Internal Redox Research Articles

Thermal decomposition of a hydrated pyrochlore containing mixed-valence bismuth(III, V) and potassium

The study of the pyrolysis of the pyrochlore [K 1.13Bi 0.34 3+] [Bi 0.22 3+Bi 1.78 5+] O 5.86(H 2O) 0.97 by DTA, TGA, gas chromatography and high temperature X-ray diffraction shows a three-step decomposition: an internal redox reaction involving Bi 5+ and OH − ions, a dehydration and finally an internal redox reaction involving Bi 5+ and O 2− ions. The structure remains of the pyrochlore type up to 310°C, despite the creation of a large amount of vacancies in the octahedral framework.

The cyanide-catalyzed conversion of β-formylmuconates into triglochinates: A useful biomimetic synthesis

Upon treatment with cyanide under slightly basic conditions, β-formyl- cis,cis-muconic acid and esters, prepared from vanillin, undergo a sequence of prototropic shifts equivalent to an internal redox process in which 1,4-reduction of the diene system is blanaced by oxidation of the formyl group.

Household and Lineage in Renaissance Florence: The Family Life of the Capponi, Ginori, and Rucellai. Francis William Kent

Previous articleNext article No AccessReviewsHousehold and Lineage in Renaissance Florence: The Family Life of the Capponi, Ginori, and Rucellai. Francis William Kent Richard A. GoldthwaiteRichard A. Goldthwaite Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Speculum Volume 53, Number 4Oct., 1978 The journal of the Medieval Academy of America Article DOIhttps://doi.org/10.2307/2849806 Views: 2Total views on this site Citations: 1Citations are reported from Crossref Copyright 1978 The Mediaeval Academy of AmericaPDF download Crossref reports the following articles citing this article:H. J. Gysling, M. Lelental, M. G. Mason, L. J. Gerenser Non-Silver Amplification Processes: Part 3. Catalytic Thermal Decomposition of Te( II ) Coordination Complexes via Internal Redox Reactions, The Journal of Photographic Science 30, no.22 (Jul 2016): 55–65.https://doi.org/10.1080/00223638.1982.11738156

Assay conditions and the demonstration of nitroimidazole resistance in Tritrichomonas foetus.

Tritrichomonas foetus KV(1), a nitroimidazole-susceptible strain, and KV(1)/M100, its nitroimidazole-resistant daughter strain, differed markedly in their in vivo susceptibility to metronidazole. In vitro susceptibility testing in multiwell plates and tubes with different trichomonad media containing no, or low concentrations of, ascorbate demonstrated that the resistant strain behaves like the susceptible one, if tested under anaerobic conditions (deep cultures in tubes or multiwell plates in anaerobic jars), but shows resistance if tested in the presence of air (multiwell plates exposed to air). In media containing high concentrations of ascorbate, no resistance was observed even in air. The results suggest that the two strains differ in the regulation of internal redox systems and underscore the role testing methods may play in the in vitro detection of nitroimidazole-resistant protozoan parasites.

Kinetics and mechanism of substitution reactions of (dimethylsulfoxide)pentaamminecobalt(III) ion in dimethylsulfoxide solvent: complications due to redox and conjugate base processes

Simple anation and solvent exchange reactions of Co(NH3)5DMSO3+ in DMSO are accompanied by reactions in which the conjugate base of this complex undergoes either internal redox to cobalt(II) or relatively rapid substitution. These conjugate base reactions are eliminated by addition of H+, although a minor redox pathway persists within ion pairs of Co(NH3)5DMSO3+ with chloride or bromide. The latter pathway is evidently not mechanistically related to the solvent exchange or anation reactions, which proceed by dissociative interchange (Id) according to the activation parameters (volume of activation = +10 cm3 mol−1 for DMSO exchange; enthalpy of activation = 123, 121, and ∼126 kJ mol−1 for DMSO exchange and bromide and chloride anation respectively). Enthalpies of activation for solvent exchange and for the limiting anation rate are shown to be better criteria of mechanism than the corresponding rate coefficients.

ChemInform Abstract: REDOX DECOMPOSITION OF TRANS‐TETRA‐AMMINEAQUOSULPHITOCOBALT(III) IN AQUEOUS SOLUTION

AbstractKinetik und Mechanismus der zu Co" führenden Zersetzung des Komplexes (I) in wäßriger saurer Lösung werden untersucht.

Redox decomposition of trans-tetra-ammineaquosulphitocobalt(III) in aqueous solution

The complex trans-[Co(NH3)4(H2O)(SO3)]+ decomposes to Co2+ in aqueous acid solution. Kinetic plots exhibit an initial period of curvature followed by a first-order process, kobs=(1·14 ± 0·03)× 10–4 s–1 at 25·0 °C, ΔH‡= 26·5 ± 0·1 kcal mol–1, and ΔS‡= 12·5 ± 0·4 cal K–1 mol–1[I= 1·00M(LiClO4)]. The rate of reaction is independent of [H+] in the range 0·01–1·00M. A mechanism is proposed relating kobs to a rate-determining isomerisation to the cis-complex, followed by rapid conversion to the complex [Co(NH3)3(H2O)2(SO3)]+ which probably undergoes an internal redox reaction. Somewhat higher rates have been observed in the presence of molecular oxygen and evidence is presented for formation of the free radical HSO3.

Reduction by sulphoxides : The mechanism of deoxygenation of heterocyclic N-oxides and tertiary amine N-oxide

Heterocyclic and tertiary amine N-oxides undergo an acid-catalysed deoxygenation by sulphoxides at elevated temperatures. The reductions are rationalized by postulating the formation of an initial coordination complex formed by attack of the nucleophilic N-oxide oxygen atom on the sulphur atom of the sulphoxide or its conjugate base. This complex may undergo an internal redox reaction to give a sulphone and amine or alternatively be attacked by a nucleophilic species (presumably sulphoxide oxygen) to produce a sulphinate and amine. Both decomposition pathways were observed. Deoxygenation of heterocyclic N-oxides, however, proceeds primarily by the second route and that of aliphatic amine oxides by the first decomposition process. These observations are rationalized mechanistically. The effect of varying the N-oxide substrates and the sulphoxides has also been examined.

Complexation of tellurium(II) with thioglycolic acid and reactivity patterns of the system

Interaction of Te(IV) with excess thioglycolic acid (TGA) in strongly acid media leads to formation of yellow diamagnetic soluble S-ligated thioglycollato-tellurium(II) neutral and anionic complexes. The neutral bis-complex is highly unstable with respect to autodecomposition to Te(O) and dithiodiglycolic acid but the anionic higher complexes are stable in absence of competing ligands. The solid H 2[Te II(TGA-H) 4] was isolated and characterised. Unlike with Te(II)-thiourea complexes, presence of halides did not stabilise but actually destabilised the Te(II)-TGA system, the effect being I ⪢ Br ⪢ Cl. Addition of thiourea also caused decomposition of the Te(II)-TGA system. The results have been rationalised on the basis of the instability of the Te(II)-(TGA-H) 2 species with respect to an internal redox reaction. Addition of Hg(II) to Te(II)-TGA systems caused oxidation of Te(II) to Te(IV) in absence of halide ions and interestingly to the formation of the Hg(II) chalcohalides of composition, Hg 3Te 2 X 2 ( X = Cl,Br,I) in presence of halides.

Model Studies on Flavin-Dependent Carbonyl-Activation: Reduction of Carbonyl Compounds by Flavohydroquinone

The reduction of aldehydes by flavohydroquinone to yield the corresponding alcohols and flavoquinone is reported and discussed in view of its relevance to the mechanism of flavin-dependent dehydrogenation and carbonyl activation. With formaldehyde and flavohydroquinone formation of a covalent 5- (HO - CH2) Flred⁻ intermediate species is observed. In a reverse reaction 5-methylflavoquinonium cation undergoes an internal redox reaction to yield flavohydroquinone and formaldehyde.

Reactivity of vinyl sulphonic esters. Part XI. Behaviour of aminovinyl p-bromobenzenesulphonates

1,2-Diaryl-2-[(N-aryl) methylamino] vinyl p-bromobenzenesulphonates, prepared by reactions of α-aryl-α-[(N-aryl) methylamino] acetophenone derivatives with p-bromobenzenesulphonyl chloride and sodium hydride, undergo two kinds of reactions. One formally involves intermediate formation of β-aminovinyl cations to give substitution products and/or cyclisation to give indole derivatives along with p-bromobenzenesulphonic acid. The other is a novel internal redox reaction which affords benzil derivatives together with p-bromobenzenesulphinic acid, and is catalysed, in inert solvents, by boron trifluoride. The cyclisation to indoles, which is catalysed by aluminium trichloride, occurs without rearrangement, indicating that a β-nitrogen atom in contrast to a β-sulphur atom, does not participate in the reaction by bridging between the two ethylenic carbon atoms.

Light-induced reduction of pyridine nucleotide and its relation to light-induced electron transport in whole cells of Rhodospirillum rubrum

Fluorometric measurements of the light induced reduction of pyridine nucleotide (presumably NAD +) were carried out in living cells of Rhodospirillum rubrum. The rate vs. light intensity curves were different in cells from older cultures as compared with cells from young cultures. In young cells pyridine nucleotide was reduced only by higher intensities of the actinic light. The cytochrome oxidized at these intensities was cytochrome c 2 and the light-induced absorbance changes in the near-infrared spectral region showed only the photooxidation of P870. The uncoupler of photophosphorylation carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) inhibited the pyridine nucleotide photoreduction which could be restored partially by cysteine but not by O 2. In older cells pyridine nucleotide was reduced also at low intensities of the actinic light. If such cells were kept in the dark for a couple of days in a substrate-free medium, pyridine nucleotide was reduced efficiently in the light and the cytochrome predominantly oxidized, even at higher intensities, was C428. The light- minus-dark spectrum in the near-infrared spectral region showed few signs of the photooxidation of P870. Instead, a red shift of an absorption band at 880 nm was observed. FCCP inhibited the pyridine nucleotide photoreduction also under these conditions but the photoreduction could be restored by O 2. The results were interpreted as indicating that this organism uses an energy-linked reversal of electron flow mediated by a high-energy intermediate produced during a light-induced cyclic electron transport when in an early stage of their development. Older cells can use an alternative mechanism for the reduction of pyridine nucleotide. This mechanism probably is a direct light-induced electron transport from exogenous as well as from endogenous substrates to the pyridine nucleotide. The switching over from one mechanism to another is related to the internal redox potential. The present results support a different type of reaction center for each mechanism, although an interpretation based on one reaction center operating both electron transport systems cannot be ruled out.

A new reductimetric reagent: iron II in a strong phosphoric acid medium—II : Titration of molybdenum VI with iron II at room temperature

The results are presented of investigations leading to the development of a procedure for the titrimetric determination of molybdenum VI with iron II sulphate in a strong phosphoric acid medium (11.5–13.0 M) at room temperature, using either a potentiometric end-point or a visual end-point with methylene blue or thionine as an internal redox indicator. Advantages of the procedure are similar to those previously described for the titration of uranium VI with iron II.

A new reductimetric reagent: iron II in a strong phosphoric acid medium : Titration of uranium VI with iron II at room temperature

The formal redox potential of the Fe III/Fe II couple has been determined in media of varying phosphoric acid concentration, and found to decrease steeply with increasing phosphoric acid concentration. Above a certain concentration of phosphoric acid, the difference between the formal potentials of the U VI/U IV and Fe III/Fe II couples becomes sufficiently great to enable iron II to reduce uranium VI even at room temperature. This is the reversal of the normal redox reaction—oxidation of uranium IV by iron III. A careful study of the various factors involved has enabled us to develop a new reductimetric titration of uranium VI with iron II in strong phosphoric acid medium (11.0 to 13.5 M) at room temperature using either a potentiometric end-point or a visual end-point with methylene blue or thionine as an internal redox indicator. Because the new procedure enables the titration to be carried out at room temperature, it is more convenient than procedures involving titanium III and chromium II which require temperatures ranging from 60 to 90°. The new procedure has a further advantage in that it can be used for the determination of uranium VI even in the presence of iron III and tungsten IV, using an electrometric end-point. Also, the new procedure does not require the elaborate precautions which are necessary for the preparation and storage of titanium III or chromium II solutions.

The chemistry of osmium. Part VI. The use of tris o,phenanthroline osmium II perchlorate as an internal redox indicator

The chemistry of osmium. Part VI. The use of tris o,phenanthroline osmium II perchlorate as an internal redox indicator