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  • Chemistry  (29)
  • 42.20  (2)
  • 65.40.−f  (2)
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  • 1
    Digitale Medien
    Digitale Medien
    The quadrupolar and hyperfine splittings in the metal cluster compound Au55(PPh3)12Cl6 (1993)
    Springer
    The European physical journal 26 (1993), S. 27-29 
    Details
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 65.40.−f ; 76.80.+y
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract There are 5 different Au-sites in the Au55 core of Au55(PPh3)12Cl6. The 13 inner atoms are almost identical to that of bulk gold. At the surface the attachment of the ligands is responsible for further differentiation. We have calculated the low temperature specific heat using the Mössbauer determined electrical quadrupolar splitting of the surface atoms. Due to too long a quadrupolar relaxation time, no such contribution is seen in the zero field results (down to 0.06 K) of Goll et al., Z. Phys. D 20, 329 (1991). The latter zero and in-field data are interpreted as the contribution of an electronic spin, hyperfine coupled to a nuclear spin 3/2. The effective abundance is about one spin per ten clusters.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01425607
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  • 2
    Digitale Medien
    Digitale Medien
    Characterization of a cellodextrin glucohydrolase with soluble oligomeric substrates: Experimental results and modeling of concentration-time-course data (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 33 (1989), S. 1445-1460 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A previously isolated cellodextrin glucohydrolase (β-glucosidase) from Trichoderma reesei QM 9414 is characterized using β-1,4-glucose oligomers with defined degrees of polymerization as soluble substrates. The enzyme splits off glucose units from the nonreducing chain ends of cellooligomers. Besides this hydrolytic activity there is also evidence for transfer activity depending on the concentration and degree of polymerization of substrates. Concentration-time-course data have been gathered for the degradation of cellobiose, cellotriose, cellotetraose, cellopentaose, and cellohexaose covering a wide range of enzyme and substrate concentrations. A Michaelis-Menten type kinetic model has been developed, which is able to satisfactorily describe the complex system of parallel and series reactions during the conversion of oligomers to glucose. The only kind of inhibition considered is competitive inhibition by the final product glucose. The model takes into account the formation of multiple enzyme-substrate complexes and is limited to those conditions, in which no transglucosylation products are observed. Cellodextrins with higher degrees of polymerization are found to be better substrates for this enzyme than is the dimer cellobiose.
    Zusätzliches Material: 12 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260331112
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  • 3
    Digitale Medien
    Digitale Medien
    Purification and partial characterization of a cellodextrin glucohydrolase (β-glucosidase) from Trichoderma reesei strain QM 9414 (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 30 (1987), S. 571-585 
    Details
    ISSN: 0006-3592
    Schlagwort(e): Chemistry ; Biochemistry and Biotechnology
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Biologie , Werkstoffwissenschaften, Fertigungsverfahren, Fertigung
    Notizen: A β-glucosidase (E.C. 3.2.1.21) was isolated from the culture filtrate of fungus Trichoderma reesei QM 9414 grown in continuous culture with biomass retention. The crude extracellular enzyme preparation was fractionated by a three-step purification procedure [chromatography on Fractogel HW-55 (S) and Bio-Gel A 0.5 plus final preparative isoelectric focusing] to yield three β-glucosidases with isoelectric points at pH 8.4, 8.0, and 7.4. Only one enzyme (pi 8.4) met the stringent criterion of being homogeneous according to titration curve analysis. This enzyme was then characterized not to be a glycoprotein, although the native protein contained 35% carbohydrate (as glucose). It was found to have an apparent molar mass of 7 × 104 g/mol (SDS-PAGE), exhibited its optimum activity towards cellobiose at pH 4.5 and 70°C (30 min test), and lost less than 3% activity at 50°C over a period of 7 h. The KM values towards cellobiose and p-nitrophenyl-β-D-glucopyranoside were determined to be 0.5mM and 0.3mM, respectively. The enzyme hydrolyzed cellodextrins (cellotriose to cellooctaose) by sequentially splitting off glucose units from the nonreducing end of the oligomers. The extent of the observed transfer reactions varied with the initial substrate concentration. No enzyme activity towards microcrystalline cellulose or carboxymethylcellulose could be detected. The classification of the enzyme as β-glucosidase or exo-β-1,4-glucan glucohydrolase is discussed with respect to the exhibited hydrolytic activities.
    Zusätzliches Material: 11 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/bit.260300415
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  • 4
    Digitale Medien
    Digitale Medien
    Optical plasmon losses in stabilized Au55 clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 297-300 
    Details
    ISSN: 1434-6079
    Schlagwort(e): 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Au55 cluster compounds are investigated by optical spectroscopy and TEM. The optical spectra appear to be rather structureless, neither showing a collective excitation resonance nor exhibiting distinct absorption bands known from lower nuclearity clusters. We discuss changes of the electronic properties compared to larger Au clusters affecting both, 6sp electrons and5d-6sp interband transitions, the cluster-ligand-interaction being considered as a charge transfer process. We additionally report on a low temperature instability of the cluster compound, which results in changed optical extinction spectra. A characteristic absorption feature at λ=400 nm is attributed to small, ligand-free Au cluster fragments.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01543995
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  • 5
    Digitale Medien
    Digitale Medien
    Low-temperature specific heat of the cluster compound Au55 (P(C6H5)3)12Cl6 (1991)
    Springer
    The European physical journal 20 (1991), S. 329-331 
    Details
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 65.40.−f
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Specific-heat measurements on the cluster compound Au55(P(C6H5)3)12Cl6 at temperatures 0.06 K ≤T≤3 K and in magnetic fields 0≤B≤6 T are reported. While above 0.6 K the specific heatC is dominated by the inter-cluster vibrational contribution observed previously, an anomalous increase ofC towards lowT is observed below 0.3 K, withC ∼T −2. This contribution develops into a Schottky-like anomaly forB≥0.4 T, indicating that it might be attributed to local moments which are also observed in ESR measurements. From the height of the anomaly one can infer that approximately one tenth of the Au55 clusters carry a magnetic moment. For 0.6 K≤T≤1 K andB=0 our data indicate the absence of a linear electronic specific-heat contribution expected for bulk Au. This possibly constitutes the first direct observation of the quantum-size effect on electronic energy levels in the specific heat.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01544003
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  • 6
    Digitale Medien
    Digitale Medien
    Optical properties of systems containing Au55-clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 515-520 
    Details
    ISSN: 1434-6079
    Schlagwort(e): 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Gold cluster compounds were investigated which contain clusters of 55 gold atoms in each unit. The ligands stabilize these clusters and, hence, many-cluster systems can be prepared which mainly show the properties of the single dressed cluster. Experimental results of optical and electron-microscopical investigations are presented and shortly discussed in view of the question whether the clusters are molecular or solid-state like.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01427009
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  • 7
    Digitale Medien
    Digitale Medien
    P2J3 - ein neuartiger KomplexligandProfessor Carl Mahr zum 75. Geburtstage am 22. Dezember 1975 gewidmet. (1975)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 418 (1975), S. 243-246 
    Details
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: P2J3 - a New Complex LigandP2J4 and Na2Cr(CO)5 react in benzene to the monomeric diamagnetic complex (CO)4CrP2J3. The 31P-nmr spectrum shows the presence of different bonded phosphorus atoms. The exchange of one iodine atom between the P atoms leads to a temperature dependent equilibrium with a symmetrical transition state. Triphenyl- and tricyclohexylphosphine react with (CO)4CrP2J3 to (CO)4CrPJ2 · P(C6H5)3 resp. (CO)4CrPJ2 · P(C6H11)3, probably of dimeric nature.
    Notizen: P2J4 und Na2Cr(CO)5 reagieren in Benzol zu dem monomeren, diamagnetischen Komplex (CO)4CrP2J3. Das 31P-NMR-Spektrum zeigt die Anwesenheit unterschiedlich gebundener Phosphoratome. Der Austausch eines Jodatoms zwischen den P-Atomen führt zu einem temperaturabhängigen Gleichgewicht, in dem ein symmetrischer Übergangszustand auftritt. Triphenyl- und Tricyclohexylphosphin reagieren mit (CO)4CrP2J3 zu (CO)4 · P(C6H5)3 bzw. (CO)4 CrPJ2 · P(C6H11)3, wahrscheinlich dimerer Natur.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/zaac.19754180307
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  • 8
    Digitale Medien
    Digitale Medien
    Versuche zur Oxydativen Addition von Thionylhalogeniden an Übergangsmetallkomplexe (1975)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 415 (1975), S. 97-103 
    Details
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: Experiments on the Oxidative Addition of Thionylhalides to Transition Metal ComplexesThe complexes [(C6H5)3P]4Pd and [(C6H5)3P]2Ni(NO)Cl react with SOX2 to trans [(C6H5)3P]2PdX2 (X = Cl, Br) resp. to [(C6H5)3PX][NiX3] (X = Cl). Furthermore (C6H5)3PO and (C6H5)3PS are formed. In contrast SOCl2 is added oxidatively by [(C6H5)3P]2Ir(CO)Cl to the complex [(C6H5)3P]2Ir(CO)(Cl2)SOCl.
    Notizen: Die Komplexe [(C6H5)3P]4Pd und [(C6H5)3P]2Ni(NO)Cl reagieren mit SOX2 zu trans-[(C6H5)3P]2PdX2 (X = Cl. Br) bzw. [(C6H5)3PX][NiX3] (X = Cl). Weiterhin bilden sich (C6H5)3PO und (C6H5)3PS. Im Gegensatz dazu wird SOCl2 durch [(C6H5)3P]2 Ir(CO)Cl oxydativ zu dem Komplex [(C6H5)3P]2 Ir(CO)(Cl2)SOCl addiert.
    Zusätzliches Material: 1 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/zaac.19754150202
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  • 9
    Digitale Medien
    Digitale Medien
    Die Verwendung von Elementarem Phosphor als Ligand in Eisencarbonylen (1977)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 432 (1977), S. 160-166 
    Details
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: The Use of Elemental Phosphorus as Ligand in Iron CarbonylsWhite phosphorus and Fe2(CO)9 react in benzene at room temperature to the monomeric diamagnetic complex [(CO)4Fe]3P4. The Mössbauer spectrum proves the presence of penta- and hexacoordinated Fe atoms in the ratio 1:2. The i.r. spectrum also suggests different bonded Fe(CO)4 groups. As the 31P-n.m.r. spectrum shows, the 4 P atoms are equivalent. It is supposed that one Fe(CO)4 group fluctuates between the P atoms. At 70°C P4 and Fe2(CO)9 react to the polymeric diphosphorous complex [(CO)3FeP2]n. Its synthesis succeeds also with Fe(CO)5 and P4 under u.v. irradiation. Additionally [(CO)4Fe]3P4 can be decomposed to [(CO)3FeP2]n by warming or irradiation. The Mössbauer spectrum of this complex shows equivalent Fe atoms with the coordination number 6. Possible structures are discussed.
    Notizen: Weißer Phosphor und Fe2(CO)9 reagieren in Benzol bei Raumtemperatur zu dem monomeren, diamagnetischen Komplex [(CO)4Fe]3P4. Das Mössbauerspektrum belegt die Anwesenheit fünffach und sechsfach koordinierter Fe-Atome im Verhältnis 1:2. Auch das IR-Spektrum legt unterschiedlich gebundene Fe(CO)4-Gruppen nahe. Wie das 31P-NMR-Spektrum zeigt, sind alle 4 P-Atome äquivalent. Es wird angenommen, daß eine Fe(CO)4-Gruppe zwischen den P-Atomen fluktuiert. Bei 70°C setzen sich P4 und Fe2(CO)9 zu dem polymeren Diphosphorkomplex [(CO)3FeP2]n um. Dessen Synthese gelingt auch aus Fe(CO)5 und P4 unter UV-Bestrahlung. Ebenso kann [(CO)4Fe]3P4 durch Erwärmen oder Belichten in [(CO)3FeP2]n zersetzt werden. Das Mössbauerspektrum dieses Komplexes zeigt äquivalente Fe-Atome mit der Koordinationszahl 6. Mögliche Strukturen werden diskutiert.
    Zusätzliches Material: 5 Ill.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/zaac.19774320121
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  • 10
    Digitale Medien
    Digitale Medien
    Metall-Bor-Verbindungen. III. Über Triphenylphosphin-tetracarbonylmangan-Bor-VerbindungenProfessor E. Wiberg zum 65. Geburtstage am 3. Juni 1966 gewidmet (1966)
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 345 (1966), S. 69-78 
    Details
    ISSN: 0044-2313
    Schlagwort(e): Chemistry ; Inorganic Chemistry
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Beschreibung / Inhaltsverzeichnis: A hypothesis is presented on the formation of stable covalent metal boron bonds in molecular compounds, and the synthesis of X2B—Mn(CO)4P(C6H5)3 and XB[Mn(CO)4P(C6H5)3]2 (X = C6H5, C4H9, Cl, NR2, OCH3) is described. These compounds are more stable than the corresponding Mn(CO)5-derivatives. This is attributed to differences in the electron density at the manganese atom. 11B - NMR studies are interpreted in terms of back-donation of metal d-electrons to the tervalent boron atom.
    Notizen: Nach kurzer Erörterung einiger Leitgedanken, die dem Aufbau kovalenter Bor - Metall Bindungen in molekularen Verbindungen zugrunde liegen, wird die Synthese von X2B—Mn(CO)4P(C6H5)3 und XB[Mn(CO)4P(C6H5)3]2 (X = C6H5, C4H9, Cl, NR2, OCH3) beschrieben. Diese Verbindungen sind stabiler als die entsprechenden Mn(CO)5-Derivate, was wahrscheinlich auf Unterschieden in der Elektronendichte an den Manganatomen beruht. 11B-kernresonanzspektroskopische Untersuchungen weisen auf eine Beteiligung der Metall-d-Elektronen an der Mangan--Bor-Bindung hin.
    Zusätzliches Material: 3 Tab.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1002/zaac.19663450109
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