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  • 1
    Electronic Resource
    Electronic Resource
    Scavenging effect of melatonin on hydroxyl radicals generated by alloxan (2000)
    Copenhagen : Munksgaard International Publishers
    Journal of pineal research 29 (2000), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Alloxan can act as a generator of reactive oxygen species (ROS) as long as sufficient suitable reducing agents (e.g. reduced glutathione) and oxygen are available. Using electron spin resonance-spectroscopy and the oxygen-centered spin trap DEPMPO, we demonstrate that hydroxyl radicals (OHzrad;) are formed in vitro by alloxan in the presence of glutathione (GSH) and chelated divalent iron. Furthermore, peroxidation of polyunsaturated fatty acids from phosphatidylcholine-containing liposomes with concomitant formation of malondialdehyde (MDA) was used as a further indicator for a preceding OHzrad; formation. Melatonin, the main secretory product of the pineal gland, is an effective scavenger of OHzrad;. The 50%-inhibitor concentration (IC50-value) for melatonin to scavenge OHzrad; generated from the alloxan/GSH-reaction in the presence of ferrous ions was 23 μmol/L. In contrast to the ability to effectively scavenge OHzrad;, the potential of melatonin to prevent lipid peroxidation is considerably less pronounced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-0633.2002.290402.x
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  • 2
    Electronic Resource
    Electronic Resource
    Transformation of barbituric acid into alloxan by hydroxyl radicals: interaction with melatonin and with other hydroxyl radical scavengers (2002)
    Oxford, UK : Munksgaard International Publishers
    Journal of pineal research 33 (2002), S. 0 
    Details
    ISSN: 1600-079X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Barbituric acid (2,4,6-pyrimidinetrione) can be transformed by a non-enzymatic hydroxylation into alloxan (2,4,5,6-pyrimidinetetrone). This transformation can be used as a reaction indicating the formation of hydroxyl radicals (·OH). This conversion was detected using HPLC. Formation of ·OH was demonstrated by electron spin resonance (ESR) spectroscopy combined with spin-trapping techniques. It was shown that ·OH generated via the Fenton reaction abstracts first a hydrogen atom from barbituric acid (BA) and forms intermediately a paramagnetic derivative of BA. After a second attack by another ·OH, the BA radical is transformed into dialuric acid (DA), which autoxidizes via the alloxan radical (·ALX) to ALX. Superoxide radicals (·O2−) are formed during autoxidation of DA and ·ALX. They are able to regenerate ferrous ions. As a result, traces of iron salts are capable of catalyzing the conversion of large amounts of BA into ALX. Several scavengers of ·OH were tested with regard to their efficiency in preventing the transformation of BA into ALX. Of all the scavengers analyzed, melatonin was shown to be one of the most potent compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1034/j.1600-079X.2002.02936.x
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  • 3
    Electronic Resource
    Electronic Resource
    Mössbauer investigations of γ-Fe2O3 particles (1990)
    Springer
    Hyperfine interactions 54 (1990), S. 609-612 
    Details
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Microcrystals of γ-Fe2O3 powder in the size range of single domain particles showing broadened six-line patterns at room temperature in zero applied field were found to behave purely superferromagnetic without any superparamagnetic portion. The broadened patterns have been interpreted on the basis of independent-uniaxial particles with unequal magnetization direction probability which undergo relaxation. Addition of alkaline, dotation with Zn2+ ions and coating by SiO2 cause further line broadening due to relaxation phenomena. The application of a magnetic field did not narrow the line width. This is taken as evidence for incomplete orientation of the magnetization vectors along the direction of the magnetic field. The microcrystals are assumed to subdivide in subdomains which probably possess a size distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02396098
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  • 4
    Electronic Resource
    Electronic Resource
    EPR-Untersuchungen kernchlorierter 4-DimethylaminophenylkationenTeilergebnisse wurden auf der Fotografia Academica, Pardubice, ČSSR, 1982 als Vortrag vorgestellt. (1985)
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 327 (1985), S. 117-120 
    Details
    ISSN: 0021-8383
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: EPR Investigations of Ring Chlorinated 4-DimethylaminophenylcationsThe influence of the position and the number of chlorine atoms in the ring of 4-dimethylaminophenylcations on the zero-field-splitting(zfs) parameter Dis investigated. It was found that the π-donor ability of the chlorine atom(s) ind 2(6)-position(s) increases the zfs parameter D. In the case of 3(5)-substitution the value of D decreases because of the steric hindrance of the dimethylamino-group.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/prac.19853270117
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  • 5
    Electronic Resource
    Electronic Resource
    Untersuchungen an Metallkatalysatoren. XI. Untersuchungen an eisen-, kobalt- und nickelmodifizierten Pt-η-Al2O3-Katalysatoren (1977)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 431 (1977), S. 191-200 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigations on Metal Catalysts. XI. Investigations on Pt—η-Al2O3 Catalysts Modifieded by Iron, Cobalt, and NickelPt—Me—η-Al2O3 catalysts (M: Fe, Co, Ni) were characterized by magnetic investigations, reflectance spectra and determination of dispersity (chemisorption of CO, oxygen-hydrogen titration), respectively.The phase structure of platinum-rich catalysts is composed of a high degree by Pt3Fe super-structure. All the Pt—Fe—η-Al2O3 catalysts contained FeIII ions in octahedral symmetry.The dispersity of the metallic components is determined essentially by their phase structure.
    Notes: Pt—M—η-Al2O3-Katalysatoren wurden mittels magnetischer Resonanz-untersuchungen, Auswertung von Reflexionsspektren und Bestimmung der Metalldispersität (CO-Chemisorption, Sauerstoff-Wasserstoff-Titration) charakterisiert.Der Phasenaufbau platinreicher Katalysatoren ist in starkem Maße durch die Existenz der Pt3Fe-Fernordnungsphase gekennzeichnet. Sämtliche Pt—Fe—η-Al2O3-Katalysatoren enthalten im η-Al2O3 oktaedrisch koordinierte Eisen(III)-Ionen. Es zeigte sich, daß auch die im Trägermaterial ursprünglich vorhandenen Eisen(III)-Ionen mittels Wasserstoff reduziert werden und mit Platin wechselwirken.Die Dispersität der Metallkomponenten wird vorrangig durch deren Phasenstruktur bestimmt.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19774310120
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  • 6
    Electronic Resource
    Electronic Resource
    Untersuchungen an oxidischen Katalystoren. XXVII. UV-VIS-spektroskopische Untersuchungen an CuNaY-Zeolithen (1978)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 445 (1978), S. 65-72 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Studies on Oxide Catalysts. XXVII. Investigations on Zeolites CuNaY with Diffuse Reflectance SpectroscopyThe electronic spectra of CuNaY zeolite samples with different exchange degrees were interpreted in terms of crystal field theory. According to this model the Cu2+ cations are localized independent on exchange degree in three different coordination polyhedrons with symmetries of D4h, C4v, and C3v.With increasing temperature of dehydration (≥473 K) in the electronic spectra of the sample with 8 Cu2+/u. c. occur changes which are caused by formation of oxidic clusters.
    Notes: Die UV-VIS-Spektren von CuNaY-Zeolithen unterschiedlichen Austauschgrades werden im Rahmen der Kristallfeldtheorie interpretiert. Gemäß diesem Modell befinden sich die Kupferionen unabhängig vom Austauschgrad in drei verschiedenen Koordinationspolyedern mit D4h-, C4v- und C3v-Symmetrie.Mit steigender Dehydratisierungstemperatur (≥473 K) treten im Remissionsspektrum der Probe mit 8 Cu2+/EZ charakteristische Änderungen auf, die durch die Ausbildung von oxidischen Clustern hervorgerufen werden.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19784450109
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  • 7
    Electronic Resource
    Electronic Resource
    Untersuchungen an Metallkatalysatoren. X. Zur Charakterisierung von Pt—M-Katalysatoren (M: Fe, Co, Ni) (1977)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 431 (1977), S. 181-190 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigations on Metal Catalysts. X. Characterization of Pt—M Catalysts (M: Fe, Co, Ni)Characterization of carrier-free Pt—M bimetallic catalysts with regard to their phase structure and dispersity were performed with X-Ray powder methods, magnetic investigations, and measurements of dispersity (adsorption of N2, chemisorption of CO, oxygen-hydrogentitration), respectively.The phase structure of the powders is characterized by considerable deviation from the informations on macro crystallites in thermodynamic equilibrium. A. close correlation is given between phase structure and dispersity of the metallic components.
    Notes: Die Charakterisierung trägerfreier Pt—M-Bimetallkatalysatoren (M: Fe, Co, Ni) erfolgte mittels Röntgenphasenanalyse, magnetischer Resonanzuntersuchungen sowie Dispersitätsmessungen (N2-Physisorption, CO-Chemiscorption, Sauerstoff—Wasserstoff-Titration).Die Phasengestaltung der Legierungspulver zeigt teilweise erhebliche Abweichungen von den Angaben für Makrokristalle im thermodynamischen Gleichgewicht. Es besteht ein enger Zusammenhang zwischen Phasengestaltung und Metalldispersität.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19774310119
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  • 8
    Electronic Resource
    Electronic Resource
    Untersuchungen an oxidischen Katalysatoren. XXIX. Spektroskopische und katalytische Untersuchungen an Ni2+-, Co2+-, Cr3+- und Cu2+-ausgetauschten MordenitenProfessor Günther Rienäcker gewidmet (1979)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 452 (1979), S. 6-16 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Studies on Oxide Catalysts. XXIX. Spectroscopic and Catalytic Investigations on Ni2+-, Co2+-, Cr3+-, and Cu2+-exchanged MordenitesNiNaM, CoNaM, CrNaM und CuNaM (M = Mordenite) have been characterized by UV-VIS, EPR and i.r. spectroscopy and the results were compared with the catalytic activity and the activity-time-dependence in the cracking of n-octane and with the shape selectivity in the cracking of a n-octane and isooctane mixture. Water molecules acting as ligands of the exchanged cations are able to dissociate yielding Brönsted acidity. Brönsted sites may be regarded as catalytic active centers in the cracking reaction. Unreduced transition metal cations facilitate the “coking” of the mordenite.The unreduced chromium and cobalt cations for which a position within the main channel is expected, affect the diffusion of the branched paraffin molecule thus increasing shape selectivity.
    Notes: NiNaM, CoNaM, CrNaM und CuNaM (M = Mordenit) wurden durch UV-VIS-Spektroskopie, EPR- und IR-Untersuchungen charakterisiert und die erhaltenen Ergebnisse mit der katalytischen Aktivität und dem Aktivitäts-Zeit-Verhalten dieser Proben bei der Spaltung von n-Octan und der Formselektivität in der Spaltung eines Gemisches von n/iso-Octan verglichen. Wassermolekeln als Liganden der eingetauschten Kationen können dissoziieren und so einen Beitrag zur Brönsted-Acidität liefern. Die Brönsted-Zentren können als katalytisch aktive Zentren in der Spaltreaktion angesehen werden. Nichtreduzierte Übergangsmetallkationen vergrößern die Neigung des Mordenits zum „Verkoken“ wesentlich. Die nichtreduzierten Co2+- und Cr3+-Kationen, für die eine Position im Hauptkanal angenommen werden kann, wirken als zusätzliche Diffusionsbremse auf die verzweigte Paraffinmolekel und erhöhen die Formselektivität des Mordenits.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19794520103
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  • 9
    Electronic Resource
    Electronic Resource
    Untersuchungen an Nickeloxid-Mischkatalysatoren. I. Strukturelle Eigenschaften von NiO/SiO2-KatalysatorenProfessor Heinrich Bremer zum 60. Geburtstage am 22. August 1980 gewidmet (1980)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 467 (1980), S. 43-50 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Studies on Nickel Oxide Mixed Catalysts. I. Structural Properties of NiO/SiO2 CatalystsStructural properties of NiO/SiO2 catalysts prepared by precipitation-deposition and impregnation have been investigated. A nickel-layer-silicate like structure is formed only in the precipitated catalysts showed infrared spectroscopic measurements. After thermal treatment at 723 K by means of magnetic measurements and reflectance spectroscopy besides Ni2+ ions in octahedral environment tetrahedral coordinated Ni2+ions were found. The part of tetrahedral coordinated Ni2+ ions is independent of the NiO-content up to 40 mole % NiO. Nickel oxide is formed above a content of 40 mole %.In the case of the impregnated catalysts nickel oxide cluster are formed on the surface after annealing at 723 K.
    Notes: Es wurden die strukturellen Eigenschaften von durch Fällung und Tränkung hergestellten NiO/SiO2-Katalysatoren untersucht. Infraspektroskopische Messungen zeigten, daß sich bei den durch Fällung hergestellten Katalysatoren wenig strukturierte Nickelschichtsilikate bilden. Nach thermischer Behandlung bei 723 K wurden durch magnetische und UV-VIS-reflexionsspektroskopische Untersuchungen neben Ni2+-Ionen in oktaedrischer Sauertoffkoordination auch tetraedrisch koordinierte Ni2+-Ionen nachgewiesen. Der Anteil an tetraedrisch koordinierten Ni2+-Ionen ist bis 40 Mol-% NiO nicht vom NiO-Gehalt abhängig.Im Unterschied dazu sind bei den durch Tränkung hergestellten Katalysatoren die Wechsel-wirkungen zwischen den Komponenten gering. Auf der Oberfläche dieser Katalysatoren bilden sich nach Temperung Nickeloxidcluster.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19804670106
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  • 10
    Electronic Resource
    Electronic Resource
    Untersuchungen an Metallkatalysatoren. XXVII. Zum Einfluß verschiedener Träger auf die Dispersität von Nickel (1981)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 472 (1981), S. 162-172 
    Details
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Investigations on Metal Catalysts. XXVII. On the Influence of Several Carriers on the Dispersion of NickelNickel supported catalysts (carrier: η-, ϑ-, α-Al2O3, TiO2) were characterized by chemically determined degree of reduction, CO chemisorption, magnetic susceptibility measurements and FMR. The influence of interaction between carrier and active component in the unreduced state on the size and number of Ni crystallites is discussed.
    Notes: Nickel/Trägerkatalysatoren auf Basis von η-, ϑ-, α-Al2O3 bzw. TiO2 wurden durch den chemisch bestimmten Reduktionsgrad der Aktivkomponente, mittels CO-Chemisorption sowie durch statische Suszeptibilitätsmessungen und ferromagnetische Resonanz charakterisiert. Es wird der Einfluß der Wechselwirkung zwischen Träger und Aktivkomponente im unreduzierten Zustand auf die Nickel-Kristallitgröße und deren Anzahl diskutiert.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/zaac.19814720119
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