- Electronic characterization of redox (non)-innocent Fe2S2 reference systems: A multi K-edge X-ray spectroscopic study
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Di-iron dithiolate hydrogenase model complexes are promising systems for electrocatalytic production of dihydrogen and have therefore been spectroscopically and theoretically investigated in this study. The direct effect of ligand substitution on the redox activity of the complex is examined. In order to understand and eventually optimize such systems, we characterised both metal and ligand in detail, using element specific X-ray absorption Fe- and S-K edge XAS. The (electronic) structure of three different [Fe2S2] hydrogenase systems in their non-reduced state was investigated. The effect of one- and two-electron reduction on the (electronic) structure was subsequently investigated. The S K-edge XAS spectra proved to be sensitive to delocalization of the electron density into the aromatic ring. The earlier postulated charge and spin localization in these complexes could now be measured directly using XANES. Moreover, the electron density (from S K-edge XANES) could be directly correlated to the Fe-CO bond length (from Fe K-edge EXAFS), which are in turn both related to the reported catalytic activity of these complexes. The delocalization of the electron density into the conjugated π-system of the aromatic moieties lowers the basicity of the diiron core and since protonation occurs at the diiron (as a rate determining step), lowering the basicity decreases the extent of protonation and consequently the catalytic activity.
- Oudsen,Venderbosch,Korstanje,Tromp
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- Cyclic polysulfides fused to polyaromatics
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Pentathiepins fused to naphthalene and phenanthrene have been synthesized by a simple method. Ring size depends on the stability of generated products related to steric and electronic factors. Sometimes, delocalized π-electron of polyaromatics shows synergistic effect on the stabilization of polysulfur rings. The structures of two polysulfides were also studied by X-ray crystallography and phenanthrene bearing C2S5 ring showed different solid-state properties than corresponding phenanthrene bearing C2S3 ring.
- Alam, Ashraful,Kon-no, Masaru,Ogawa, Satoshi,Sato, Ryu
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- Dehalogenation of Halogenated Nucleobases and Nucleosides by Organoselenium Compounds
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Halogenated nucleosides, such as 5-iodo-2′-deoxyuridine and 5-iodo-2′-deoxycytidine, are incorporated into the DNA of replicating cells to facilitate DNA single-strand breaks and intra- or interstrand crosslinks upon UV irradiation. In this work, it is shown that the naphthyl-based organoselenium compounds can mediate the dehalogenation of halogenated pyrimidine-based nucleosides, such as 5-X-2′-deoxyuridine and 5-X-2′-deoxycytidine (X=Br or I). The rate of deiodination was found to be significantly higher than that of the debromination for both nucleosides. Furthermore, the deiodination of iodo-cytidines was found to be faster than that of iodo-uridines. The initial rates of the deiodinations of 5-iodocytosine and 5-iodouracil indicated that the nature of the sugar moiety influences the kinetics of the deiodination. For both the nucleobases and nucleosides, the deiodination and debromination reactions follow a halogen-bond-mediated and addition/elimination pathway, respectively.
- Mondal, Santanu,Mugesh, Govindasamy
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p. 1773 - 1780
(2019/01/10)
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- The preparation and characterisation of rhodium(III) and Iridium(III) half sandwich complexes with napthalene-1,8-dithiolate, acenaphthene-5,6-dithiolate and biphenyl-2,2′-dithiolate
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The synthesis of rhodium(III) and iridium (III) half sandwich complexes [Cp?M(PEt3) (S-R-S)], M = Rh, Ir; S-R-S = naphthalene-1,8-dithiolate (NaphthS2, a), acenaphthene-5,6-dithiolate (AcenapS2, b) and biphenyl-2,2′-dithiolate (BiphenS2, c) is reported. We also describe the isolation of a new compound acenaphthene-1,8-dithiol. All complexes have been fully characterised using multinuclear NMR spectroscopy and single crystal X-ray diffraction. The ligands naphthalene-1,8-dithiol (H2a), acenaphthene-1,8-dithiol (H2b), 1,1′-biphenyl-2,2′-dithiol (H2c) and benzene-1,2-dithiol (H2d) have also been characterised by single crystal X-ray diffraction.
- Nejman, Phillip S.,Morton-Fernandez, Brian,Black, Nicholas,Cordes, David B.,Slawin, Alexandra M.Z.,Kilian, Petr,Woollins, J. Derek
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- Regioselective deiodination of thyroxine by iodothyronine deiodinase mimics: An unusual mechanistic pathway involving cooperative chalcogen and halogen bonding
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Iodothyronine deiodinases (IDs) are mammalian selenoenzymes that catalyze the conversion of thyroxine (T4) to 3,5,3′-triiodothyronine (T3) and 3,3′,5′-triiodothyronine (rT3) by the outer- and inner-ring deiodination pathways, respectively. These enzymes also catalyze further deiodination of T3 and rT3 to produce a variety of di- and monoiodo derivatives. In this paper, the deiodinase activity of a series of peri-substituted naphthalenes having different amino groups is described. These compounds remove iodine selectively from the inner-ring of T4 and T3 to produce rT3 and 3,3′-diiodothyronine (3,3′-T2), respectively. The naphthyl-based compounds having two selenols in the peri-positions exhibit much higher deiodinase activity than those having two thiols or a thiol-selenol pair. Mechanistic investigations reveal that the formation of a halogen bond between the iodine and chalcogen (S or Se) and the peri-interaction between two chalcogen atoms (chalcogen bond) are important for the deiodination reactions. Although the formation of a halogen bond leads to elongation of the C-I bond, the chalcogen bond facilitates the transfer of more electron density to the C-I σ* orbitals, leading to a complete cleavage of the C-I bond. The higher activity of amino-substituted selenium compounds can be ascribed to the deprotonation of thiol/selenol moiety by the amino group, which not only increases the strength of halogen bond but also facilitates the chalcogen-chalcogen interactions.
- Manna, Debasish,Mugesh, Govindasamy
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body text
p. 4269 - 4279
(2012/04/10)
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- Sulfur monoxide transfer from peri -substituted trisulfide-2-oxides to dienes: Substituent effects, mechanistic studies and application in thiophene synthesis
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Three peri-substituted trisulfide-2-oxides are prepared by treatment of 1,8-naphthalene dithiols with thionyl chloride and pyridine. The 1,2,3-trithiane-2-oxide ring adopts a sofa conformation in the solid state, with a pseudoaxial oxygen and evidence of ring strain (peri-interaction). Heating the trisulfide-2-oxides in the presence of a diene results in formal sulfur monoxide (SO) transfer to form unsaturated cyclic sulfoxides, along with a recyclable 1,8-naphthalene disulfide. The presence of o-methoxy or o-tert-butyl substituents on the naphthalene ring lowers the temperature and increases the rate at which SO transfer occurs. Trapping experiments and kinetic studies are consistent with the generation of triplet SO, followed by in situ trapping by diene. Transfer of SO also occurs upon irradiation at room temperature, but yields of sulfoxide are lower. Dehydration of the sulfoxides under Pummerer conditions gives thiophenes, including the naturally occurring thioperillene. Two dienes form thiophenes directly under the SO transfer conditions. The methodology is applied in a formal synthesis of the antiplatelet medication Plavix.
- Grainger, Richard S.,Patel, Bhaven,Kariuki, Benson M.,Male, Louise,Spencer, Neil
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supporting information; experimental part
p. 5843 - 5852
(2011/06/22)
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- A novel recyclable sulfur monoxide transfer reagent
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(matrix presented) Trisulfide 2-oxide 11 has been prepared from disulfide 9 via reduction to the corresponding dithiol and subsequent trapping with thionyl chloride. Heating trisulfide oxide 11 in the presence of dienes results in transfer of sulfur monoxide to form cyclic unsaturated sulfoxides 13 in good to excellent yields, along with recovery of disulfide 9. A Pummerer reaction can be used to convert the cyclic sulfoxides into thiophenes.
- Grainger, Richard S.,Procopio, Alberto,Steed, Jonathan W.
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p. 3565 - 3568
(2007/10/03)
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- Photochemical studies on the through-space S···S interaction of 2- phenylnaphtho[1,8-de][1,3]dithiin 1-oxide, 5-phenyl[1]benzothieno[4,3,2- def][1,3]benzodithiepin 4-oxide, and 2-phenyldibenzo[d,f][1,3]dithiepin 1- oxide
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2-Phenylnaphtho[1,8-de][1,3]dithiin 1-oxide (4a), 5- phenyl[1]benzothieno[4,3,2-def][1,3]benzodithiepin 4-oxide (4b), and 2- phenyldibenzo[d,f][1,3]dithiepin 1-oxide (4c) underwent facile consecutive photochemical reactions to give the corresponding disulfide, naphtho[1,8- cd][1,2]dithiole (1a), [1]benzothieno[4,3,2-cde][1,2]benzodithiin (1b), and dibenzo[c,e][1,2]dithiin (1c) and benzaldehyde (7), respectively, via the sulfur-sulfur (S···S) interaction. The proposed mechanism for these photochemical reactions is based on the quantum yields measurements, photo- intensity effects, and sensitizer effects. Ab initio calculations were also carried out for a model compound of the primary photoproduct, which showed that the S···S distance becomes shorter and the S-O distance becomes longer upon the excitation to the S1 state.
- Fujii, Takayoshi,Kusanagi, Hiroki,Takahashi, Ohgi,Horn, Ernst,Furukawa, Naomichi
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p. 5027 - 5046
(2007/10/03)
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- Mechanism for photodecomposition of naphtho[1,8-de][1,3] dithiin-1-bis(ethoxycarbonyl)methylides
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Naphtho[1,8-de][1,3]dithiin-1-bis(ethoxycarbonyl)methylides (3) were prepared by the reaction of naphtho[1,8-de]dithiins with diethyl diazomalonate in the presence of copper acetylacetonate. The sulfonium ylides 3 underwent photo-rearrangement giving olefin 5 quantitatively together with naphthalene-1,8-dithiole.
- Fujii, Takayoshi,Sakuragi, Hirochika,Furukawa, Naomichi
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p. 8039 - 8042
(2007/10/02)
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- Aromatic annulation with naphtho[1,8-de]-1,3-dithiin carbocations
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The title carbocations have been produced by the reaction of silver trifluoromethanesulfonate with mixed orthothioesters. Intramolecular aromatic electrophilic substitution (annulation) of the cationic intermediates proceeds readily and provides an efficient, chemoselective route for appending six-membered rings to nonactivated aromatic systems.
- Gamage, Swarna A.,Smith, Robin A. J.
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p. 2111 - 2128
(2007/10/02)
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- Syntheses and Properties of 2,2'-Binaphtho-1,3-dithiinylidene and Its Selenium Analog, 2-(1,3-Dithiol-2-ylidene)naphtho-1,3-dithiin, and 2-(4H-Thiopyran-4-ylidene)naphtho-1,3-dithiin
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In order to discover new electron donors for conducting charge-transfer complexes, the four title compounds 1-4 composed of two heterocycles have been prepared via 1,8-dichalcogen-bridged naphthalene.The cyclic voltammetery indicates that symmetrical 1 and 2 are poor donors, but unsymmetrical 3 and 4 possess considerable donor abilities.The latter compounds are thus capable of forming some crystalline charge-transfer complexes with strong acceptors such as TCNQ, TCNQF4, and DDQ, which are, however, semi-conducting.
- Yui, Koji,Aso, Yoshio,Otsubo, Tetsuo,Ogura, Fumio
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p. 953 - 960
(2007/10/02)
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- SYNTHESES AND PROPERTIES OF BINAPHTHO-1,3-DITHIIN-2-YLIDENE AND ITS SELENIUM ANALOGUE
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With view to discovering new electron donors for low-dimensionally metallic materials, the title compounds were prepared via the corresponding 1,8-dichalcogen-bridged naphthalenes.Their donor characters were examined by cyclic voltammetry, as compared with those of the reference compounds.
- Yui, Koji,Aso, Yoshio,Otsubo, Tetsuo,Ogura, Fumio
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p. 551 - 554
(2007/10/02)
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