1
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Burgmayer SJN, Kirk ML. Advancing Our Understanding of Pyranopterin-Dithiolene Contributions to Moco Enzyme Catalysis. Molecules 2023; 28:7456. [PMID: 38005178 PMCID: PMC10673323 DOI: 10.3390/molecules28227456] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 10/23/2023] [Accepted: 10/24/2023] [Indexed: 11/26/2023] Open
Abstract
The pyranopterin dithiolene ligand is remarkable in terms of its geometric and electronic structure and is uniquely found in mononuclear molybdenum and tungsten enzymes. The pyranopterin dithiolene is found coordinated to the metal ion, deeply buried within the protein, and non-covalently attached to the protein via an extensive hydrogen bonding network that is enzyme-specific. However, the function of pyranopterin dithiolene in enzymatic catalysis has been difficult to determine. This focused account aims to provide an overview of what has been learned from the study of pyranopterin dithiolene model complexes of molybdenum and how these results relate to the enzyme systems. This work begins with a summary of what is known about the pyranopterin dithiolene ligand in the enzymes. We then introduce the development of inorganic small molecule complexes that model aspects of a coordinated pyranopterin dithiolene and discuss the results of detailed physical studies of the models by electronic absorption, resonance Raman, X-ray absorption and NMR spectroscopies, cyclic voltammetry, X-ray crystallography, and chemical reactivity.
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Affiliation(s)
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, Albuquerque, NM 87131, USA
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2
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Kirk ML, Lepluart J, Yang J. Resonance Raman spectroscopy of pyranopterin molybdenum enzymes. J Inorg Biochem 2022; 235:111907. [PMID: 35932756 PMCID: PMC10575615 DOI: 10.1016/j.jinorgbio.2022.111907] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 05/16/2022] [Accepted: 06/16/2022] [Indexed: 10/17/2022]
Abstract
Resonance Raman spectroscopy (rR) is a powerful spectroscopic probe that is widely used for studying the geometric and electronic structure of metalloproteins. In this focused review, we detail how resonance Raman spectroscopy has contributed to a greater understanding of electronic structure, geometric structure, and the reaction mechanisms of pyranopterin molybdenum enzymes. The review focuses on the enzymes sulfite oxidase (SO), dimethyl sulfoxide reductase (DMSOR), xanthine oxidase (XO), and carbon monoxide dehydrogenase. Specifically, we highlight how Mo-Ooxo, Mo-Ssulfido, Mo-Sdithiolene, and dithiolene CC vibrational modes, isotope and heavy atom perturbations, resonance enhancement, and associated Raman studies of small molecule analogs have provided detailed insight into the nature of these metalloenzyme active sites.
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Affiliation(s)
- Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States.
| | - Jesse Lepluart
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, NM 87131-0001, United States
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3
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Gates C, Varnum H, Getty C, Loui N, Chen J, Kirk ML, Yang J, Nieter Burgmayer SJ. Protonation and Non-Innocent Ligand Behavior in Pyranopterin Dithiolene Molybdenum Complexes. Inorg Chem 2022; 61:13728-13742. [PMID: 36000991 PMCID: PMC10544801 DOI: 10.1021/acs.inorgchem.2c01234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The complex [TEA][Tp*MoIV(O)(S2BMOPP)] (1) [TEA = tetraethylammonium, Tp* = tris(3,5-dimethylpyrazolyl)hydroborate, and BMOPP = 6-(3-butynyl-2-methyl-2-ol)-2-pivaloyl pterin] is a structural analogue of the molybdenum cofactor common to all pyranopterin molybdenum enzymes because it possesses a pyranopterin-ene-1,2-dithiolate ligand (S2BMOPP) that exists primarily in the ring-closed pyrano structure as a resonance hybrid of ene-dithiolate and thione-thiolate forms. Compound 1, the protonated [Tp*MoIV(O)(S2BMOPP-H)] (1-H) and one-electron-oxidized [Tp*MoV(O)(S2BMOPP)] [1-Mo(5+)] species have been studied using a combination of electrochemistry, electronic absorption, and electron paramagnetic resonance (EPR) spectroscopy. Additional insight into the nature of these molecules has been derived from electronic structure computations. Differences in dithiolene C-S bond lengths correlate with relative contributions from both ene-dithiolate and thione-thiolate resonance structures. Upon protonation of 1 to form 1-H, large spectroscopic changes are observed with transitions assigned as Mo(xy) → pyranopterin metal-to-ligand charge transfer and dithiolene → pyranopterin intraligand charge transfer, respectively, and this underscores a dramatic change in electronic structure between 1 and 1-H. The changes in electronic structure that occur upon protonation of 1 are also reflected in a large >300 mV increase in the Mo(V/IV) redox potential for 1-H, resulting from the greater thione-thiolate resonance contribution and decreased charge donation that stabilize the Mo(IV) state in 1-H with respect to one-electron oxidation. EPR spin Hamiltonian parameters for one-electron-oxidized 1-Mo(5+) and uncyclized [Tp*MoV(O)(S2BDMPP)] [3-Mo(5+)] [BDMPP = 6-(3-butynyl-2,2-dimethyl)-2-pivaloyl pterin] are very similar to each other and to those of [Tp*MoVO(bdt)] (bdt = 1,2-ene-dithiolate). This indicates that the dithiolate form of the ligand dominates at the Mo(V) level, consistent with the demand for greater S → Mo charge donation and a corresponding increase in Mo-S covalency as the oxidation state of the metal is increased. Protonation of 1 represents a simple reaction that models how the transfer of a proton from neighboring acidic amino acid residues to the Mo cofactor at a nitrogen atom within the pyranopterin dithiolene (PDT) ligand in pyranopterin molybdenum enzymes can impact the electronic structure of the Mo-PDT unit. This work also illustrates how pyran ring-chain tautomerization drives changes in resonance contributions to the dithiolene chelate and may adjust the reduction potential of the Mo ion.
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Affiliation(s)
- Cassandra Gates
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Haley Varnum
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Catherine Getty
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Natalie Loui
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Ju Chen
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
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4
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Dille SA, Colston KJ, Ratvasky SC, Pu J, Basu P. Interligand communication in a metal mediated LL'CT system - a case study. RSC Adv 2021; 11:24381-24386. [PMID: 34354823 PMCID: PMC8285364 DOI: 10.1039/d1ra04716g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 07/06/2021] [Indexed: 11/22/2022] Open
Abstract
A series of oxo-Mo(iv) complexes, [MoO(Dt2−)(Dt0)] (where Dt2− = benzene-1,2-dithiol (bdt), toluene-3,4-dithiol (tdt), quinoxaline-2,3-dithiol (qdt), or 3,6-dichloro-benzene-1,2-dithiol (bdtCl2); Dt0 = N,N′-dimethylpiperazine-2,3-dithione (Me2Dt0) or N,N′-diisopropylpiperazine-2,3-dithione (iPr2Dt0)), possessing a fully oxidized and a fully reduced dithiolene ligand have been synthesized and characterized. The assigned oxidation states of coordinated dithiolene ligands are supported with spectral and crystallographic data. The molecular structure of [MoO(tdt)(iPr2Dt0)] (6) demonstrates a large ligand fold angle of 62.6° along the S⋯S vector of the Dt0 ligand. The electronic structure of this system is probed by density functional theory (DFT) calculations. The HOMO is largely localized on the Dt2− ligand while virtual orbitals are mostly Mo and Dt0 in character. Modeling the electronic spectrum of 6 with time dependent (TD) DFT calculations attributes the intense low energy transition at ∼18 000 cm−1 to a ligand-to-ligand charge transfer (LL′CT). The electron density difference map (EDDM) for the low energy transition depicts the electron rich Dt2− ligand donating charge density to the redox-active orbitals of the electron deficient Dt0 ligand. Electronic communication between dithiolene ligands is facilitated by a Mo-monooxo center and distortion about its primary coordination sphere. The interligand communication between non-innocent dithiolene ligands of different oxidation states has been described in a Mo system. The fully reduced ene-dithiolate (Dt2−) acts as a donor moiety to the oxidized dithione (Dt0) in an LL′CT process.![]()
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Affiliation(s)
- Sara A Dille
- Department of Chemistry and Chemical Biology, Indiana University - Purdue University Indianapolis Indianapolis IN 46202 USA
| | - Kyle J Colston
- Department of Chemistry and Chemical Biology, Indiana University - Purdue University Indianapolis Indianapolis IN 46202 USA
| | - Stephen C Ratvasky
- Department of Chemistry and Biochemistry, Duquesne University Pittsburgh PA 15282 USA
| | - Jingzhi Pu
- Department of Chemistry and Chemical Biology, Indiana University - Purdue University Indianapolis Indianapolis IN 46202 USA
| | - Partha Basu
- Department of Chemistry and Chemical Biology, Indiana University - Purdue University Indianapolis Indianapolis IN 46202 USA
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5
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Dille SA, Colston KJ, Mogesa B, Cassell J, Perera E, Zeller M, Basu P. The Impact of Ligand Oxidation State and Fold Angle on the Charge Transfer Processes of Mo
IV
O‐Dithione Complexes. Eur J Inorg Chem 2021. [DOI: 10.1002/ejic.202001155] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sara A. Dille
- School Science Department of Chemistry and Chemical Biology Indiana University-Purdue University Indianapolis 402 N. Blackford St. Indianapolis IN 462020 USA
| | - Kyle J. Colston
- School Science Department of Chemistry and Chemical Biology Indiana University-Purdue University Indianapolis 402 N. Blackford St. Indianapolis IN 462020 USA
| | - Benjamin Mogesa
- Bayer School of Natural Science Department of Chemistry and Biochemistry Duquesne University 600 Forbes Ave. Pittsburgh PA 15282 USA
| | - Joseph Cassell
- School Science Department of Chemistry and Chemical Biology Indiana University-Purdue University Indianapolis 402 N. Blackford St. Indianapolis IN 462020 USA
| | - Eranda Perera
- Bayer School of Natural Science Department of Chemistry and Biochemistry Duquesne University 600 Forbes Ave. Pittsburgh PA 15282 USA
| | - Matthias Zeller
- College of Science Department of Chemistry Purdue University 560 Oval Dr. West Lafayette In 47907 USA
| | - Partha Basu
- School Science Department of Chemistry and Chemical Biology Indiana University-Purdue University Indianapolis 402 N. Blackford St. Indianapolis IN 462020 USA
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6
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Colston KJ, Dille SA, Mogesa B, Brant J, Nemykin VN, Zeller M, Basu P. Syntheses, spectroscopic, redox, and structural properties of homoleptic Iron(III/II) dithione complexes. RSC Adv 2020; 10:38294-38303. [PMID: 35517554 PMCID: PMC9057267 DOI: 10.1039/d0ra07371g] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2020] [Accepted: 10/10/2020] [Indexed: 11/21/2022] Open
Abstract
Two sets of FeIII/II dithione complexes [FeII(iPr2Dt0)3][PF6]2 ([1][PF6]2), [FeII(Me2Dt0)3][PF6]2 ([2][PF6]2), and [FeIII(iPr2Dt0)3][PF6]3 ([3][PF6]3), [FeIII(Me2Dt0)3][PF6]3 ([4][PF6]3), and compound [FeIII(iPr2Dt0)3][FeCl4][PF]2 ([3][FeCl4][PF6]2) were synthesized from N,N′-diisopropyl piperazine-2,3-dithione (iPr2Dt0) and N,N′-dimethyl piperazine-2,3-dithione (Me2Dt0) ligands. Complexes [1][PF6]2–[4][PF6]3 have been characterized by NMR, IR, and UV-visible spectroscopies, and by electrochemistry. The molecular structures of [2][PF6]2 and [3][FeCl4][PF6]2 have been determined by X-ray crystallography. Complexes [2][PF6]2 and [3][FeCl4][PF6]2 both crystallized in the monoclinic space group P21/n. Both complexes exhibit distorted octahedral geometry and the three coordinated ligands in each complex exhibit different dithione folding. Complexes [1][PF6]2–[4][PF6]3 exhibit a single FeIII/II based couple and three quasi-reversible ligand-based redox couples. The electronic spectra of [1][PF6]2–[4][PF6]3 show intense MLCT bands that indicate strong mixing between metal and ligand orbitals. DFT calculations were used to provide a framework for understanding the electronic origin of their redox chemistry and spectroscopic features. Two sets of FeIII/II complexes, synthesized from N,N′-diisopropyl piperazine-2,3-dithione (iPr2Dt0) and N,N′-dimethyl piperazine-2,3-dithione (Me2Dt0) ligands, exhibit electronically asymmetrical ligands with metal–ligand orbital mixing.![]()
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Affiliation(s)
- Kyle J Colston
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis IN 46202 USA
| | - Sara A Dille
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis IN 46202 USA
| | - Benjamin Mogesa
- Department of Chemistry and Biochemistry, Duquesne University Pittsburgh PA 15282 USA
| | - Jacilynn Brant
- The Air Force Research Laboratory, Wright-Patterson AFB OH 45433 USA
| | - Victor N Nemykin
- Department of Chemistry, University of Tennessee Knoxville TN 37996 USA
| | - Matthias Zeller
- Department of Chemistry, Purdue University West Layfette IN 47907 USA
| | - Partha Basu
- Department of Chemistry and Chemical Biology, Indiana University-Purdue University Indianapolis IN 46202 USA
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7
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Basu P, Colston KJ, Mogesa B. Dithione, the antipodal redox partner of ene-1,2-dithiol ligands and their metal complexes. Coord Chem Rev 2020; 409:213211. [PMID: 38094102 PMCID: PMC10718511 DOI: 10.1016/j.ccr.2020.213211] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Defining the oxidation state of the central atom in a coordination compound is fundamental in understanding the electronic structure and provides a starting point for elucidating molecular properties. The presence of non-innocent ligand(s) can obscure the oxidation state of the central atom as the ligand contribution to the electronic structure is difficult to ascertain. Redox-active ligands, such as dithiolene ligands, are well known non-innocent ligands that can exist in both a fully reduced (Dt2-) and fully oxidized (Dt0) states. Complexes containing the fully oxidized dithione state of the ligand are uncommon and only a few have been completely characterized. Dithione ligands are of interest due to their electron-deficient nature and ability to act as an electron acceptor for more electron-rich moieties, such as other dithiolene ligands or metal centers. This article focuses the syntheses, structures, and metal coordination, particularly coordination compounds, of dithione ligands. Various examples of mono, bis, and tris dithione complexes are discussed.
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Affiliation(s)
- Partha Basu
- Department of Chemistry and Chemical Biology, IUPUI, Indianapolis, IN 46202, United States
| | - Kyle J. Colston
- Department of Chemistry and Chemical Biology, IUPUI, Indianapolis, IN 46202, United States
| | - Benjamin Mogesa
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282, United States
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8
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Abstract
Here we highlight past work on metal-dithiolene interactions and how the unique electronic structure of the metal-dithiolene unit contributes to both the oxidative and reductive half reactions in pyranopterin molybdenum and tungsten enzymes. The metallodithiolene electronic structures detailed here were interrogated using multiple ground and excited state spectroscopic probes on the enzymes and their small molecule analogs. The spectroscopic results have been interpreted in the context of bonding and spectroscopic calculations, and the pseudo-Jahn-Teller effect. The dithiolene is a unique ligand with respect to its redox active nature, electronic synergy with the pyranopterin component of the molybdenum cofactor, and the ability to undergo chelate ring distortions that control covalency, reduction potential, and reactivity in pyranopterin molybdenum and tungsten enzymes.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, Albuquerque, NM 87131-0001, USA
| | - John H. Enemark
- Department of Chemistry Biochemistry, University of Arizona, Tucson, AZ 85721, USA
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, Albuquerque, NM 87131-0001, USA
- Correspondence: ; Tel.: +1-505-277-5992
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9
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Colston KJ, Dille SA, Mogesa B, Astashkin AV, Brant JA, Zeller M, Basu P. Design, Synthesis, and Structure of Copper Dithione Complexes: Redox‐Dependent Charge Transfer. Eur J Inorg Chem 2019. [DOI: 10.1002/ejic.201901222] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- Kyle J. Colston
- Department of Chemistry and Chemical Biology Indiana University‐Purdue University Indianapolis 402 N. Blackford Street 46202 Indianapolis IN USA
| | - Sara A. Dille
- Department of Chemistry and Chemical Biology Indiana University‐Purdue University Indianapolis 402 N. Blackford Street 46202 Indianapolis IN USA
| | - Benjamin Mogesa
- Department of Chemistry and Biochemistry Duquesne University 15282 Pittsburgh PA USA
| | - Andrei V. Astashkin
- Department of Chemistry and Biochemistry University of Arizona 85721 Tucson AZ USA
| | - Jacilynn A. Brant
- The Air Force Research Laboratory Aerospace Systems Directorate 1950 Fifth Street, Building 18 45433 Wright‐Patterson Air Force Base Ohio USA
| | - Matthias Zeller
- Department of Chemistry Purdue University 560 Oval Drive 47907 West Lafayette IN USA
| | - Partha Basu
- Department of Chemistry and Chemical Biology Indiana University‐Purdue University Indianapolis 402 N. Blackford Street 46202 Indianapolis IN USA
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10
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Gisewhite DR, Nagelski AL, Cummins DC, Yap GPA, Burgmayer SJN. Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl-Dithiolene Promoting Pyran Cyclization. Inorg Chem 2019; 58:5134-5144. [PMID: 30942584 PMCID: PMC6572731 DOI: 10.1021/acs.inorgchem.9b00194] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Mononuclear Mo and W enzymes require a unique ligand known as molybdopterin (MPT). This ligand binds the metal through a dithiolene chelate, and the dithiolene bridges a reduced pyranopterin group. Pyran scission and formation have been proposed as a reaction of the MPT ligand that may occur within the enzymes to adjust reactivity at the Mo atom. We address this issue by investigating oxo-Mo(IV) model complexes containing dithiolenes substituted by pterin or quinoxaline and a hydroxyalkyl poised to form a pyran ring. While the pterin-dithiolene model complex exhibits a low energy, reversible pyran cyclization, here we report that pyran cyclization does not spontaneously occur in the quinoxalyl-dithiolene model. However, protonating the quinoxalyl-dithiolene model induces pyran cyclization forming an unstable, pyrano-quinoxalyl-dithiolene complex which subsequently dehydrates and rearranges to a pyrrolo-quinoxlyl-dithiolene complex that was previously characterized. The protonated pyrano-quinoxalyl-dithiolene complex was characterized by absorption spectroscopy and cyclic voltammetry, and these results suggest pyran cyclization leads to a significant change in the Mo electronic structure exhibited as a strong intraligand charge transfer (ILCT) transition and 370 mV positive shift of the Mo(V/IV) reduction potential. The influence of protonation on quinoxaline reactivity supports the hypothesis that the local protein environment in the second coordination sphere of molybdenum cofactor (Moco) could control pyran cyclization. The results also demonstrate that the remarkable chemical reactivity of the pterin-dithiolene ligand is subtly distinct and not reproduced by the simpler quinoxaline analog that is often used to replace pterin in synthetic Moco models.
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Affiliation(s)
- Douglas R. Gisewhite
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Alexandra L. Nagelski
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
| | - Daniel C. Cummins
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
| | - Glenn P. A. Yap
- Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, United States
| | - Sharon J. N. Burgmayer
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
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11
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Gisewhite DR, Yang J, Williams BR, Esmail A, Stein B, Kirk ML, Burgmayer SJN. Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor. J Am Chem Soc 2018; 140:12808-12818. [PMID: 30200760 DOI: 10.1021/jacs.8b05777] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
The large family of mononuclear molybdenum and tungsten enzymes all possess the special ligand molybdopterin (MPT), which consists of a metal-binding dithiolene chelate covalently bound to a pyranopterin group. MPT pyran cyclization/scission processes have been proposed to modulate the reactivity of the metal center during catalysis. We have designed several small-molecule models for the Mo-MPT cofactor that allow detailed investigation into how pyran cyclization modulates electronic communication between the dithiolene and pterin moieties and how this cyclization alters the electronic environment of the molybdenum catalytic site. Using a combination of cyclic voltammetry, vibrational spectroscopy (FT-IR and rR), electronic absorption spectroscopy, and X-ray absorption spectroscopy, distinct changes in the Mo≡O stretching frequency, Mo(V/IV) reduction potential, and electronic structure across the pterin-dithiolene ligand are observed as a function of pyran ring closure. The results are significant, for they reveal that a dihydropyranopterin is electronically coupled into the Mo-dithiolene group due to a coplanar conformation of the pterin and dithiolene units, providing a mechanism for the electron-deficient pterin to modulate the Mo environment. A spectroscopic signature identified for the dihydropyranopterin-dithiolene ligand on Mo is a strong dithiolene → pterin charge transfer transition. In the absence of a pyran group bridge between pterin and dithiolene, the pterin rotates out of plane, largely decoupling the system. The results support a hypothesis that pyran cyclization/scission processes in MPT may function as a molecular switch to electronically couple and decouple the pterin and dithiolene to adjust the redox properties in certain pyranopterin molybdenum enzymes.
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Affiliation(s)
- Douglas R Gisewhite
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Benjamin R Williams
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Alisha Esmail
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
| | - Benjamin Stein
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC03 2060, 1 University of New Mexico , Albuquerque , New Mexico 87131-0001 , United States
| | - Sharon J N Burgmayer
- Department of Chemistry , Bryn Mawr College , Bryn Mawr , Pennsylvania 19010 , United States
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12
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Fernández L, Pérez-Pla FF, Tuñón I, Llopis E. DFT Study on the Interaction of Tris(benzene-1,2-dithiolato)molybdenum Complex with Water. A Hydrolysis Mechanism Involving a Feasible Seven-Coordinate Aquomolybdenum Intermediate. J Phys Chem A 2016; 120:9636-9646. [PMID: 27933913 DOI: 10.1021/acs.jpca.6b10233] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
In the present work, the reactivity of the tris(benzene-1,2-dithiolato)molybdenum complex ([Mo(bdt)3]) toward water is studied by means of the density functional theory (DFT). DFT calculations were performed using the M06, B3P86, and B3PW91 hybrid functionals for comparison purposes. The M06 method was employed to elucidate the reaction pathway, relative stability of the intermediate products, nature of the Mo-S bond cleavage, and electronic structure of the involved molybdenum species. This functional was also used to study the transference of electrons from the molybdenum center toward the ligands. The reaction pathway confirms that [Mo(bdt)3] undergoes hydrolysis, yielding dihydroxo-bis(benzene-1,2-dithiolato)molybdenum complex ([Mo(OH)2(bdt)2]) and benzenedithiol. The reaction takes place through seven transition structures, one of them involving an aquo seven-coordinate molybdenum intermediate stabilized by a lone pair (LP) LPO→LPMo hyperconjugative interaction. This heptacoordinate species allows understanding of the observed oxygen atom exchange between water and tertiary phosphines mediated by these complexes. Calculations also show that [Mo(C2H4S2)3] and [Mo(OH)2(C2H4S2)2] have d2 and d0 electronic configuration, and hence an electron pair must be transferred during the course of the hydrolysis. The frontier molecular orbital (FMO) analysis concludes that the electron pair is transferred in the rupture of the second Mo-S bond, from the occupied donating Mo dx2-y2 orbital to the unoccupied C2H4(SH)2 S-C σ* ligand orbital. This result is supported by the bond dissociation energy calculations, which demonstrate that the neutral dissociation of the second Mo-S bond is energetically the more favorable.
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Affiliation(s)
- Lorenzo Fernández
- Institut de Cíencia dels Materials (ICMUV) , c/Catedrático Beltrán 2, 46980, Valencia, Spain
| | - Francisco F Pérez-Pla
- Institut de Cíencia dels Materials (ICMUV) , c/Catedrático Beltrán 2, 46980, Valencia, Spain
| | - Iñaki Tuñón
- Departamento de Química Física, Universitat de València , Dr. Moliner 50, 46100, Burjassot, Valencia, Spain
| | - Elisa Llopis
- Institut de Cíencia dels Materials (ICMUV) , c/Catedrático Beltrán 2, 46980, Valencia, Spain
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Ratvasky SC, Mogesa B, van Stipdonk MJ, Basu P. A mixed valence zinc dithiolene system with spectator metal and reactor ligands. Polyhedron 2016; 114:370-377. [PMID: 27667891 DOI: 10.1016/j.poly.2016.01.023] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Neutral complexes of zinc with N,N'-diisopropylpiperazine-2,3-dithione ( i Pr2Dt0) and N,N'-dimethylpiperazine-2,3-dithione (Me2Dt0) with chloride or maleonitriledithiolate (mnt2-) as coligands have been synthesized and characterized. The molecular structures of these zinc complexes have been determined using single crystal X-ray diffractometry. Complexes recrystallize in monoclinic P type systems with zinc adopting a distorted tetrahedral geometry. Two zinc complexes with mixed-valent dithiolene ligands exhibit ligand-to-ligand charge transfer bands. Optimized geometries, molecular vibrations and electronic structures of charge-transfer complexes were calculated using density functional theory (B3LYP/6-311G+(d,p) level). Redox orbitals are shown to be almost exclusively ligand in nature, with a HOMO based heavily on the electron-rich maleonitriledithiolate ligand, and a LUMO comprised mostly of the electron-deficient dithione ligand. Charge transfer is thus believed to proceed from dithiolate HOMO to dithione LUMO, showing ligand-to-ligand redox interplay across a d10 metal.
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Affiliation(s)
- Stephen C Ratvasky
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282
| | - Benjamin Mogesa
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282
| | | | - Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282
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Yang J, Mogesa B, Basu P, Kirk ML. Large Ligand Folding Distortion in an Oxomolybdenum Donor-Acceptor Complex. Inorg Chem 2015; 55:785-93. [PMID: 26692422 DOI: 10.1021/acs.inorgchem.5b02252] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Interligand charge transfer is examined in the novel metallo-dithiolene complex MoO(SPh)2((i)Pr2Dt(0)) (where (i)Pr2Dt(0) = N,N'-isopropyl-piperazine-2,3-dithione). The title complex displays a remarkable 70° "envelope"-type fold of the five-membered dithiolene ring, which is bent upward toward the terminal oxo ligand. A combination of electronic absorption and resonance Raman spectroscopies have been used to probe the basic electronic structure responsible for the large fold-angle distortion. The intense charge transfer transition observed at ∼18 000 cm(-1) is assigned as a thiolate → dithione ligand-to-ligand charge transfer (LL'CT) transition that also possesses Mo(IV) → dithione charge transfer character. Strong orbital mixing between occupied and virtual orbitals with Mo(x(2)-y(2)) orbital character is derived from a strong pseudo Jahn-Teller effect, which drives the large fold-angle distortion to yield a double-well potential in the electronic ground state.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico , MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
| | - Benjamin Mogesa
- Department of Chemistry and Biochemistry, Duquesne University , Pittsburgh, Pennsylvania 15282, United States
| | - Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University , Pittsburgh, Pennsylvania 15282, United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico , MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, United States
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Pimkov IV, Serli-Mitasev B, Peterson AA, Ratvasky SC, Hammann B, Basu P. Designing the Molybdopterin Core through Regioselective Coupling of Building Blocks. Chemistry 2015; 21:17057-72. [DOI: 10.1002/chem.201502845] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2015] [Indexed: 01/08/2023]
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Wu SY, Rothery RA, Weiner JH. Pyranopterin Coordination Controls Molybdenum Electrochemistry in Escherichia coli Nitrate Reductase. J Biol Chem 2015; 290:25164-73. [PMID: 26297003 DOI: 10.1074/jbc.m115.665422] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Indexed: 11/06/2022] Open
Abstract
We test the hypothesis that pyranopterin (PPT) coordination plays a critical role in defining molybdenum active site redox chemistry and reactivity in the mononuclear molybdoenzymes. The molybdenum atom of Escherichia coli nitrate reductase A (NarGHI) is coordinated by two PPT-dithiolene chelates that are defined as proximal and distal based on their proximity to a [4Fe-4S] cluster known as FS0. We examined variants of two sets of residues involved in PPT coordination: (i) those interacting directly or indirectly with the pyran oxygen of the bicyclic distal PPT (NarG-Ser(719), NarG-His(1163), and NarG-His(1184)); and (ii) those involved in bridging the two PPTs and stabilizing the oxidation state of the proximal PPT (NarG-His(1092) and NarG-His(1098)). A S719A variant has essentially no effect on the overall Mo(VI/IV) reduction potential, whereas the H1163A and H1184A variants elicit large effects (ΔEm values of -88 and -36 mV, respectively). Ala variants of His(1092) and His(1098) also elicit large ΔEm values of -143 and -101 mV, respectively. An Arg variant of His(1092) elicits a small ΔEm of +18 mV on the Mo(VI/IV) reduction potential. There is a linear correlation between the molybdenum Em value and both enzyme activity and the ability to support anaerobic respiratory growth on nitrate. These data support a non-innocent role for the PPT moieties in controlling active site metal redox chemistry and catalysis.
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Affiliation(s)
- Sheng-Yi Wu
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Richard A Rothery
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
| | - Joel H Weiner
- From the Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
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17
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Mogesa B, Perera E, Rhoda HM, Gibson JK, Oomens J, Berden G, van Stipdonk MJ, Nemykin VN, Basu P. Solution, Solid, and Gas Phase Studies on a Nickel Dithiolene System: Spectator Metal and Reactor Ligand. Inorg Chem 2015; 54:7703-16. [PMID: 26244772 DOI: 10.1021/acs.inorgchem.5b00531] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The syntheses of cationic nickel complexes using N,N'-dimethyl piperazine 2,3-dithione (Me2Dt(0)) and N,N'-diisopropyl piperazine 2,3-dithione ((i)Pr2Dt(0)) ligands are reported. These ligands were used in synthesizing bis and tris(dithione)Ni(II) complexes as tetrafluoroborate or hexafluorophosphate salts, i.e., [Ni((i)Pr2Dt(0))2][BF4]2 ([1a][BF4]2), [Ni((i)Pr2Dt(0))2][PF6]2 ([1a][PF6]2), [Ni(Me2Dt(0))2][BF4]2 ([1b][BF4]2), [Ni((i)Pr2Dt(0))3][BF4]2 ([2a][BF4]2), and [Ni((i)Pr2Dt(0))3][PF6]2 ([2a][PF6]2), respectively. Complex [2a][PF6]2 was isolated from a methanolic solution of [1a][PF6]2. Compound [1a][BF4]2 crystallizes in a trigonal crystal system (space group, P31/c) and exhibits unique packing features, whereas [2a][BF4]2 crystallizes in a monoclinic (P21/n) space group. Cyclic voltammograms of [1a][BF4]2 and [1b][BF4]2 are indicative of four reduction processes associated with stepwise single-electron reduction of the ligands. Spectroelectrochemical experiments on [1a][BF4]2 exhibit an intervalence charge transfer (IVCT) transition as a spectroscopic signature of the mixed-valence [Ni((i)Pr2Dt(0))((i)Pr2Dt(1-))](-) species. Analysis of this IVCT band suggests that this ligand based mixed valence complex, [Ni((i)Pr2Dt(0))((i)Pr2Dt(1-))](-), behaves more like a traditional class II/III metal based mixed-valence complex. The density functional theory (DFT) and time dependent DFT calculations provide a theoretical framework for understanding the electronic structures and the nature of excited states of the target compounds that are consistent with their spectroscopic and redox properties. Vibrational spectra of [1a](2+) and [2a](2+) were investigated as discrete species in the gas phase using infrared multiple photon dissociation (IRMPD) spectroscopy.
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Affiliation(s)
- Benjamin Mogesa
- †Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
| | - Eranda Perera
- †Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
| | - Hannah M Rhoda
- ‡Department of Chemistry and Biochemistry, University of Minnesota-Duluth, Duluth, Minnesota 55812, United States
| | - John K Gibson
- §Chemical Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, United States
| | - Jos Oomens
- ∥Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands
| | - Giel Berden
- ∥Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands
| | - Michael J van Stipdonk
- †Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
| | - Victor N Nemykin
- ‡Department of Chemistry and Biochemistry, University of Minnesota-Duluth, Duluth, Minnesota 55812, United States
| | - Partha Basu
- †Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, Pennsylvania 15282, United States
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Basu P, Nieter Burgmayer SJ. Recent developments in the study of molybdoenzyme models. J Biol Inorg Chem 2015; 20:373-83. [PMID: 25578808 PMCID: PMC4336637 DOI: 10.1007/s00775-014-1228-0] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2014] [Accepted: 12/07/2014] [Indexed: 12/22/2022]
Abstract
Over the past two decades, a plethora of crystal structures of molybdenum enzymes has appeared in the literature providing a clearer picture of the enzymatic active sites and increasing the challenge to chemists to develop accurate models for those sites. In this minireview we discuss the most recent model studies aimed to reproduce detailed features of the pterin-dithiolene ligand, both as the uncoordinated form and as a chelate coordinated to molybdenum.
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Affiliation(s)
- Partha Basu
- Department of Chemistry and Biochemistry, Duquesne University, Pittsburgh, PA 15282
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Sparacino-Watkins C, Stolz JF, Basu P. Nitrate and periplasmic nitrate reductases. Chem Soc Rev 2014; 43:676-706. [PMID: 24141308 DOI: 10.1039/c3cs60249d] [Citation(s) in RCA: 189] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The nitrate anion is a simple, abundant and relatively stable species, yet plays a significant role in global cycling of nitrogen, global climate change, and human health. Although it has been known for quite some time that nitrate is an important species environmentally, recent studies have identified potential medical applications. In this respect the nitrate anion remains an enigmatic species that promises to offer exciting science in years to come. Many bacteria readily reduce nitrate to nitrite via nitrate reductases. Classified into three distinct types--periplasmic nitrate reductase (Nap), respiratory nitrate reductase (Nar) and assimilatory nitrate reductase (Nas), they are defined by their cellular location, operon organization and active site structure. Of these, Nap proteins are the focus of this review. Despite similarities in the catalytic and spectroscopic properties Nap from different Proteobacteria are phylogenetically distinct. This review has two major sections: in the first section, nitrate in the nitrogen cycle and human health, taxonomy of nitrate reductases, assimilatory and dissimilatory nitrate reduction, cellular locations of nitrate reductases, structural and redox chemistry are discussed. The second section focuses on the features of periplasmic nitrate reductase where the catalytic subunit of the Nap and its kinetic properties, auxiliary Nap proteins, operon structure and phylogenetic relationships are discussed.
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Pyranopterin conformation defines the function of molybdenum and tungsten enzymes. Proc Natl Acad Sci U S A 2012; 109:14773-8. [PMID: 22927383 DOI: 10.1073/pnas.1200671109] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have analyzed the conformations of 319 pyranopterins in 102 protein structures of mononuclear molybdenum and tungsten enzymes. These span a continuum between geometries anticipated for quinonoid dihydro, tetrahydro, and dihydro oxidation states. We demonstrate that pyranopterin conformation is correlated with the protein folds defining the three major mononuclear molybdenum and tungsten enzyme families, and that binding-site micro-tuning controls pyranopterin oxidation state. Enzymes belonging to the bacterial dimethyl sulfoxide reductase (DMSOR) family contain a metal-bis-pyranopterin cofactor, the two pyranopterins of which have distinct conformations, with one similar to the predicted tetrahydro form, and the other similar to the predicted dihydro form. Enzymes containing a single pyranopterin belong to either the xanthine dehydrogenase (XDH) or sulfite oxidase (SUOX) families, and these have pyranopterin conformations similar to those predicted for tetrahydro and dihydro forms, respectively. This work provides keen insight into the roles of pyranopterin conformation and oxidation state in catalysis, redox potential modulation of the metal site, and catalytic function.
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Kaim W. The Shrinking World of Innocent Ligands: Conventionaland Non-Conventional Redox-Active Ligands. Eur J Inorg Chem 2012. [DOI: 10.1002/ejic.201101359] [Citation(s) in RCA: 233] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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