Search results for "Redox"
showing 10 items of 619 documents
The first spiroconjugated TTF- and TCNQ-type molecules: a new class of electroactive systems?
2005
[Structure: see text] Spiroconjugated TTF-type electron donors (13a-c) and TCNQ-type electron acceptors (10, 11) have been prepared from spiroquinone 9. Cyclic voltammetry reveals a relatively weak accepting ability for 10 and 11, and a strong electron-donor character for 13a-c. Whereas the spiroconjugation introduces a destabilization of the LUMO for compounds 9-11, the opposite is observed for compound 13, thus justifying the redox potential values.
Kinetic and functional characterization of a membrane-bound NAD(P)H dehydrogenase located in the chloroplasts of Pleurochloris meiringensis (Xanthoph…
1996
Using isolated chloroplasts or purified thylakoids from photoautotrophically grown cells of the chromophytic alga Pleurochloris meiringensis (Xanthophyceae) we were able to demonstrate a membrane bound NAD(P)H dehydrogenase activity. NAD(P)H oxidation was detectable with menadione, coenzyme Q0, decylplastoquinone and decylubiquinone as acceptors in an in vitro assay. K m-values for both pyridine nucleotides were in the μmolar range (K m[NADH]=9.8 μM, K m[NADPH]=3.2 μM calculated according to Lineweaver-Burk). NADH oxidation was optimal at pH 9 while pH dependence of NADPH oxidation showed a main peak at 9.8 and a smaller optimum at pH 7.5-8. NADH oxidation could be completely inhibited with…
Redox-induced coordination isomerization of a phosphoniobenzophospholide.
2003
1-Triphenylphosphoniobenzo[c]phospholide 1 reacts with [M(CO)(5)Br] (M = Mn, Re) and [Mn(CO)(3)(naphthalene)][BF(4)] to give complexes cis-[M(CO)(4)(1)Br] (5 a,b) and [Mn(CO)(3)(1)][BF(4)] (6 a[BF(4)]), respectively, featuring eta(1)(P)- and eta(5)(pi)-coordination of the phosphole ring. The corresponding reactions with [M(2)(CO)(10)] proceed with conservation of the metal-metal bond and yield, depending on the reaction temperature, dinuclear complexes [M(2)(CO)(8)(1)] (M=Mn, 7 a) or [M(2)(CO)(6)(1)(2)] (M=Mn, Re, 8 a,b) with mu(2)-bridging eta(1)(P):eta(2)(Pdbond;C) coordination of the phosphole moiety. All complexes formed were characterized by spectroscopic data; 5 b, 6 a[BF(4)], and 8 a…
Ferrocenyl-Labeled Sugar Amino Acids: Conformation and Properties
2012
Novel organometallic sugar amino acid conjugates 1–5 have been prepared by amide coupling of O-protected N-acetylmuramic acid and iso-muramic acid (2-[3-amino-2, 5-dihydroxy-6-(hydroxymethyl)oxan-4-yl]oxypropanoic acid) with 1-aminoferrocene, 1-aminoferrocene-1′-carboxylic acid (H-Fca-OH), or 1, 1′-diaminoferrocene, respectively. The influence of the ferrocenyl moiety and presence of additional remote potential hydrogen atom acceptors and donors at the ferrocenyl core on the conformation and lipophilicity is investigated by TLC, IR, NMR, and CD spectroscopic methods augmented by density functional calculations. Furthermore, the redox potential of the ferrocene/ferrocenium couple is tuned by…
Impact of O → S Exchange in Ferrocenyl Amides on the Structure and Redox Chemistry
2014
The conformations and redox chemistry of ferrocenyl amides have been investigated in considerable depth in the last few years, while ferrocenyl thioamides have attracted less interest so far, although distinctly different conformations and reactivity patterns are expected. Monoferrocenyl amides Fc-NHC(O)CH3 (1) and 1,1′-CH3O(O)C-Fn-NHC(O)CH3 (2) and diferrocenyl amides Fc-NHC(O)-Fc (5) and Fc-NHC(O)-Fn-NHC(O)CH3 (6) are easily transformed into the corresponding thioamides (3, 4, 7, 8) by treatment with Lawesson’s reagent (2,4-bis(p-methoxyphenyl)-1,3-dithiaphosphetane-2,4-disulfide) (Fc = Fe(C5H4)(C5H5), Fn = Fe(C5H4)2). The thioamide conformations (cis/trans) in 3, 4, 7, and 8 and the hydr…
Electrocatalytic Properties of Carbosilane‐Based Hyperbranched Polymers Functionalized with Interacting Ferrocenyl Units
2012
Two types of hyperbranched ferrocene-containing polycarbosilanes were obtained by hydrosilylation of polydiallylmethylsilane (hb-PDAMS) and polymethyldiundecenylsilane (hb-PMDUS) with diferrocenylmethylsilane. The redox properties of both polymers have been investigated both in solution and confined onto platinum electrodes. The electrocatalytic activity of polymer-modified electrodes toward the reduction of oxygen as well as the electrochemical reduction and oxidation of hydrogen peroxide has been examined.
Mononuclear mixed oxosulfidomolybdate(VI) complexes with aminodicarboxylic ligands. Synthesis and spectroscopic characterization by multinulcear magn…
1993
Addition of B2S3 to a methanolic solution of the MoVIO3L2− complex (L=N,N-bis(ethanoic acid)-1-amino-2- methylthio-ethane) results in the formation of two different monomeric oxosulfidomolybdate(VI) complexes, [MoO2SL]2− and [MoOS2L]2− as indicated by 1H, 13C, 17O and 95Mo NMR spectroscopy and by the reaction of these two sulfurated species with triphenylphosphine. The temperature dependences of the 1H NMR spectra indicate exchange processes for both sulfido complexes. Their redox properties are discussed and contrasted with those observed for the parent fac-trioxo molybdenum(VI) complex. The primary synthetic route to mixed oxosulfido [MoO3−nSnL]2− complexes described here can be extended …
Are Heme-Dependent Enzymes Always Using a Redox Mechanism? A Theoretical Study of the Kemp Elimination Catalyzed by a Promiscuous Aldoxime Dehydratase
2020
The design of biocatalysts is a goal to improve the rate, selectivity and environmental friendship of chemical processes in biotechnology. In this regard, the use of computational techniques has provided valuable assistance in the design of enzymes with remarkable catalytic activity. In this paper, hybrid QM/MM simulations have allowed getting an insight into the mechanism of a promiscuous aldoxime dehydratase (OxdA) for the Kemp elimination. We first demonstrate that, based on the use of linear response approximation (LRA) methods, the lowest energy electronic state of the benzisoxazole placed in the active sit of OxdA corresponds to a singlet state, being the triplet and the quintet state…
Structural Rearrangements in Triple-Decker-Like Complexes with Mixed Group 15/16 Ligands: Synthesis and Characterization of the Redox Couple [Cp2*Fe2…
2001
The reaction of As4Se4 with stoichiometric amounts of [Cp*Fe2(CO)4] (Cp* = C5Me5) in boiling toluene forms [Cp2*Fe2As2Se2] (1) in good yield. X-ray crystallography shows 1 to have a triple-decker structure which comprises a tetraatomic mu,eta4:4-As2Se2 ligand. Density functional theory (DFT) and extended Huckel molecular orbital (EHMO) calculations confirm that the As2Se2 ligand behaves as a four-electron pi donor. Oxidation of 1 with equimolar amounts of [(C5H5)2Fe]PF6, Br2 and I2, respectively, gave compounds 2-4. According to X-ray crystallographic investigations that were carried out on 2 and 4, the oxidation state has a considerable influence on the structure of the Fe2As2Se2 core: sig…
How Humic Substances Dominate Mercury Geochemistry in Contaminated Floodplain Soils and Sediments
1998
The interaction of mercury (Hg) and humic substances (hs) was studied in floodplain topsoils and surface sediments of the contaminated German river Elbe. An intimate coupling exists between the geochemical cycles of Hg and organic carbon (OC) in this ecosystem. Humic substances exert a dominant influence on several important parallel geochemical pathways of Hg, including binding, transformation, and transport processes. Significant differences exist between the Hg-hs associations in floodplains and sediments. Both humic acids (ha) and fulvic acids (fa) contribute to Hg binding in the sediments. In contrast, ultrafiltration experiments proved that Hg in the floodplain soils is almost exclusi…