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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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Kirk ML, Hille R. Spectroscopic Studies of Mononuclear Molybdenum Enzyme Centers. Molecules 2022; 27:molecules27154802. [PMID: 35956757 PMCID: PMC9370002 DOI: 10.3390/molecules27154802] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 06/26/2022] [Accepted: 06/29/2022] [Indexed: 02/06/2023] Open
Abstract
A concise review is provided of the contributions that various spectroscopic methods have made to our understanding of the physical and electronic structures of mononuclear molybdenum enzymes. Contributions to our understanding of the structure and function of each of the major families of these enzymes is considered, providing a perspective on how spectroscopy has impacted the field.
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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, USA
- Correspondence: (M.L.K.); (R.H.)
| | - Russ Hille
- Department of Biochemistry, Boyce Hall 1463, University of California, Riverside, CA 82521, USA
- Correspondence: (M.L.K.); (R.H.)
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5
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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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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 DOI: 10.1021/acs.inorgchem.9b00194] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [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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7
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Chrysochos N, Ahmadi M, Wahlefeld S, Rippers Y, Zebger I, Mroginski MA, Schulzke C. Comparison of molybdenum and rhenium oxo bis-pyrazine-dithiolene complexes - in search of an alternative metal centre for molybdenum cofactor models. Dalton Trans 2019; 48:2701-2714. [PMID: 30720825 DOI: 10.1039/c8dt04237c] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A pair of structurally precise analogues of molybdenum and rhenium complexes, [Et4N]/K2[MoO(prdt)2] and K[ReO(prdt)2] (prdt = pyrazine-2,3-dithiolene), were synthesized. These complexes serve as structural models for the active sites of bacterial molybdenum cofactor containing enzymes. They were comprehensively characterized and investigated by NMR, computationally supported IR and resonance Raman spectroscopy, cyclic voltammetry, mass spectrometry, elemental analysis and single-crystal X-ray diffraction. All compiled data are discussed in the context of comparing chemical and electronic structures and consequences thereof. This study constitutes the first investigation of a potential alternative Moco model system bearing rhenium as the central metal in an identical coordination environment to its molybdenum analogue. Structural evaluation revealed a slightly stronger M[double bond, length as m-dash]O bond in the rhenium complex in accordance with spectroscopic results, i.e. observed bond strengths. Thermodynamic parameters for the redox processes MoIV ↔ MoV and ReIV ↔ ReV were obtained by temperature dependent cyclic voltammetry. In contrast to molybdenum, rhenium loses entropy upon reduction and its redox potential is more temperature sensitive, indicating more significant differences than the respective diagonal relationship between the two metals in the periodic table might suggest and questioning rhenium's suitability as a functional artificial active site metal.
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Affiliation(s)
- Nicolas Chrysochos
- Institut für Biochemie, Universität Greifswald, Felix-Hausdorff-Straße 4, 17487 Greifswald, Germany.
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8
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Stein BW, Yang J, Mtei R, Wiebelhaus NJ, Kersi DK, LePluart J, Lichtenberger DL, Enemark JH, Kirk ML. Vibrational Control of Covalency Effects Related to the Active Sites of Molybdenum Enzymes. J Am Chem Soc 2018; 140:14777-14788. [PMID: 30208274 DOI: 10.1021/jacs.8b08254] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
A multitechnique spectroscopic and theoretical study of the Cp2M(benzenedithiolato) (M = Ti, V, Mo; Cp = η5-C5H5) series provides deep insight into dithiolene electronic structure contributions to electron transfer reactivity and reduction potential modulation in pyranopterin molybdenum enzymes. This work explains the magnitude of the dithiolene folding distortion and the concomitant changes in metal-ligand covalency that are sensitive to electronic structure changes as a function of d-electron occupancy in the redox orbital. It is shown that the large fold angle differences correlate with covalency, and the fold angle distortion is due to a pseudo-Jahn-Teller (PJT) effect. The PJT effect in these and related transition metal dithiolene systems arises from the small energy differences between metal and sulfur valence molecular orbitals, which uniquely poise these systems for dramatic geometric and electronic structure changes as the oxidation state changes. Herein, we have used a combination of resonance Raman, magnetic circular dichroism, electron paramagnetic resonance, and UV photoelectron spectroscopies to explore the electronic states involved in the vibronic coupling mechanism. Comparison between the UV photoelectron spectroscopy (UPS) of the d2 M = Mo complex and the resonance Raman spectra of the d1 M = V complex reveals the power of this combined spectroscopic approach. Here, we observe that the UPS spectrum of Cp2Mo(bdt) contains an intriguing vibronic progession that is dominated by a "missing-mode" that is composed of PJT-active distortions. We discuss the relationship of the PJT distortions to facile electron transfer in molybdenum enzymes.
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Affiliation(s)
- Benjamin W Stein
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States.,Chemistry Division , Los Alamos National Laboratory , Los Alamos , New Mexico 87545 , United States
| | - Jing Yang
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States
| | - Regina Mtei
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States
| | - Nicholas J Wiebelhaus
- Department of Chemistry and Biochemistry , The University of Arizona , 1306 E. University Boulevard , Tucson , Arizona 85721 , United States
| | - Dominic K Kersi
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States
| | - Jesse LePluart
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States
| | - Dennis L Lichtenberger
- Department of Chemistry and Biochemistry , The University of Arizona , 1306 E. University Boulevard , Tucson , Arizona 85721 , United States
| | - John H Enemark
- Department of Chemistry and Biochemistry , The University of Arizona , 1306 E. University Boulevard , Tucson , Arizona 85721 , United States
| | - Martin L Kirk
- Department of Chemistry and Chemical Biology , The University of New Mexico , MSC 032060, 1 University of New Mexico , Albuquerque , New Mexico 87131 , United States
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9
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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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10
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Pisk J, Bilić L, Đaković M, Cvijanović D, Damjanović V, Lovrić J, Rubčić M, Vrdoljak V, Cindrić M. Design of mononuclear, binuclear and polynuclear molybdenum(VI) complexes based on ONO benzoylacetone derived enaminones and their in vitro biological activity. Polyhedron 2018. [DOI: 10.1016/j.poly.2018.02.003] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Dong C, Yang J, Reschke S, Leimkühler S, Kirk ML. Vibrational Probes of Molybdenum Cofactor-Protein Interactions in Xanthine Dehydrogenase. Inorg Chem 2017; 56:6830-6837. [PMID: 28590138 DOI: 10.1021/acs.inorgchem.7b00028] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The pyranopterin dithiolene (PDT) ligand is an integral component of the molybdenum cofactor (Moco) found in all molybdoenzymes with the sole exception of nitrogenase. However, the roles of the PDT in catalysis are still unknown. The PDT is believed to be bound to the proteins by an extensive hydrogen-bonding network, and it has been suggested that these interactions may function to fine-tune Moco for electron- and atom-transfer reactivity in catalysis. Here, we use resonance Raman (rR) spectroscopy to probe Moco-protein interactions using heavy-atom congeners of lumazine, molecules that bind tightly to both wild-type xanthine dehydrogenase (wt-XDH) and its Q102G and Q197A variants following enzymatic hydroxylation to the corresponding violapterin product molecules. The resulting enzyme-product complexes possess intense near-IR absorption, allowing high-quality rR spectra to be collected on wt-XDH and the Q102G and Q197A variants. Small negative frequency shifts relative to wt-XDH are observed for the low-frequency Moco vibrations. These results are interpreted in the context of weak hydrogen-bonding and/or electrostatic interactions between Q102 and the -NH2 terminus of the PDT, and between Q197 and the terminal oxo of the Mo≡O group. The Q102A, Q102G, Q197A, and Q197E variants do not appreciably affect the kinetic parameters kred and kred/KD, indicating that a primary role for these glutamine residues is to stabilize and coordinate Moco in the active site of XO family enzymes but to not directly affect the catalytic throughput. Raman frequency shifts between wt-XDH and its Q102G variant suggest that the changes in the electron density at the Mo ion that accompany Mo oxidation during electron-transfer regeneration of the catalytically competent active site are manifest in distortions at the distant PDT amino terminus. This implies a primary role for the PDT as a conduit for facilitating enzymatic electron-transfer reactivity in xanthine oxidase family enzymes.
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Affiliation(s)
- Chao Dong
- 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
| | - Stefan Reschke
- Institute of Biochemistry and Biology, Department of Molecular Enzymology, University of Potsdam , 14476 Potsdam, Germany
| | - Silke Leimkühler
- Institute of Biochemistry and Biology, Department of Molecular Enzymology, University of Potsdam , 14476 Potsdam, Germany
| | - 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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12
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Sproules S, Eagle AA, George GN, White JM, Young CG. Mononuclear Sulfido-Tungsten(V) Complexes: Completing the Tp*MEXY (M = Mo, W; E = O, S) Series. Inorg Chem 2017; 56:5189-5202. [DOI: 10.1021/acs.inorgchem.7b00331] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Stephen Sproules
- WestCHEM, School of Chemistry, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Aston A. Eagle
- School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Graham N. George
- Department of Geological Sciences, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E2, Canada
| | - Jonathan M. White
- School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia
- Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Charles G. Young
- Department of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne, Victoria 3086, Australia
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13
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Saeednia S, Iranmanesh P, Ardakani MH, Ebadinejad N. Sonochemical and solvothermal synthesis of methanol {2-[(2-hydroxy-1,1-dimethyl-ethylimino)-methyl]phenolato}-dioxidomolybdenum(VI) complex and its decomposition to MoO3 nanoparticles. J STRUCT CHEM+ 2016. [DOI: 10.1134/s0022476616050188] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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14
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Affiliation(s)
- Charles G. Young
- Department of Chemistry and PhysicsLa Trobe Institute for Molecular ScienceLa Trobe University3086MelbourneVictoriaAustralia
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15
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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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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: 186] [Impact Index Per Article: 18.6] [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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17
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Dong C, Yang J, Leimkühler S, Kirk ML. Pyranopterin dithiolene distortions relevant to electron transfer in xanthine oxidase/dehydrogenase. Inorg Chem 2014; 53:7077-9. [PMID: 24979205 PMCID: PMC4215880 DOI: 10.1021/ic500873y] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The reducing substrates 4-thiolumazine and 2,4-dithiolumazine have been used to form Mo(IV)-product complexes with xanthine oxidase (XO) and xanthine dehydrogenase. These Mo(IV)-product complexes display an intense metal-to-ligand charge-transfer (MLCT) band in the near-infrared region of the spectrum. Optical pumping into this MLCT band yields resonance Raman spectra of the Mo site that are devoid of contributions from the highly absorbing FAD and 2Fe2S clusters in the protein. The resonance Raman spectra reveal in-plane bending modes of the bound product and low-frequency molybdenum dithiolene and pyranopterin dithiolene vibrational modes. This work provides keen insight into the role of the pyranopterin dithiolene in electron-transfer reactivity.
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Affiliation(s)
- Chao Dong
- 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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18
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Alghool S, Slebodnick C. Supramolecular structures of mononuclear and dinuclear dioxomolybdenum(VI) complexes via hydrogen bonds and π–π stacking, thermal studies and electrochemical measurements. Polyhedron 2014. [DOI: 10.1016/j.poly.2013.08.059] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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19
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Zhu RM, Hu L, Li YZ, Song Y, Zuo JL. Syntheses, crystal structures and properties of dinuclear hydrido-tris(3,5-diphenylpyrazol-1-yl)borate complexes with the S―S coupled and dimerized quinoxaline-2,3-dithiolate ligand. INORG CHEM COMMUN 2013. [DOI: 10.1016/j.inoche.2013.05.021] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
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20
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Barry BM, Stein BW, Larsen CA, Wirtz MN, Geiger WE, Waterman R, Kemp RA. Metal Complexes (M = Zn, Sn, and Pb) of 2-Phosphinobenzenethiolates: Insights into Ligand Folding and Hemilability. Inorg Chem 2013; 52:9875-84. [DOI: 10.1021/ic400990n] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Brian M. Barry
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United
States
| | - Benjamin W. Stein
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United
States
| | - Christopher A. Larsen
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United
States
| | - Melissa N. Wirtz
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United
States
| | - William E. Geiger
- Department of Chemistry, University of Vermont, Burlington, Vermont 05405, United
States
| | - Rory Waterman
- Department of Chemistry, University of Vermont, Burlington, Vermont 05405, United
States
| | - Richard A. Kemp
- Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United
States
- Advanced Materials
Laboratory, Sandia National Laboratories, Albuquerque, New Mexico 87106, United States
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21
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Williams BR, Fu Y, Yap GPA, Burgmayer SJN. Structure and reversible pyran formation in molybdenum pyranopterin dithiolene models of the molybdenum cofactor. J Am Chem Soc 2012; 134:19584-7. [PMID: 23157708 DOI: 10.1021/ja310018e] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The syntheses and X-ray structures of two molybdenum pyranopterin dithiolene complexes in biologically relevant Mo(4+) and Mo(5+) states are reported. Crystallography reveals that these complexes possess a pyran ring formed through a spontaneous cyclization reaction of a dithiolene side-chain hydroxyl group at a C═N bond of the pterin. NMR data on the Mo(4+) complex suggest that a reversible pyran ring cyclization occurs in solution. These results provide experimental evidence that the pyranopterin dithiolene ligand in molybdenum and tungsten enzymes could participate in catalysis through dynamic processes modulated by the protein.
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Affiliation(s)
- Benjamin R Williams
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010-2899, United States
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22
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Pasayat S, Dash SP, Saswati, Majhi PK, Patil YP, Nethaji M, Dash HR, Das S, Dinda R. Mixed-ligand aroylhydrazone complexes of molybdenum: Synthesis, structure and biological activity. Polyhedron 2012. [DOI: 10.1016/j.poly.2012.03.007] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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23
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Matsushita O, Derkacheva VM, Muranaka A, Shimizu S, Uchiyama M, Luk’yanets EA, Kobayashi N. Rectangular-Shaped Expanded Phthalocyanines with Two Central Metal Atoms. J Am Chem Soc 2012; 134:3411-8. [DOI: 10.1021/ja209589x] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Osamu Matsushita
- Department of Chemistry, Graduate
School of Science, Tohoku University, Sendai
980-8578, Japan
| | | | - Atsuya Muranaka
- Advanced Elements
Chemistry Research
Team, ASI, RIKEN, Wako 351-0198, Japan
- PRESTO, Japan Science and Technology Agency (JST), Saitama 332-0012, Japan
| | - Soji Shimizu
- Department of Chemistry, Graduate
School of Science, Tohoku University, Sendai
980-8578, Japan
| | - Masanobu Uchiyama
- Advanced Elements
Chemistry Research
Team, ASI, RIKEN, Wako 351-0198, Japan
- Graduate School of Pharmaceutical
Sciences, The University of Tokyo, Bunkyo-ku,
Tokyo 113-0033, Japan
| | - Evgeny A. Luk’yanets
- Organic Intermediates and Dyes Institute, B. Sadovaya 1/4, Moscow 123995,
Russia
| | - Nagao Kobayashi
- Department of Chemistry, Graduate
School of Science, Tohoku University, Sendai
980-8578, Japan
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24
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Yan Y, Chandrasekaran P, Mague JT, DeBeer S, Sproules S, Donahue JP. Redox-Controlled Interconversion between Trigonal Prismatic and Octahedral Geometries in a Monodithiolene Tetracarbonyl Complex of Tungsten. Inorg Chem 2011; 51:346-61. [DOI: 10.1021/ic201748v] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yong Yan
- Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans,
Louisiana 70118-5698, United States
| | - Perumalreddy Chandrasekaran
- Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans,
Louisiana 70118-5698, United States
- Department of Chemistry and
Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
| | - Joel T. Mague
- Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans,
Louisiana 70118-5698, United States
| | - Serena DeBeer
- Department of Chemistry and
Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36,
D-45470 Mülheim an der Ruhr, Germany
| | - Stephen Sproules
- Max-Planck-Institut für Bioanorganische Chemie, Stiftstrasse 34-36,
D-45470 Mülheim an der Ruhr, Germany
- EPSRC National UK EPR Facility
and Service, Photon Science Institute, The University of Manchester, Oxford Road, Manchester M13 9PL, U.K
| | - James P. Donahue
- Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans,
Louisiana 70118-5698, United States
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25
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Mtei RP, Perera E, Mogesa B, Stein B, Basu P, Kirk ML. A Valence Bond Description of Dizwitterionic Dithiolene Character in an Oxomolybdenum-bis(dithione). Eur J Inorg Chem 2011; 2011:5467-5470. [PMID: 23956683 DOI: 10.1002/ejic.201101084] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Metallo-dithiolene non-innocence is explored in an oxomolybdenum-bis(dithione) complex, [Mo4+O(i-Pr2Pipdt)2Cl][PF6] (where i-Pr2Pipdt is N,N'-piperazine-2,3-dithione), that possesses a piperazine ring as an integral part of the dithiolene ligand. The title complex displays unusual spectroscopic features for a formally reduced Mo(IV) dithiolene complex, namely a low energy metal-to-ligand charge transfer band with appreciable intensity and C-C and C-S stretching frequencies that are markedly different from those of oxomolydenum complexes coordinated to dianionic dithiolene ligands. The electronic structure of the ligand has been described in valence bond terms as a resonance hybrid of dithione and dizwitterionic dithiolene contributing structures.
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Affiliation(s)
- Regina P Mtei
- Department of Chemistry and Chemical Biology, The Univesity of New Mexico, MSC03 2060. 1 University of New Mexico, Albuquerque, NM 87131-0001
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26
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Matz KG, Mte RP, Rothstein R, Kirk ML, Nieter Burgmayer SJ. Study of molybdenum(4+) quinoxalyldithiolenes as models for the noninnocent pyranopterin in the molybdenum cofactor. Inorg Chem 2011; 50:9804-15. [PMID: 21894968 PMCID: PMC3268461 DOI: 10.1021/ic200783a] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A model system for the molybdenum cofactor has been developed that illustrates the noninnocent behavior of an N-heterocycle appended to a dithiolene chelate on molybdenum. The pyranopterin of the molybdenum cofactor is modeled by a quinoxalyldithiolene ligand (S(2)BMOQO) formed from the reaction of molybdenum tetrasulfide and quinoxalylalkyne. The resulting complexes TEA[Tp*MoX(S(2)BMOQO)] [1, X = S; 3, X = O; TEA = tetraethylammonium; Tp* = hydrotris(3,5-dimethylpyrazolyl)borate] undergo a dehydration-driven intramolecular cyclization within quinoxalyldithiolene, forming Tp*MoX(pyrrolo-S(2)BMOQO) (2, X = S; 4, X = O). 4 can be oxidized by one electron to produce the molybdenum(5+) complex 5. In a preliminary report of this work, evidence from X-ray crystallography, electronic absorption and resonance Raman spectroscopies, and density functional theory (DFT) bonding calculations revealed that 4 possesses an unusual asymmetric dithiolene chelate with significant thione-thiolate character. The results described here provide a detailed description of the reaction conditions that lead to the formation of 4. Data from cyclic voltammetry, additional DFT calculations, and several spectroscopic methods (IR, electronic absorption, resonance Raman, and electron paramagnetic resonance) have been used to characterize the properties of members in this suite of five Mo(S(2)BMOQO) complexes and further substantiate the highly electron-withdrawing character of the pyrrolo-S(2)BMOQO ligand in 2, 4, and 5. This study of the unique noninnocent ligand S(2)BMOQO provides examples of the roles that the N-heterocycle pterin can play as an essential part of the molybdenum cofactor. The versatile nature of a dithiolene appended by heterocycles may aid in modulating the redox processes of the molybdenum center during the course of enzyme catalysis.
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Affiliation(s)
- Kelly G. Matz
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010
| | - Regina P. Mte
- Department of Chemistry and Chemical Biology, The University of New Mexico, Albuquerque, New Mexico 87131-0001
| | - Rebecca Rothstein
- Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010
| | - Martin L. Kirk
- Department of Chemistry and Chemical Biology, The University of New Mexico, Albuquerque, New Mexico 87131-0001
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27
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Sempombe J, Stein B, Kirk ML. Spectroscopic and electronic structure studies probing covalency contributions to C-H bond activation and transition-state stabilization in xanthine oxidase. Inorg Chem 2011; 50:10919-28. [PMID: 21972782 DOI: 10.1021/ic201477n] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A detailed electron paramagnetic resonance (EPR) and computational study of a key paramagnetic form of xanthine oxidase (XO) has been performed and serves as a basis for developing a valence-bond description of C-H activation and transition-state (TS) stabilization along the reaction coordinate with aldehyde substrates. EPR spectra of aldehyde-inhibited XO have been analyzed in order to provide information regarding the relationship between the g, (95,97)Mo hyperfine (A(Mo)), and (13)C hyperfine (A(C)) tensors. Analysis of the EPR spectra has allowed for greater insight into the electronic origin of key delocalizations within the Mo-O(eq)-C fragment and how these contribute to C-H bond activation/cleavage and TS stabilization. A natural bond orbital analysis of the enzyme reaction coordinate with aldehyde substrates shows that both Mo═S π → C-H σ* (ΔE = 24.3 kcal mol(-1)) and C-H σ → Mo═S π* (ΔE = 20.0 kcal mol(-1)) back-donation are important in activating the substrate C-H bond for cleavage. Additional contributions to C-H activation derive from O(eq) lp → C-H σ* (lp = lone pair; ΔE = 8.2 kcal mol(-1)) and S lp → C-H σ* (ΔE = 13.2 kcal mol(-1)) stabilizing interactions. The O(eq)-donor ligand that derives from water is part of the Mo-O(eq)-C fragment probed in the EPR spectra of inhibited XO, and the observation of O(eq) lp → C-H σ* back-donation indicates a key role for O(eq) in activating the substrate C-H bond for cleavage. We also show that the O(eq) donor plays an even more important role in TS stabilization. We find that O(eq) → Mo + C charge transfer dominantly contributes to stabilization of the TS (ΔE = 89.5 kcal mol(-1)) and the Mo-O(eq)-C delocalization pathway reduces strong electronic repulsions that contribute to the classical TS energy barrier. The Mo-O(eq)-C delocalization at the TS allows for the TS to be described in valence-bond terms as a resonance hybrid of the reactant (R) and product (P) valence-bond wave functions.
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Affiliation(s)
- Joseph Sempombe
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
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28
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Mtei RP, Lyashenko G, Stein B, Rubie N, Hille R, Kirk ML. Spectroscopic and electronic structure studies of a dimethyl sulfoxide reductase catalytic intermediate: implications for electron- and atom-transfer reactivity. J Am Chem Soc 2011; 133:9762-74. [PMID: 21648481 PMCID: PMC3142581 DOI: 10.1021/ja109178q] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The electronic structure of a genuine paramagnetic des-oxo Mo(V) catalytic intermediate in the reaction of dimethyl sulfoxide reductase (DMSOR) with (CH(3))(3)NO has been probed by electron paramagnetic resonance (EPR), electronic absorption, and magnetic circular dichroism (MCD) spectroscopies. EPR spectroscopy reveals rhombic g- and A-tensors that indicate a low-symmetry geometry for this intermediate and a singly occupied molecular orbital that is dominantly metal centered. The excited-state spectroscopic data were interpreted in the context of electronic structure calculations, and this has resulted in a full assignment of the observed MCD and electronic absorption bands, a detailed understanding of the metal-ligand bonding scheme, and an evaluation of the Mo(V) coordination geometry and Mo(V)-S(dithiolene) covalency as it pertains to the stability of the intermediate and electron-transfer regeneration. Finally, the relationship between des-oxo Mo(V) and des-oxo Mo(IV) geometric and electronic structures is discussed relative to the reaction coordinate in members of the DMSOR enzyme family.
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Affiliation(s)
- Regina P Mtei
- Department of Chemistry and Chemical Biology, The University of New Mexico, MSC03 2060, 1 University of New Mexico, Albuquerque, New Mexico 87131-0001, USA
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29
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Sproules S, Eagle AA, Taylor MK, Gable RW, White JM, Young CG. Paramagnetic Oxotungsten(V) Complexes Containing the Hydrotris(3,5-dimethylpyrazol-1-yl)borate Ligand. Inorg Chem 2011; 50:4503-14. [DOI: 10.1021/ic200161m] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Affiliation(s)
- Stephen Sproules
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Aston A. Eagle
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Michelle K. Taylor
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Robert W. Gable
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Jonathan M. White
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
| | - Charles G. Young
- School of Chemistry and §Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Victoria 3010, Australia
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30
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31
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Matz KG, Mtei RP, Leung B, Burgmayer SJN, Kirk ML. Noninnocent dithiolene ligands: a new oxomolybdenum complex possessing a donor-acceptor dithiolene ligand. J Am Chem Soc 2010; 132:7830-1. [PMID: 20481628 DOI: 10.1021/ja100220x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
A new monoanionic dithiolene ligand is found in Tp*MoO(S(2)BMOQO). A combination of X-ray crystallography, electronic absorption spectroscopy, resonance Raman spectroscopy, and bonding calculations reveal that the monoanionic dithiolene ligand possesses considerable thiolate-thione character resulting from an admixture of an intraligand charge transfer excited state into the ground state wave function. The unusual dithiolene exhibits a highly versatile donor-acceptor character that dramatically affects the Mo(IV/V) redox couple and points to a potentially noninnocent role of the pterin fragment in pyranopterin Mo enzymes.
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Affiliation(s)
- Kelly G Matz
- Department of Chemistry, Bryn Mawr College, 101 North Merion Avenue, Bryn Mawr, Pennsylvania 19010-2899, USA
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32
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Yang J, Rothery R, Sempombe J, Weiner JH, Kirk ML. Spectroscopic characterization of YedY: the role of sulfur coordination in a Mo(V) sulfite oxidase family enzyme form. J Am Chem Soc 2010; 131:15612-4. [PMID: 19860477 DOI: 10.1021/ja903087k] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Electronic paramagnetic resonance (EPR), electronic absorption, and magnetic circular dichroism spectroscopies have been performed on YedY, a SUOX fold protein with a Mo domain that is remarkably similar to that found in chicken sulfite oxidase, Arabidopsis thaliana plant sulfite oxidase, and the bacterial sulfite dehydrogenase from Starkeya novella. Low-energy dithiolene --> Mo and cysteine thiolate --> Mo charge-transfer bands have been assigned for the first time in a Mo(V) form of a SUOX fold protein, and the spectroscopic data have been used to interpret the results of bonding calculations. The analysis shows that second coordination sphere effects modulate dithiolene and cysteine sulfur covalency contributions to the Mo bonding scheme. In particular, a more acute O(oxo)-Mo-S(Cys)-C dihedral angle results in increased cysteine thiolate S --> Mo charge transfer and a large g(1) in the EPR spectrum. The spectrosocopic results, coupled with the available structural data, indicate that these second coordination sphere effects may play key roles in modulating the active-site redox potential, facilitating hole superexchange pathways for electron transfer regeneration, and affecting the type of reactions catalyzed by sulfite oxidase family enzymes.
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Affiliation(s)
- Jing Yang
- Department of Chemistry and Chemical Biology, The University of New Mexico, Albuquerque, New Mexico 87131, USA
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33
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Cindrić M, Galin G, Matković-Čalogović D, Novak P, Hrenar T, Ljubić I, Novak TK. Synthesis and characterization of three novel molybdenum(VI) complexes: Mononuclear [MoO2(C6H4(O)CHNCH(COO)CH2C(O)NH2)], [MoO2(C19H19N2O5)(CH3OH)]Cl·CH3OH and dinuclear [Mo2O4(C6H4(O)CHNCH(COO)CH2C(O)NH2)2]. Polyhedron 2009. [DOI: 10.1016/j.poly.2008.11.058] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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34
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Tenderholt AL, Szilagyi RK, Holm RH, Hodgson KO, Hedman B, Solomon EI. Electronic control of the "Bailar twist" in formally d0-d2 molybdenum tris(dithiolene) complexes: a sulfur K-edge X-ray absorption spectroscopy and density functional theory study. Inorg Chem 2008; 47:6382-92. [PMID: 18517189 DOI: 10.1021/ic800494h] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Sulfur K-edge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations have been used to determine the electronic structures of a series of Mo tris(dithiolene) complexes, [Mo(mdt)3](z) (where mdt = 1,2-dimethylethene-1,2-dithiolate(2-) and z = 2-, 1-, 0), with near trigonal-prismatic geometries (D3h symmetry). These results show that the formally Mo(IV), Mo(V), and Mo(VI) complexes actually have a (dz(2))(2) configuration, that is, remain effectively Mo(IV) despite oxidation. Comparisons with the XAS data of another set of Mo tris(dithiolene) complexes, [Mo(tbbdt)3](z) (where tbbdt = 3,5-ditert-butylbenzene-1,2-dithiolate(2-) and z = 1-, 0), show that both neutral complexes, [Mo(mdt)3] and [Mo(tbbdt)3], have similar electronic structures while the monoanions do not. Calculations reveal that the "Bailar twist" present in the crystal structure of [Mo(tbbdt)3](1-) (D3 symmetry) but not [Mo(mdt)3](1-) (D3h symmetry) is controlled by electronic factors which arise from bonding differences between the mdt and tbbdt ligands. In the former, configuration interaction between the Mo d(z(2)) and a deeper energy, occupied ligand orbital, which occurs in D3 symmetry, destabilizes the Mo d(z(2)) to above another ligand orbital which is half-occupied in the D3h [Mo(mdt)3](1-) complex. This leads to a metal d(1) configuration with no ligand holes (i.e., d(1)[L3](0h)) for [Mo(tbbdt)3](1-) rather than the metal d(2) configuration with one ligand hole (i.e., d(2)[L3](1h)) for [Mo(mdt)3](1-). Thus, the Bailar twist observed in some metal tris(dithiolene) complexes is the result of configuration interaction between metal and ligand orbitals and can be probed experimentally by S K-edge XAS.
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Affiliation(s)
- Adam L Tenderholt
- Department of Chemistry, Stanford University, Stanford, California 94305, USA
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35
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McNaughton RL, Lim BS, Knottenbelt SZ, Holm RH, Kirk ML. Spectroscopic and electronic structure studies of symmetrized models for reduced members of the dimethylsulfoxide reductase enzyme family. J Am Chem Soc 2008; 130:4628-36. [PMID: 18341333 DOI: 10.1021/ja074691b] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Enzymes belonging to the dimethylsulfoxide reductase (DMSOR) family of pyranopterin Mo enzymes have a unique active-site geometry in the reduced form that lacks a terminal oxo ligand, unlike the reduced active sites of other pyranopterin Mo enzymes. Furthermore, the DMSOR family is characterized by the coordination of two pyranopterin-ene-1,2-dithiolate ligands in their active sites, which is distinctive among the other pyranopterin Mo enzymes but analogous to all of the currently known tungsten-containing enzymes. Electronic absorption, resonance Raman, and ground- and excited-state density functional calculations of symmetrized analogues of the reduced DMSOR active site ([NEt4][Mo(IV)(QAd)(S2C2Me2)2] where Ad = 2-adamantyl; Q = O, S, Se) have allowed for a detailed description of Mo-bisdithiolene electronic structure in the absence of a strong-field oxo ligand. The electronic absorption spectra are dominated by dithiolene S --> Mo charge-transfer transitions, and the totally symmetric Mo-S Raman stretch is observed at approximately 400 cm(-1) for all three complexes. These data indicate that the Mo-bisdithiolene bonding scheme in high-symmetry [Mo(QAd)(S2C2Me2)2]- complexes is not strongly perturbed by the apical QAd- ligands, but instead, the dithiolene ligands define the t(2g) ligand field splitting. The effects of conserved geometric distortions observed in DMSOR, relative to these high-symmetry models, were explored by spectroscopically calibrated bonding calculations, and the results are discussed within the context of electronic structure contributions to ground-state destabilization and transition-state stabilization. The specific electronic structure tuning of the endogenous amino acid ligation on the mechanism of DMSOR is also discussed.
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Affiliation(s)
- Rebecca L McNaughton
- Department of Chemistry, The University of New Mexico, MSC03 2060, Albuquerque, New Mexico 87131, USA
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