-coordinated high-spin [Fe(6-Me3TPA)(OHx)(OOtBu)]x+ system (TPA = tris(2-pyridylmethyl)amine, x = 1 or 2) studied earlier [Lehnert, N.; Ho, R. Y. N.; Que, L., Jr.; Solomon, E. I. J. Am. Chem. Soc. 2001, 123, 12802-12816]. Complex 1 is characterized by Raman features at 889 and 830 cm-1 which are assigned to the O-O stretch (mixed with the symmetric C-C stretch) and a band at 625 cm-1 that corresponds to nu(Fe-O). The UV-vis spectrum shows a charge-transfer (CT) transition at 510 nm from the alkylperoxo pi v* (v = vertical to C-O-O plane) to a d orbital of Fe(III). A second CT is identified from MCD at 370 nm that is assigned to a transition from pi h* (h = horizontal to C-O-O plane) to an Fe(III) d orbital. For the TPA complex the pi v* CT is at 560 nm while the pi h* CT is to higher energy than 250 nm. These spectroscopic differences between four- and six-coordinate Fe(III)-OOR complexes are interpreted on the basis of their different ligand fields. In addition, the electronic structure of Fe-OOPtn complexes with the biologically relevant pterinperoxo ligand are investigated. Substitution of the tert-butyl group in 1 by pterin leads to the corresponding Fe(III)-OOPtn species (2), which shows a stronger electron donation from the peroxide to Fe(III) than 1. This is related to the lower ionization potential of pterin. Reduction of 2 by one electron leads to the Fe(II)-OOPtn complex (3), which is relevant as a model for potential intermediates in pterin-dependent hydroxylases. However, in the four-coordinate ligand field of 3, the additional electron is located in a nonbonding d orbital of iron. Hence, the pterinperoxo ligand is not activated for heterolytic cleavage of the O-O bond in this system. This is also evident from the calculated reaction energies that are endothermic by at least 20 kcal/mol.
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Affiliation(s)
- Nicolai Lehnert
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA
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Abstract
Spectroscopic and theoretical investigations of the geometric and electronic structures of mononuclear and binuclear copper sites in proteins help in understanding the contributions of these proteins to biological electron transfer. Spectroscopically calibrated density functional theory calculations, which give reasonable bonding descriptions in both ground- and excited-states, define the role of the protein in determining the geometric and electronic structure of the active site.
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Affiliation(s)
- Robert K Szilagyi
- Department of Chemistry, Stanford University, Stanford, CA 94305, USA
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Lehnert N, Ho RY, Que L, Solomon EI. Electronic structure of high-spin iron(III)-alkylperoxo complexes and its relation to low-spin analogues: reaction coordinate of O-O bond homolysis. J Am Chem Soc 2001; 123:12802-16. [PMID: 11749538 DOI: 10.1021/ja011450+] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The spectroscopic properties of the high-spin Fe(III)-alkylperoxo model complex [Fe(6-Me(3)TPA)(OH(x))(OO(t)Bu)](x)(+) (1; TPA = tris(2-pyridylmethyl)amine, (t)Bu = tert-butyl, x = 1 or 2) are defined and related to density functional calculations of corresponding models in order to determine the electronic structure and reactivity of this system. The Raman spectra of 1 show four peaks at 876, 842, 637, and 469 cm(-1) that are assigned with the help of normal coordinate analysis, and corresponding force constants have been determined to be 3.55 mdyn/A for the O-O and 2.87 mdyn/A for the Fe-O bond. Complex 1 has a broad absorption feature around 560 nm that is assigned to a charge-transfer (CT) transition from the alkylperoxo to a t(2g) d orbital of Fe(III) with the help of resonance Raman profiles and MCD spectroscopy. An additional contribution to the Fe-O bond arises from a sigma interaction between and an e(g) d orbital of iron. The electronic structure of 1 is compared to the related low-spin model complex [Fe(TPA)(OH(x))(OO(t)Bu)](x)(+) and the reaction coordinate for O-O homolysis is explored for both the low-spin and the high-spin Fe(III)-alkylperoxo systems. Importantly, there is a barrier for homolytic cleavage of the O-O bond on the high-spin potential energy surface that is not present for the low-spin complex, which is therefore nicely set up for O-O homolysis. This is reflected by the electronic structure of the low-spin complex having a strong Fe-O and a weak O-O bond due to a strong Fe-O sigma interaction. In addition, the reaction coordinate of the Fe-O homolysis has been investigated, which is a possible decay pathway for the high-spin system, but which is thermodynamically unfavorable for the low-spin complex.
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Affiliation(s)
- N Lehnert
- Department of Chemistry, Stanford University, Stanford, CA 94305-5080, USA
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Solomon EI. Invited award contribution for ACS Award in Inorganic Chemistry. Geometric and electronic structure contributions to function in bioinorganic chemistry: active sites in non-heme iron enzymes. Inorg Chem 2001; 40:3656-69. [PMID: 11442362 DOI: 10.1021/ic010348a] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Spectroscopy has played a major role in the definition of structure/function correlations in bioinorganic chemistry. The importance of spectroscopy combined with electronic structure calculations is clearly demonstrated by the non-heme iron enzymes. Many members of this large class of enzymes activate dioxygen using a ferrous active site that has generally been difficult to study with most spectroscopic methods. A new spectroscopic methodology has been developed utilizing variable temperature, variable field magnetic circular dichroism, which enables one to obtain detailed insight into the geometric and electronic structure of the non-heme ferrous active site and probe its reaction mechanism on a molecular level. This spectroscopic methodology is presented and applied to a number of key mononuclear non-heme iron enzymes leading to a general mechanistic strategy for O2 activation. These studies are then extended to consider the new features present in the binuclear non-heme iron enzymes and applied to understand (1) the mechanism of the two electron/coupled proton transfer to dioxygen binding to a single iron center in hemerythrin and (2) structure/function correlations over the oxygen-activating enzymes stearoyl-ACP Delta9-desaturase, ribonucleotide reductase, and methane monooxygenase. Electronic structure/reactivity correlations for O2 activation by non-heme relative to heme iron enzymes will also be developed.
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Affiliation(s)
- E I Solomon
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
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