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Electron-transfer Mechanism (electron-transfer + mechanism)
Selected AbstractsCopper-containing nitrite reductase from Pseudomonas chlororaphis DSM 50135FEBS JOURNAL, Issue 12 2004Evidence for modulation of the rate of intramolecular electron transfer through nitrite binding to the type 2 copper center The nitrite reductase (Nir) isolated from Pseudomonas chlororaphis DSM 50135 is a blue enzyme, with type 1 and type 2 copper centers, as in all copper-containing Nirs described so far. For the first time, a direct determination of the reduction potentials of both copper centers in a Cu-Nir was performed: type 2 copper (T2Cu), 172 mV and type 1 copper (T1Cu), 298 mV at pH 7.6. Although the obtained values seem to be inconsistent with the established electron-transfer mechanism, EPR data indicate that the binding of nitrite to the T2Cu center increases its potential, favoring the electron-transfer process. Analysis of the EPR spectrum of the turnover form of the enzyme also suggests that the electron-transfer process between T1Cu and T2Cu is the fastest of the three redox processes involved in the catalysis: (a) reduction of T1Cu; (b) oxidation of T1Cu by T2Cu; and (c) reoxidation of T2Cu by NO2,. Electrochemical experiments show that azurin from the same organism can donate electrons to this enzyme. [source] Photodegradation mechanism and stabilization of polyphenylene oxide and rigid-rod polymersPOLYMER INTERNATIONAL, Issue 2 2006Ying-Hung So Abstract Poly(2,4-dimethyl-1,4-phenylene oxide) (PPO), poly(benzo[1,2- d:5,4- d,]bisoxazole-2,6-diyl-1,4-phenylene) (PBO) and poly(benzo[1,2- d:4,5- d,]bisthiazole-2,6-diyl-1,4-phenylene) (PBZT), which are polymers with extended conjugated structures, undergo a self-sensitized photo-induced electron-transfer reaction. A second component is not required. This article presents many similar observations on these polymers when they are exposed to light and evidence to support the proposed photo-induced electron-transfer mechanism. Methods to stabilize these polymers against photo-oxidation are also described. Workers investigating other conjugated polymeric systems may find the experimental methods, observations and polymer stabilization approaches discussed in this review useful. Copyright © 2005 Society of Chemical Industry [source] New Insight into the Mode of Action of Nickel Superoxide Dismutase by Investigating Metallopeptide Substrate ModelsCHEMISTRY - A EUROPEAN JOURNAL, Issue 2 2009Daniel Tietze M. Abstract For the first time, the existence of a substrate adduct of a nickel superoxide dismutase (NiSOD) model, based on the first nine residues from the N terminus of the active form of Streptomyces coelicolor NiSOD, has been proven and the adduct has been isolated. This adduct is based on the cyanide anion (CN,), as a substrate analogue of the superoxide anion (O2.,), and the nickel metallopeptide H-HCDLPCGVY-NH2 -Ni. Spectroscopic studies, including IR, UV/Vis, and liquid- and solid-state NMR spectroscopy, show a single nickel-bound cyanide anion, which is embedded in the metallopeptide structure. This complex sheds new light on the question of whether the mode of action of the NiSOD enzyme is an inner- or outer-sphere mechanism. Whereas discussion was previously biased in favor of an outer-sphere electron-transfer mechanism due to the fact that binding of cyanide or azide moieties to the nickel active site had never been observed, our results are a clear indication in favor of the inner-sphere electron-transfer mechanism for the disproportionation of the O2., ion, whereby the substrate is attached to the Ni atom in the active site of the NiSOD. [source] Radical-scavenging polyphenols: new strategies for their synthesisJOURNAL OF PHARMACY AND PHARMACOLOGY: AN INTERNATI ONAL JOURNAL OF PHARMACEUTICAL SCIENCE, Issue 12 2007Paolo Bovicelli New strategies for the synthesis of polyphenols, compounds with antioxidant properties contained in every kind of plants, are discussed. Syntheses of different classes of polyphenols, namely ubiquinones, present in many natural systems in which electron-transfer mechanisms are involved, hydroxy-tyrosol, one of the main components of the phenol fraction in olives, and flavonoids, widespread in the plant kingdom, were approached by simple and environmentally sustainable methods. [source] | ||||||||||