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21 results on '"Zippel, Frank"'

1. Aqua complexes of ((2-methoxyethyl)cyclopentadienyl)zirconium trichloride

Author

van der Zeijden, Adolphus A.H., Mattheis, Chris, Frohlich, Roland, and Zippel, Frank

Subjects
Ligands -- Research, Complex compounds -- Research, Cyclic compounds -- Research, Coordination compounds -- Research, Chemistry
Abstract

The reaction of ((eta5:eta1-C5H4CH2CH2OMe)ZrCl2(mu-Cl))2 (1) with several solvents, particularly with water, was studied. The bidentate coordination of the C5H4CH2CH2OMe ligand in 1 was retained chloroform, dichloromethane, benzene, acetone, thf and acetonitrile. The coordination of the ether side chain was reversibly broken in methanol and water. A thf solvate of 1 was structurally analyzed. Reaction of wet DMSO produced the salt ((eta5:eta1-C5H4CH2CH2OMe)ZrCl2(H2O)(DMSO)2)(C) in which the ether side-arm was not coordinated.

Published
1997

2. Structural and functional models for the dinuclear copper active site in catechol oxidases: syntheses, X-ray crystal structures, magnetic and spectral properties, and X-ray absorption spectroscopic studies in solid state and in solution

Author

Zippel, Frank, Ahlers, Friedhelm, Werner, Rudiger, Hasse, Wolfgang, Nolting, Hans-Friedrich, and Krebs, Bernt

Subjects
Copper compounds -- Analysis, Molecular structure -- Analysis, Oxidation-reduction reaction -- Analysis, Chemistry
Abstract

Dinuclear copper complexes containing tridentate dinucleating ligands are prepared and considered as structural and functional models for catechol oxidases. In these complexes, the Cu(II) centers undergo antiferromagnetic coupling. The crystal structure of the complexes remain unchanged in the methanolic solution. The copper complex of 1,5-bis(2-benzimidazolyl)-3-pentanol exhibits catecholase activity by oxidizing 3,5-di-tert-butylcatechol to quinone.

Published
1996

19. Substituent-Dependent Formation of Supramolecular Aggregates of 6-Hydroxy-<BI>trans</BI>-3-hexenoic Acids in the Solid State

Author

Strauch, Hans Christian, Rinderknecht, Thomas, Erker, Gerhard, Fröhlich, Roland, Wegelius, Elina, Zippel, Frank, Höppener, Stephanie, Fuchs, Harald, and Chi, Lifeng

Abstract

The substituted 6-hydroxy-trans-3-hexenoic acids 2-4 have been prepared by a template coupling reaction between (butadiene)zirconocene, W(CO)6, and cyclobutanone, cyclodecanone, or cyclododecanone, respectively, followed by hydrolytic/oxidative demetallation of the resulting metallacyclic zirconoxycarbene tungsten complexes. The hydroxyalkenoic acids 2-4 have been found to form two novel fundamental types of associated supramolecular structural arrays in the solid state through intermolecular hydrogen bonding, which have been characterized by X-ray diffraction analysis. The cyclobutanone-derived compound 2 exhibits an infinitely extending sheet-like structure, which is composed of symmetrically alternating interconnected 12- and 36-membered rings, each being constructed from the functional groups or frameworks of four individual molecules of 2. In contrast, the cyclodecanone-derived compound 3 adopts a ribbon-type structure composed of C2-symmetrically arranged symmetry-equivalent 15-membered rings, each containing the functionalities from three individual molecules of 2. On the basis of scanning force microscopy studies, the cyclododecanone-derived compound 4 would appear to have a similar structure in the solid state. The structural features of the molecular assemblies that are formed by intermolecular hydrogen bonding of compounds 2-4 in the solid state are selectively controlled by the size and favoured conformations of the spiro-anellated carbocyclic rings at C6 of the 6-hydroxy-trans-3-hexenoic acid carbon chain.

Published
2000
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20. Biochemical and spectroscopic characterization of catechol oxidase from sweet potatoes (Ipomoea batatas) containing a type-3 dicopper center1In memoriam to Prof. Dr. Dr. H. Witzel.1

Author

Eicken, Christoph, Zippel, Frank, Büldt-Karentzopoulos, Klaudia, and Krebs, Bernt

Subjects
EXAFS, N-terminal sequence, Catechol oxidase, Dicopper enzyme, Ipomoea batatas
Abstract

Two catechol oxidases have been isolated from sweet potatoes (Ipomoea batatas) and purified to homogeneity. The two isozymes have been characterized by EXAFS, EPR-, UV/Vis-spectroscopy, isoelectric focusing, and MALDI-MS and have been shown to contain a dinuclear copper center. Both are monomers with a molecular mass of 39 kDa and 40 kDa, respectively. Substrate specificity and NH2-terminal sequences have been determined. EXAFS data for the 39 kDa enzyme reveal a coordination number of four for each Cu in the resting form and suggest a Cu(II)-Cu(II) distance of 2.9 Å for the native met form and 3.8 Å for the oxy form.

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21. Formation of Group 4 Metallocene‐Enolate⋅B(C6F5)3Adducts and Their Role as Initiators in the Rapid Polymerization of the Functionalized Olefin Methyl vinyl ketone

Author

Spaether, Wolf, Klaß, Katrin, Erker, Gerhard, Zippel, Frank, and Fröhlich, Roland

Abstract

The strong Lewis acid B(C6F5)3adds to the bis(enolate)‐Group 4 metallocenes 1to give the adducts 2. Complex 1/B(C6F5)3mixtures, especially in an overstoichiometric ratio, provide very active catalysts for the polymerization of methyl vinyl ketone.

Published
1998
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