Bernt Krebs

Bio: Bernt Krebs is an academic researcher from University of Münster. The author has contributed to research in topics: Crystal structure & Ligand. The author has an hindex of 56, co-authored 729 publications receiving 16336 citations. Previous affiliations of Bernt Krebs include Leiden University & Clariant.

Alternativ-Liganden. XXVI [1]. M(CO)4L-Komplexe (M Cr, Mo, W) der Chelatliganden Me2ESiMe2(CH2)2E′Me2 (Me CH3; E P, As; E′ N, P, As)†

Abstract: Die Umsetzung von M(CO)4NBD (NBD = Norbornadien; M Cr, Mo, W) mit den Liganden Me2ESiMe2(CH2)2E′Me2 liefert fur E,E′ P, As die Chelatkomplexe (CO)4M[Me2ESiMe2(CH2)2E′Me 2], nicht jedoch fur E und/oder E′ N. Die NSi-Gruppierung ist wegen der starken (p-d)π-Ruckbindung nicht zur Koordination befahigt; im Fall der Liganden mit E P oder As und E′ N sind im Reaktionsgemisch zwar Chelatkomplexe nachweisbar, bei den isolierbaren Produkten handelt es sich jedoch um Komplexe mit zwei E-koordinierten Liganden. Die neuen Verbindungen werden durch analytische und spektroskopische (IR, NMR, MS) Untersuchungen charakterisiert. Die spektroskopischen Daten dienen auch der Beurteilung der Koordinations-eigenschaften der Liganden. Die Rontgenbeugungsanalyse der Molybdankomplexe (CO)4Mo[Me2ESiMe2(CH2) 2AsMe2] (E P, As) ergibt in Ubereinstimmung mit den Koordinationseffekten nur geringe Unterschiede zwischen SiE und CE-Donorfunktionen. – Bei Versuchen, die Liganden Me2ESiMe2(CH2)2AsMe2 (E P, As zur Synthese von Fe(CO)3L-Komplexen zu nutzen, werden unter Spaltung der SiE-Bindung die Zweikernsysteme Fe2(CO)6(EMe2)2(E P, As) und das Disilanderivat [Me2Si(CH2)2AsMe2]2 erhalten. Alternative Ligands. XXVI. M(CO)4 L-Complexes (M Cr, Mo, W) of the Chelating Ligands Me2ESiMe2(CH2)2E′ Me2 (Me CH3; E P, As; E′ N, P, As) The reaction of M(CO)4NBD (NBD = norbornadiene; M Cr, Mo, W) with the ligands Me2ESiMe2(CH2)2E′ Me2 yields the chelate complexes (CO)4M[Me2ESiMe2]) for E,E′ P, As, but not for E and /or E′ N. The NSi group is not suited for coordination because of strong (p-d)π-interaction. In the case of the ligands with E P or As and E′ N chelate complexes can be detected in the reaction mixture, but isolable products are complexes with two ligands coordinated via the E donor group. The new compounds are characterized by analytical and spectroscopic (IR, NMR, MS) investigations. The spectroscopic data are also used to deduce the coordinating properties of the ligands. X-ray diffraction studies of the molybdenum complexes (CO)4Mo[Me2ESiMe2(CH2)2AsMe 2] (E P, As) in accord with the observed coordination effects show only small differences between SiE and CE donor functions. Attempts to use the ligands Me2ESiMe2(CH2)2AsMe2 (E P, As) for the preparation of Fe(CO)3L complexes result in the fission of the SiE bonds and the formation of the binuclear systems Fe2(CO)6(EMe2)2 (E P, As) together with the disilane derivative [Me2Si(CH2)2AsMe2]2.

Method for producing macrocyclic monoepoxide having at least one double bond

Abstract: PROBLEM TO BE SOLVED: To provide a method for selectively epoxidizing one cis-double bond in a macrocyclic olefin. SOLUTION: This method comprises a catalytic selective epoxidation of a cis-double bond in a macrocyclic aliphatic hydrocarbon having 8-20 cyclic carbon atoms and having at least one trans-double bond and optionally at least one side chain; wherein the catalytic system comprises a phase-transfer catalyst and a polyoxometalate which consists of a tungsten- or molybdenum-based polyoxometalate and contains at least another group 14-16 element, and optionally contains at least one group 4-12 transition metal atom.

Polyoxoanions are cytotoxic to malignant glioma cells

Abstract: We studied the cytotoxicity of five polyoxoanions on two human malignant glioma cell lines (T98G and 86HG39), a rat glioma cell line (C6) and a human fibroblast cell line (NIH-3T3) using MTT tests to measure the drug concentration killing 50% of the cells (LC50). Cisplatin was used as a reference agent. Cisplatin had the highest efficacy in three of the four cell lines. Only in T98G cells, one of the components (POA5) had a lower LC50 value (1.3 x 10(-6) mol/l) than cisplatin (2.5 x 10(-6)). POA5 was also the most cytotoxic polyoxoanion when the LC50 values of all four cell lines were averaged (6.6 x10(-6)). Average LC50 values of the other compounds were 10.9, 12.6, 19.0 and 19.2 x 10(-6) mol/l in POA1, POA2, POA3 and POA4, respectively. When the benign fibroblasts were used to calculate a therapeutic index as LC50 in fibroblasts divided by LC50 in glioma cells, POA5 was superior to cisplatin. These results indicate that polyoxoanions are cytotoxic for malignant glioma cells and that the most promising compound investigated here was POA5.

The chemistry of graphene oxide

Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

The hydrogen bond in the solid state.

Abstract: The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties

Abstract: The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.

Multicopper Oxidases and Oxygenases

Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.