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  • 1
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature structural biology 5 (1998), S. 1084-1090 
    ISSN: 1072-8368
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Catechol oxidases are ubiquitous plant enzymes containing a dinuclear copper center. In the wound-response mechanism of the plant they catalyze the oxidation of a broad range of ortho-diphenols to the corresponding o-quinones coupled with the reduction of oxygen to water. The crystal structures of ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Fresenius' journal of analytical chemistry 364 (1999), S. 184-188 
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A flow injection analysis (FIA) method for the automated determination of hydrogen peroxide in the presence of even stronger oxidants is presented based on the immediate formation of a colored adduct between hydrogen peroxide and a dinuclear iron(III) complex. A reagent stream with the complex and a carrier stream into which the sample is injected are combined in a low dead volume mixing tee. A reaction coil provides for a reaction time of 7 s, after which detection is performed using UV/ vis spectroscopy at 575 nm. Major advantages of the method are the simple experimental setup and the high selectivity even towards stronger oxidants. Real samples have been investigated and the method has been validated using independent techniques including microplate spectrophotometry and HPLC.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1434-1948
    Keywords: Iron(III) ; Peroxo Complexes ; Kinetics ; Hydrogen Peroxide ; Catalase ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The new diiron complex [Fe2(tbpo){O2As(CH3)2}(CH3O)(CH3OH)](ClO4)3 · 5 CH3OH · 2 H2O (1) containing a (μ-alkoxo)(μ-dimethylarsinato)diiron(III) core was synthesized using the heptadentate ligand N,N,N′,N′-Tetrakis(2-benzimidazolylmethyl)-1,3-diamino-2-propanol (Htbpo). The complex was characterized structurally by X-ray crystallography. 1reproduces the coordination mode and the stoichiometry of the proposed purple acid phosphatase-arsenate inhibitor complex. More importantly, 1 is a good functional model for the activation of small molecules, since the solvent molecule in the coordination sphere of each iron ion can be substituted very easily by a small substrate molecule. This is confirmed by the comparatively high pH-dependent catalase-like activity of 1. In order to study the influence of the cacodylate bridge on the formation of the metastable adduct with hydrogen peroxide, the analogous hydroxo-bridged complex [Fe2(tbpo)(OH)(NO3)2](NO3)2 · CH3OH · 2 H2O (2) was employed. The reactions of 1and 2 with H2O2 were studied as a function of [H2O2], pH, temperature, and pressure, and the kinetic results including the activation parameters are reported. In the case of compound 2 the reaction proceeds in one step, and the observed first order rate constant, kobs, shows a linear dependence on the hydrogen peroxide concentration with a zero intercept. For complex 1 the kinetic traces could be fitted to two exponential functions. One of the observed pseudo-first-order rate constants, kobs1, exhibits a linear dependence on the hydrogen peroxide concentration with a zero intercept, whereas the other rate constant, kobs2, was independent of the hydrogen peroxide concentration. A mechanistic interpretation is presented.Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2005/1999/99068_s.pdf or from the author.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    Journal für Praktische Chemie/Chemiker-Zeitung 337 (1995), S. 113-124 
    ISSN: 0941-1216
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The hydrogen abstraction of radical intermediates yielded by radical addition to the methylene compound 6, shows excellent facial selectivity. Conformational analyses of the radical intermediates were carried out by quantum chemical calculations and explain these results. The chiral radicals 7 and 8, yielded from the chiral bromides 3 and 4, lead with ethyl acrylate to the adducts 28 and 29 with more 96% de. The adduct 28 was converted to the optically active γ-valerolactone 30. The structures of the bromides 3, 4 and 31 as well as the radical adducts 19a, 24 and 25 have been verified by X-ray diffraction analysis.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 0947-6539
    Keywords: heterocycles ; insertion reactions ; phosphaalkynes ; phosphorus ylides ; triphosphetenes ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Hitherto unknown 1,2,3-triphosphetenes RC=P—PCF3—PCF3 (3a-d) are formed as main products in reactions of phosphaalkynes R—C≡P [R = iPr2N (1a), tBu (1b), Me2EtC (1c), 1-methylcyclohexyl (1d)] with the cyclotetraphosphane (PCF3)4 (2). According to NMR results the CF3 groups in 3a-d have a trans disposition; an X-ray diffraction study of 3a confirms this structure. The P—P bond lengths in 3a are equal [2.201 (2) and 2.204 (2) Å] and correspond to single bonds. A considerable shortening is observed for the sp2-C-N bond (1.336 Å) which, together with the elongation of the P=C bond (1.746 Å), indicates effective π donation of the lone pair on nitrogen. Surprisingly, 3a can be prepared in quantitative yields by reaction of the PP ylide Me3P=PCF3 (6) with 1 a (molar ratio: 2:1). In contrast, the corresponding reactions of 6 with the alkyl-substituted phosphaalkynes 1b-d lead to the novel phosphorus ylides Me3P=C(R)—P—PCF3—PCF3PCF3 [R = tBu (10a), Me2EtC (10b), 1-methylcyclohexyl (10c)] in good yields. In their molecular groundstate structures, determined by X-ray diffraction, the lone pair on the phosphano P atom prefers the syn position with respect to the ylidic P=C bond. An unusual lengthening of the sp2-C-C bond [1.553 (4) (10a), 1.543 (6) (10b), 1.551 (4) Å (10c)] to values typical for sp3-C/sp3-C distances is observed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 3 (1997), S. 1232-1237 
    ISSN: 0947-6539
    Keywords: antimony ; heteropolyanions ; polyoxometalates ; synthesis design ; tungsten ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Proceeding from the α-B-SbW9O33 fragment 1, various novel large heteropolyanions ([Na2Sb8W36O132(H2O)4]22- (2), [Sb2W22O74(OH)2]12- (3) and [Sb2W20M2O70(H2O)6](14-2n)- (4); Mn+ = Fe3+, Co2+, Mn2+, Ni2+) have been obtained in crystalline form by systematic synthesis. Their unexpected structures have been studied by X-ray diffraction: 2, 3 and 4 contain β-SbW9 units connected to each other by Sb3+ ions, WO2/WO2OH groups, and WO2/Mn+ (H2O)3 groups, respectively. Structural details and especially the systematic synthesis strategy for the formation of these interesting polytungstates are discussed in order to explain the unusual behaviour of 1 in aqueous solution under different reaction conditions.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 1130-1137 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Crystal Structure of N-NitrosodimethylamineThe crystal structure of the title compound has been determined from single crystal low temperature X-ray counter data collected at - 130°C. Bond lengths in the exactly planar molecule were found to be N — N 1.320(6), N — O 1.260 (6), C — N 1.461 (7) and 1.465 (7) Å. The bonding in the molecule is significantly closer to the polar structure compared to the free molecule in the gas phase, this being stabilised by intermolecular π interactions perpendicular to the planes of the molecules.
    Notes: Die Struktur des festen N-Nitrosodimethylamins bei - 130°C wurde durch Röntgenstruktur-analyse bestimmt. Das Molekül ist im Kristall exakt planar. Die Bindungslängen bei - 130°C sind: N — N 1.320(6), N — O 1.260(6), C — N 1.461(7) und 1.465(7) Å. Senkrecht zu den Molekülebenen verlaufende intermolekulare π-Wechselwirkungen stabilisieren einen höheren Anteil der polaren Struktur am Bindungszustand gegenüber dem freien Molekül der Gasphase.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 109 (1976), S. 2622-2627 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Crystal and Molecular Structure of 4,4,6,6-Tetrafluoro-1,3,5,2λ5,4λ5,6λ5-triazatriphosphorine-2,2-diamineThe crystal structure of the geminal isomer of N3P3F4(NH2)2 (3) was determined by X-ray analysis and was refined to R = 0.035. Crystals of the compound are orthorhombic, space group Pnma. The six-membered (P—N)3 ring is planar within the limits of error. In the (NH2)2 P—N—P(F2) segment the P—N bond lengths are 1.597 and 1.524Å with the shorter one on the side of the PF2 group. In the (F2)P—N—P(F2) segment the P—N bond length is 1.564 Å. The mean bond lengths in each P—N—P segment are nearly equal. The mean values for the P—F and P—Namine bond lengths were found to be 1.532 and 1.602 Å, respectively. The endocyclic angles are: N—P—N 110.4°, 120.5°; P—N—P 125.7°, 117.2°.
    Notes: Die Struktur des geminalen N3P3F4(NH2)2 (3) wurde aus Röntgenbeugungsdaten bestimmt und zu einem R-Wert von 3.5% verfeinert. Die Verbindung kristallisiert orthorhombisch in der Raumgruppe Pnma. Der (P—N)3-Ring ist innerhalb der Fehlergrenzen planar. Die P—N-Abstände betragen im (NH2)2 P—N—P(F2)-Segment 1.597 und 1.524 Å mit dem kürzeren Abstand auf der Seite der PF2-Gruppe. Im (F2)P—N—P(F2)-Segment ergibt sich die P—N-Bindungslänge zu 1.564 Å. Damit sind die Mittelwerte der Bindungslängen in jedem P—N—P-Segment nahezu gleich groß. Die Mittelwerte für die P—F- und die P—NAmin-Bindungslängen betragen 1.532 bzw. 1.602 Å. Die N—P—N-Winkel im Ring wurden zu 110.4° und 120.5°, die P—N—P-Winkel zu 125.7° und 117.2° beobachtet.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 110 (1977), S. 3183-3189 
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: The Crystal and Molecular Structure of [Bis(trimethylsilyl)amino]-bis(trimethylsilylimino)phosphoraneThe crystal structure of the title compound 1 was determined from single crystal X-ray data (measured at +18 and -130°C) and was refined to R = 0.043 (-130°C). The compound crystallizes in the monoclinic space group C2/c. Comparison of bond lengths in 1 at the two temperatures demonstrates the necessity of a correction for shortening due to thermal motion for the SiR3-groups (R = methyl). The planar threefold nitrogen coordination of the phosphorus seems to favor the assumption of pπ-pπ-bonds. The P-Nimine and P-Namine bond lengths were found to be 1.515 and 1.638 Å, respectively; Nimine-Si 1.703, Namine-Si 1.787 Å, angle P = N-Si 146.8° (all values for -130°C).
    Notes: Die Struktur der Titelverbindung 1 wurde aus bei + 18 und - 130°C ermittelten Diffraktometer-Einkristalldaten bestimmt und zu einem R-Wert von 4.3% (-130°C) verfeinert. Die Verbindung kristallisiert monoklin in der Raumgruppe C2/c. Z = 4. Ein Vergleich der Bindungslängen in 1 bei den verschiedenen Temperaturen zeigt für die endständigen Trimethylsilylgruppen die Notwendigkeit einer Korrektur der durch thermische Schwingungen scheinbar verkürzten Abstände. Das zentrale Phosphoratom weist eine planare dreifache Koordination von Stickstoffatomen auf. Bindungslängen und die Symmetrie des Moleküls deuten auf die Existenz von pπ-pπ-Bindungen zwischen Phosphor und Stickstoff hin. Der P-NImin-Abstand beträgt 1.515, der P-NAmin-Abstand 1.638 Å. Die NImin-Si- und NAmin-Si-Bindungslängen wurden zu 1.703 bzw. 1.787 Å beobachtet. Der P = N-Si-Winkel beträgt 146.8° (alle Werte für -130°C).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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