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Martin L. Kirk - One of the best experts on this subject based on the ideXlab platform.
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Molybdenum and Tungsten Cofactors and the Reactions They Catalyze.
Metal ions in life sciences, 2020Co-Authors: Martin L. KirkAbstract:The last 20 years have seen a dramatic increase in our mechanistic understanding of the reactions catalyzed by Pyranopterin Mo and W enzymes. These enzymes possess a unique cofactor (Moco) that contains a novel ligand in bioinorganic chemistry, the Pyranopterin ene-1,2-dithiolate. A synopsis of Moco biosynthesis and structure is presented, along with our current understanding of the role Moco plays in enzymatic catalysis. Oxygen atom transfer (OAT) reactivity is discussed in terms of breaking strong metal-oxo bonds and the mechanism of OAT catalyzed by enzymes of the sulfite oxidase (SO) family that possess dioxo Mo(VI) active sites. OAT reactivity is also discussed in members of the dimethyl sulfoxide (DMSO) reductase family, which possess des-oxo Mo(IV) sites. Finally, we reveal what is known about hydride transfer reactivity in xanthine oxidase (XO) family enzymes and the formate dehydrogenases. The formal hydride transfer reactivity catalyzed by xanthine oxidase family enzymes is complex and cleaves substrate C-H bonds using a mechanism that is distinct from monooxygenases. The chapter primarily highlights developments in the field that have occurred since ~2000, which have contributed to our collective structural and mechanistic understanding of the three canonical Pyranopterin Mo enzymes families: XO, SO, and DMSO reductase.
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Metal–Dithiolene Bonding Contributions to Pyranopterin Molybdenum Enzyme Reactivity
Inorganics, 2020Co-Authors: Jing Yang, John H. Enemark, Martin L. KirkAbstract: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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metal dithiolene bonding contributions to Pyranopterin molybdenum enzyme reactivity
Inorganics, 2020Co-Authors: Jing Yang, John H. Enemark, Martin L. KirkAbstract: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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The Role of the Pyranopterin Dithiolene Component of Moco in Molybdoenzyme Catalysis
Structure and Bonding, 2019Co-Authors: Sharon J. Nieter Burgmayer, Martin L. KirkAbstract:An overview of the Pyranopterin dithiolene (MPT) component of the molybdenum cofactor (Moco) and how MPT may contribute to enzymatic catalysis is presented. The chapter begins with a brief review of MPT and Moco biosynthesis and continues to explore the nature of what is arguably the most electronically complex ligand in biology. To explore this complexity, we have dissected MPT into its relevant molecular components. These include the redox-active ene-1,2-dithiolate (dithiolene) and pterin moieties, which are bridged by a pyran that may be found in ring-opened or ring-closed configurations. The various redox possibilities of MPT bound to Mo are presented, along with the electronic structure of the redox components. MPTs are found to display a remarkable conformational variance in Pyranopterin Mo enzymes. This is discussed in terms of a relationship to enzyme function and the potential for the observed non-planer distortions to reflect different MPT oxidation and tautomeric states. The chapter ends with a series of case studies featuring model compounds that highlight how biomimetic small molecule studies have contributed to furthering our understanding of the roles this remarkable ligand plays in the catalytic cycles of the enzymes.
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implications of pyran cyclization and pterin conformation on oxidized forms of the molybdenum cofactor
Journal of the American Chemical Society, 2018Co-Authors: Douglas R. Gisewhite, Benjamin W Stein, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Sharon Nieter J. BurgmayerAbstract: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 t...
Sharon J. Nieter Burgmayer - One of the best experts on this subject based on the ideXlab platform.
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The Role of the Pyranopterin Dithiolene Component of Moco in Molybdoenzyme Catalysis
Structure and Bonding, 2019Co-Authors: Sharon J. Nieter Burgmayer, Martin L. KirkAbstract:An overview of the Pyranopterin dithiolene (MPT) component of the molybdenum cofactor (Moco) and how MPT may contribute to enzymatic catalysis is presented. The chapter begins with a brief review of MPT and Moco biosynthesis and continues to explore the nature of what is arguably the most electronically complex ligand in biology. To explore this complexity, we have dissected MPT into its relevant molecular components. These include the redox-active ene-1,2-dithiolate (dithiolene) and pterin moieties, which are bridged by a pyran that may be found in ring-opened or ring-closed configurations. The various redox possibilities of MPT bound to Mo are presented, along with the electronic structure of the redox components. MPTs are found to display a remarkable conformational variance in Pyranopterin Mo enzymes. This is discussed in terms of a relationship to enzyme function and the potential for the observed non-planer distortions to reflect different MPT oxidation and tautomeric states. The chapter ends with a series of case studies featuring model compounds that highlight how biomimetic small molecule studies have contributed to furthering our understanding of the roles this remarkable ligand plays in the catalytic cycles of the enzymes.
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Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization
Inorganic Chemistry, 2019Co-Authors: Douglas R. Gisewhite, Alexandra L. Nagelski, Daniel C. Cummins, Sharon J. Nieter BurgmayerAbstract: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–dithiol...
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Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl-Dithiolene Promoting Pyran Cyclization.
Inorganic chemistry, 2019Co-Authors: Douglas R. Gisewhite, Alexandra L. Nagelski, Daniel C. Cummins, Glen P. A. Yap, Sharon J. Nieter BurgmayerAbstract: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–dithiol...
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Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor
2018Co-Authors: Douglas R. Gisewhite, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Benjamin Stein, Sharon J. Nieter BurgmayerAbstract: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 MoO 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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CHAPTER 2:Pterin-Inspired Model Compounds of Molybdenum Enzymes
Molybdenum and Tungsten Enzymes, 2016Co-Authors: Sharon J. Nieter Burgmayer, Benjamin R. Williams, Partha BasuAbstract:The molybdenum cofactor at the catalytic heart of mononuclear molybdoenzymes comprises a molybdenum ion coordinated by one or two dithiolene ligands containing an N-heterocyclic structure known as pterin. Understanding the details of the unusual combination of molybdenum with pterin and dithiolene is the impetus behind employing model chemistry to investigate the cofactor’s broad redox capabilities. This chapter highlights the major efforts to synthesize pterin-containing models and study their chemical properties. The history of identification of the cofactor’s Pyranopterin dithiolene ligand and the details of pterin redox chemistry are reviewed, followed by an account of the synthesis and analysis of pterin-inspired chemical models. The implications of these models’ chemical reactivity and redox features that provide a fundamental basis for understanding the molybdenum cofactor are included. In addition, we highlight the potential directions of the field.
Benjamin R. Williams - One of the best experts on this subject based on the ideXlab platform.
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implications of pyran cyclization and pterin conformation on oxidized forms of the molybdenum cofactor
Journal of the American Chemical Society, 2018Co-Authors: Douglas R. Gisewhite, Benjamin W Stein, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Sharon Nieter J. BurgmayerAbstract: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 t...
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Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor
2018Co-Authors: Douglas R. Gisewhite, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Benjamin Stein, Sharon J. Nieter BurgmayerAbstract: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 MoO 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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CHAPTER 2:Pterin-Inspired Model Compounds of Molybdenum Enzymes
Molybdenum and Tungsten Enzymes, 2016Co-Authors: Sharon J. Nieter Burgmayer, Benjamin R. Williams, Partha BasuAbstract:The molybdenum cofactor at the catalytic heart of mononuclear molybdoenzymes comprises a molybdenum ion coordinated by one or two dithiolene ligands containing an N-heterocyclic structure known as pterin. Understanding the details of the unusual combination of molybdenum with pterin and dithiolene is the impetus behind employing model chemistry to investigate the cofactor’s broad redox capabilities. This chapter highlights the major efforts to synthesize pterin-containing models and study their chemical properties. The history of identification of the cofactor’s Pyranopterin dithiolene ligand and the details of pterin redox chemistry are reviewed, followed by an account of the synthesis and analysis of pterin-inspired chemical models. The implications of these models’ chemical reactivity and redox features that provide a fundamental basis for understanding the molybdenum cofactor are included. In addition, we highlight the potential directions of the field.
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Solvent-Dependent Pyranopterin Cyclization in Molybdenum Cofactor Model Complexes.
Inorganic chemistry, 2015Co-Authors: Benjamin R. Williams, Douglas R. Gisewhite, Anna Kalinsky, Alisha Esmail, Sharon J. Nieter BurgmayerAbstract:The conserved pterin dithiolene ligand that coordinates molybdenum (Mo) in the cofactor (Moco) of mononuclear Mo enzymes can exist in both a tricyclic Pyranopterin dithiolene form and as a bicyclic...
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Solvent-Dependent Pyranopterin Cyclization in Molybdenum Cofactor Model Complexes
2015Co-Authors: Benjamin R. Williams, Anna Kalinsky, Alisha Esmail, Douglas Gisewhite, Sharon Nieter J. BurgmayerAbstract:The conserved pterin dithiolene ligand that coordinates molybdenum (Mo) in the cofactor (Moco) of mononuclear Mo enzymes can exist in both a tricyclic Pyranopterin dithiolene form and as a bicyclic pterin–dithiolene form as observed in protein crystal structures of several bacterial molybdoenzymes. Interconversion between the tricyclic and bicyclic forms via pyran scission and cyclization has been hypothesized to play a role in the catalytic mechanism of Moco. Therefore, understanding the interconversion between the tricyclic and bicyclic forms, a type of ring–chain tautomerism, is an important aspect of study to understand its role in catalysis. In this study, equilibrium constants (Keq) as well as enthalpy, entropy, and free energy values are obtained for pyran ring tautomerism exhibited by two Moco model complexes, namely, (Et4N)[Tp*Mo(O)(S2BMOPP)] (1) and (Et4N)[Tp*Mo(O)(S2PEOPP)] (2), as a solvent-dependent equilibrium process. Keq values obtained from 1H NMR data in seven deuterated solvents show a correlation between solvent polarity and tautomer form, where solvents with higher polarity parameters favor the pyran form
Douglas R. Gisewhite - One of the best experts on this subject based on the ideXlab platform.
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Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl–Dithiolene Promoting Pyran Cyclization
Inorganic Chemistry, 2019Co-Authors: Douglas R. Gisewhite, Alexandra L. Nagelski, Daniel C. Cummins, Sharon J. Nieter BurgmayerAbstract: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–dithiol...
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Modeling Pyran Formation in the Molybdenum Cofactor: Protonation of Quinoxalyl-Dithiolene Promoting Pyran Cyclization.
Inorganic chemistry, 2019Co-Authors: Douglas R. Gisewhite, Alexandra L. Nagelski, Daniel C. Cummins, Glen P. A. Yap, Sharon J. Nieter BurgmayerAbstract: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–dithiol...
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implications of pyran cyclization and pterin conformation on oxidized forms of the molybdenum cofactor
Journal of the American Chemical Society, 2018Co-Authors: Douglas R. Gisewhite, Benjamin W Stein, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Sharon Nieter J. BurgmayerAbstract: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 t...
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Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor
2018Co-Authors: Douglas R. Gisewhite, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Benjamin Stein, Sharon J. Nieter BurgmayerAbstract: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 MoO 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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Solvent-Dependent Pyranopterin Cyclization in Molybdenum Cofactor Model Complexes.
Inorganic chemistry, 2015Co-Authors: Benjamin R. Williams, Douglas R. Gisewhite, Anna Kalinsky, Alisha Esmail, Sharon J. Nieter BurgmayerAbstract:The conserved pterin dithiolene ligand that coordinates molybdenum (Mo) in the cofactor (Moco) of mononuclear Mo enzymes can exist in both a tricyclic Pyranopterin dithiolene form and as a bicyclic...
Jing Yang - One of the best experts on this subject based on the ideXlab platform.
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Metal–Dithiolene Bonding Contributions to Pyranopterin Molybdenum Enzyme Reactivity
Inorganics, 2020Co-Authors: Jing Yang, John H. Enemark, Martin L. KirkAbstract: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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metal dithiolene bonding contributions to Pyranopterin molybdenum enzyme reactivity
Inorganics, 2020Co-Authors: Jing Yang, John H. Enemark, Martin L. KirkAbstract: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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vibrational control of covalency effects related to the active sites of molybdenum enzymes
Journal of the American Chemical Society, 2018Co-Authors: John H. Enemark, Benjamin W Stein, Regina P Mtei, Nicholas J Wiebelhaus, Dominic K Kersi, Jesse Lepluart, Dennis L. Lichtenberger, Jing Yang, M.l. KirkAbstract: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 ...
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implications of pyran cyclization and pterin conformation on oxidized forms of the molybdenum cofactor
Journal of the American Chemical Society, 2018Co-Authors: Douglas R. Gisewhite, Benjamin W Stein, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Sharon Nieter J. BurgmayerAbstract: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 t...
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Implications of Pyran Cyclization and Pterin Conformation on Oxidized Forms of the Molybdenum Cofactor
2018Co-Authors: Douglas R. Gisewhite, Benjamin R. Williams, Jing Yang, Martin L. Kirk, Alisha Esmail, Benjamin Stein, Sharon J. Nieter BurgmayerAbstract: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 MoO 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
