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Govindasamy Mugesh - One of the best experts on this subject based on the ideXlab platform.

  • Insights into the catalytic mechanism of synthetic glutathione peroxidase mimetics
    Organic and Biomolecular Chemistry, 2015
    Co-Authors: Debasish Bhowmick, Govindasamy Mugesh
    Abstract:

    Glutathione Peroxidase (GPx) is a key selenoenzyme that protects biomolecules from oxidative damage. Extensive research has been carried out to design and synthesize small organoSelenium compounds as functional mimics of GPx. While the catalytic mechanism of the native enzyme itself is poorly understood, the synthetic mimics follow different catalytic pathways depending upon the structures and reactivities of various intermediates formed in the catalytic cycle. The steric as well as electronic environments around the Selenium Atom not only modulate the reactivity of these synthetic mimics towards peroxides and thiols, but also the catalytic mechanisms. The catalytic cycle of small GPx mimics is also dependent on the nature of peroxides and thiols used in the study. In this review, we discuss how the catalytic mechanism varies with the substituents attached to the Selenium Atom.

  • Insights into the catalytic mechanism of synthetic glutathione peroxidase mimetics
    Organic and Biomolecular Chemistry, 2015
    Co-Authors: Debasish Bhowmick, Govindasamy Mugesh
    Abstract:

    Glutathione Peroxidase (GPx) is a key selenoenzyme that protects biomolecules from oxidative damage. Extensive research has been carried out to design and synthesize small organoSelenium compounds as functional mimics of GPx. While the catalytic mechanism of the native enzyme itself is poorly understood, the synthetic mimics follow different catalytic pathways depending upon the structures and reactivities of various intermediates formed in the catalytic cycle. The steric as well as electronic environments around the Selenium Atom not only modulate the reactivity of these synthetic mimics towards peroxides and thiols, but also the catalytic mechanisms. The catalytic cycle of small GPx mimics is also dependent on the nature of peroxides and thiols used in the study. In this review, we discuss how the catalytic mechanism varies with the substituents attached to the Selenium Atom.

  • thyroid hormone synthesis and anti thyroid drugs a bioinorganic chemistry approach
    Journal of Chemical Sciences, 2006
    Co-Authors: Govindasamy Mugesh
    Abstract:

    Hydrogen peroxide, generated by thyroid oxidase enzymes, is a crucial substrate for the thyroid peroxidase (TPO)-catalysed biosynthesis of thyroid hormones, thyroxine (T4) and triiodothyronine (T3) in the thyroid gland. It is believed that the H2O2 generation is a limiting step in thyroid hormone synthesis. Therefore, the control of hydrogen peroxide concentration is one of the possible mechanisms for the inhibition of thyroid hormone biosynthesis. The inhibition of thyroid hormone synthesis is required for the treatment of hyperthyroidism and this can be achieved by one or more anti-thyroid drugs. The most widely used anti-thyroid drug methimazole (MMI) inhibits the production of thyroid hormones by irreversibly inactivating the enzyme TPO. Our studies show that the replacement of sulphur in MMI by Selenium leads to a selone, which exists predominantly in its zwitterionic form. In contrast to the sulphur drug, the Selenium analogue (MSeI) reversibly inhibits the peroxidase-catalysed oxidation and iodination reactions. Theoretical studies on MSeI reveal that the Selenium Atom in this compound carries a large negative charge. The carbon-Selenium bond length in MSeI is found to be close to single-bond length. As the Selenium Atom exhibits a large nucleophilic character, the Selenium analogue of MMI may scavenge the hydrogen peroxide present in the thyroid cells, which may lead to a reversible inhibition of thyroid hormone biosynthesis.

Tao Qian - One of the best experts on this subject based on the ideXlab platform.

  • Selenium doped carbon nanosheets with strong electron cloud delocalization for nondeposition of metal oxides on air cathode of zinc air battery
    ACS Applied Materials & Interfaces, 2019
    Co-Authors: Mengfan Wang, Tao Qian
    Abstract:

    The deposition of metal oxides on the air cathode is a well-known problem for metal–air batteries, since it can cover the active surface and block the oxygen gas diffusion pathway, resulting in poor battery performance and serious cell degeneration. Herein, through deliberate Selenium doping in nitrogen-doped carbon, a strong electron cloud delocalization among the carbon matrix is realized, which can prevent the air cathode from zinc oxide poisoning during zinc–air battery operation, as confirmed by experimental results and density functional theory simulations. In situ X-ray powder diffraction observation confirms that the increased electron cloud density of the surrounding carbon caused by electron delocalization from Selenium Atom could repulse the access of zincate ions, effectively prohibiting the oxide deposition on the air cathode. An amazingly long zinc–air battery cycle life reaching 780 cycles is thus obtained.

  • Selenium-Doped Carbon Nanosheets with Strong Electron Cloud Delocalization for Nondeposition of Metal Oxides on Air Cathode of Zinc–Air Battery
    2019
    Co-Authors: Sisi Liu, Mengfan Wang, Tao Qian, Jie Liu, Chenglin Yan
    Abstract:

    The deposition of metal oxides on the air cathode is a well-known problem for metal–air batteries, since it can cover the active surface and block the oxygen gas diffusion pathway, resulting in poor battery performance and serious cell degeneration. Herein, through deliberate Selenium doping in nitrogen-doped carbon, a strong electron cloud delocalization among the carbon matrix is realized, which can prevent the air cathode from zinc oxide poisoning during zinc–air battery operation, as confirmed by experimental results and density functional theory simulations. In situ X-ray powder diffraction observation confirms that the increased electron cloud density of the surrounding carbon caused by electron delocalization from Selenium Atom could repulse the access of zincate ions, effectively prohibiting the oxide deposition on the air cathode. An amazingly long zinc–air battery cycle life reaching 780 cycles is thus obtained

Debasish Bhowmick - One of the best experts on this subject based on the ideXlab platform.

  • Insights into the catalytic mechanism of synthetic glutathione peroxidase mimetics
    Organic and Biomolecular Chemistry, 2015
    Co-Authors: Debasish Bhowmick, Govindasamy Mugesh
    Abstract:

    Glutathione Peroxidase (GPx) is a key selenoenzyme that protects biomolecules from oxidative damage. Extensive research has been carried out to design and synthesize small organoSelenium compounds as functional mimics of GPx. While the catalytic mechanism of the native enzyme itself is poorly understood, the synthetic mimics follow different catalytic pathways depending upon the structures and reactivities of various intermediates formed in the catalytic cycle. The steric as well as electronic environments around the Selenium Atom not only modulate the reactivity of these synthetic mimics towards peroxides and thiols, but also the catalytic mechanisms. The catalytic cycle of small GPx mimics is also dependent on the nature of peroxides and thiols used in the study. In this review, we discuss how the catalytic mechanism varies with the substituents attached to the Selenium Atom.

  • Insights into the catalytic mechanism of synthetic glutathione peroxidase mimetics
    Organic and Biomolecular Chemistry, 2015
    Co-Authors: Debasish Bhowmick, Govindasamy Mugesh
    Abstract:

    Glutathione Peroxidase (GPx) is a key selenoenzyme that protects biomolecules from oxidative damage. Extensive research has been carried out to design and synthesize small organoSelenium compounds as functional mimics of GPx. While the catalytic mechanism of the native enzyme itself is poorly understood, the synthetic mimics follow different catalytic pathways depending upon the structures and reactivities of various intermediates formed in the catalytic cycle. The steric as well as electronic environments around the Selenium Atom not only modulate the reactivity of these synthetic mimics towards peroxides and thiols, but also the catalytic mechanisms. The catalytic cycle of small GPx mimics is also dependent on the nature of peroxides and thiols used in the study. In this review, we discuss how the catalytic mechanism varies with the substituents attached to the Selenium Atom.

L. Keith Woo - One of the best experts on this subject based on the ideXlab platform.

  • Sulfur and Selenium Atom Transfer Reactions of Tin Porphyrins
    Journal of the American Chemical Society, 1995
    Co-Authors: Lisa M. Berreau, L. Keith Woo
    Abstract:

    Treatment of (meso-tetraphenylporphyrinato)tin(IV) sulfide, (TPP)Sn=S, with (meso-tetra-p-tolylporphyrinato )tin(II), (TTP)Sn11, in toluene results in the reversible exchange (K = 1.21 ± 0.03 at -10 °C) of a sulfur ligand to form (TPP)Sn11 and (TTP)Sn=S. The net result is a formal two-electron redox process between Snii and Sn1v. This occurs with a second-order rate constant at 30 °C of 0.40 ± 0.05 M-1 s1 (AH* = 10.9 ± 0.9 kcaVmol, !l.S* = -24.1 ± 2.8 cal(mol·K)1). Similarly, treatment of (meso-tetraphenylporphyrinato)tin(IV) selenide, (TPP)Sn=Se, with (meso-tetra-p-tolylporphyrinato)tin(II), (TTP)Snn, in toluene results in the reversible exchange (K = 1.45 ± 0.13 at -10 oq of a Selenium ligand to form (TPP)Sn11 and (TTP)Sn=Se. This reaction occurs with a second-order rate constant at 30 oc of 87.3 ± 8.06 M1 s1 (Ali* 9.3 ± 0.5 kcaVmol, !l.S* = -18.8 ± 1.5 cal(mol·K)1 ). Discussion of an inner sphere mechanism involving a ,u-sulfido or a ,u-selenido bridged intermediate is presented. The rate ratio of Selenium to sulfur Atom transfer is 218:1 at 30 °C. This rate behavior follows the "normal" trend as observed for the analogous halogen transfer reactions (1> Br> Cl> F-). Atom transfer reactions continue to be an area of fundanlental importance. Numerous studies have focused on oxygen Atom transfer due to its relevance in both biological systems and industrial or laboratory oxidation processes.2•3 While these have provided a large number of examples involving the transfer of an oxygen Atom between a metal center and organic or nonmetal substrates, the related process of intermetal oxygen Atom transfer reactions is still underdeveloped by comparison. The scope of intermetal oxygen Atom transfer has recently been reviewed.4 Relatively few studies have been reported on sulfur or Selenium Atom transfer. Examples involving the transfer of a sulfur or Selenium Atom from a non-metal species (e.g. phosphine chalcogenides or ethylene sulfide) to a low-valent metal center have recently been utilized to prepare novel terminal sulfido and selenido complexes of the early transition metals.5 These reactions are unusual in that phosphines generally remove sulfur from metal complexes due to the strength of the phosphine sulfide bond (s.:92 kcaVmol).6 Intermetal Atom transfer reactions utilizing Cpz TiS5 and Cp2 TiSe5 as chalcogen transfer reagents have provided a synthetic route to new terminal and perchalcogenido species.710 These reactions formally represent a ® Abstract published in Advance A CS Abstracts, January 15, 1995. (1) Presidential Young Investigator, 1990-1995; Camille and Henry Dreyfus Teacher-Scholar 1993-1998. (2) For lead references, see: Ostovic, D.; Bruice, T. Ace. Chern. Res. 1992, 25, 314. (3) (a) Holm, R. H. Chern. Rev. 1987, 87, 1401. (b) Holm, R. H.; Donahue, J. P. Polyhedron 1993, 12, 571. (c) Jorgenson, K. A. Chern. Rev. 1989, 89, 431. (4) Woo, L. K. Chern. Rev. 1993, 93, 1125. (5) (a) Woo, L. K.; Hays, J. A.; Young, V. G., Jr.; Day, C. L.; Caron, C.; D'Souza, F.; Kadish, K. M. Inorg. Chern. 1993, 32, 4186. (b) Hall, K. A.; Mayer, J. M. J. Am. Chern. Soc. 1992, 114, 10402 and references therein. (6) Chernick, C. L.; Pedley, J. B.; Skinner, H. A. J. Chern. Soc. 1957, 1851. (7) Bolinger, C. M.; Hoots, J. E.; Rauchfuss, T. B. Organometallics 1982, 1, 223. (8) (a) Guilard, R.; Ratti, C.; Tabard, A.; Richard, P.; Dubois, D.; Kadish, K. M. lnorg. Chern. 1990, 29,2532. (b) Ratti, C.; Richard, P.; Tabard, A.; Guilard, R. J. Chern. Soc., Chern. Commun. 1989, 69. (9) Guilard, R.; Ratti, C.; Barbe, J.-M.; Dubois, D.; Kadish, K. M. Inorg. Chern. 1991, 30, 1537. (10) Poncet, J. L.; Guilard, R.; Friant, P.; Goulon-Ginet, C.; Goulon J. Nouv. J. Chim. 1984, 8, 583. 0002-7863/95/1517-1314$09.00/0 secondary Atom transfer process3• since reduction of the rP-X5 (X = S, Se) ligand has taken place.4 Metalloporphyrin complexes have been used to investigate a variety of innersphere redox processes involving intermetal halogen, 11 oxygen, 12 and nitrogen Atom transfer reactions. 13•14 We recently reported the discovery of intermetal oxygen, sulfur, and Selenium Atom transfer reactions involving titanium porphyrin complexes (eq 1). 15·16 Equation 1 also represents a secondary Atom transfer process in which X2is reduced to 2xz-.4 (OEP)Ti(X2) + (TTP)Ti(PhC=CPh) (OEP)Ti=X + (TTP)Ti-X + PhC=CPh (1)

  • Intermetal Oxygen, Sulfur, and Selenium Atom Transfer Reactions Involving Titanium Porphyrin Complexes
    Inorganic Chemistry, 1993
    Co-Authors: L. Keith Woo, J. Alan Hays
    Abstract:

    The reaction of (octaethylporphyrinato) titanium (IV) perchalcogenido complexes (OEP)Ti([eta][sup 2]-X[sub 2])(X = O,S,Se) with (tetratolylporphyrinato)titanium(II) acetylene complexes (TTP)Ti([eta][sup 2]-PhC[triple bond]CPh) or (TTP)Ti([eta][sup 2]-EtC[triple bond]CEt) in C[sub 6]D[sub 6] results in oxygen, sulfur, or Selenium Atom transfer processes which produce (TTP)Ti[double bond]X and (OEP)Ti[double bond]X. These reactions are formally two-electron processes in which X-X bond cleavage has occurred and [eta][sup 2]-X[sub 2][sup 2][sup [minus]] is reduced to 2 X[sup 2][sup [minus]] and Ti(II) is oxidized to Ti(IV).

Mengfan Wang - One of the best experts on this subject based on the ideXlab platform.

  • Selenium doped carbon nanosheets with strong electron cloud delocalization for nondeposition of metal oxides on air cathode of zinc air battery
    ACS Applied Materials & Interfaces, 2019
    Co-Authors: Mengfan Wang, Tao Qian
    Abstract:

    The deposition of metal oxides on the air cathode is a well-known problem for metal–air batteries, since it can cover the active surface and block the oxygen gas diffusion pathway, resulting in poor battery performance and serious cell degeneration. Herein, through deliberate Selenium doping in nitrogen-doped carbon, a strong electron cloud delocalization among the carbon matrix is realized, which can prevent the air cathode from zinc oxide poisoning during zinc–air battery operation, as confirmed by experimental results and density functional theory simulations. In situ X-ray powder diffraction observation confirms that the increased electron cloud density of the surrounding carbon caused by electron delocalization from Selenium Atom could repulse the access of zincate ions, effectively prohibiting the oxide deposition on the air cathode. An amazingly long zinc–air battery cycle life reaching 780 cycles is thus obtained.

  • Selenium-Doped Carbon Nanosheets with Strong Electron Cloud Delocalization for Nondeposition of Metal Oxides on Air Cathode of Zinc–Air Battery
    2019
    Co-Authors: Sisi Liu, Mengfan Wang, Tao Qian, Jie Liu, Chenglin Yan
    Abstract:

    The deposition of metal oxides on the air cathode is a well-known problem for metal–air batteries, since it can cover the active surface and block the oxygen gas diffusion pathway, resulting in poor battery performance and serious cell degeneration. Herein, through deliberate Selenium doping in nitrogen-doped carbon, a strong electron cloud delocalization among the carbon matrix is realized, which can prevent the air cathode from zinc oxide poisoning during zinc–air battery operation, as confirmed by experimental results and density functional theory simulations. In situ X-ray powder diffraction observation confirms that the increased electron cloud density of the surrounding carbon caused by electron delocalization from Selenium Atom could repulse the access of zincate ions, effectively prohibiting the oxide deposition on the air cathode. An amazingly long zinc–air battery cycle life reaching 780 cycles is thus obtained