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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.


Papers
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TL;DR: The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C as mentioned in this paper.
Abstract: Systematic studies on selenoborates containing a B12 cluster entity and alkali metal cations led to the new crystalline phase Na8[B12(BSe3)6] which consists of a icosahedral B12 cluster completely saturated with trigonal-planar BSe3 units and sodium counter-ions. The new chalcogenoborate was prepared in a solid state reaction from sodium selenide, amorphous boron and selenium in evacuated carbon coated silica tubes at a temperature of 850 °C. Na8[B12(BSe3)6] crystallizes in the monoclinic space group P21/c (no. 14) with a = 10.990(1) A, b = 16.279(1) A, c = 11.490(1), β = 117.82(1)° and Z = 2. Na8[B12(BSe3)6]: Ein neues Selenoborato-closo-dodecaborat Gezielte Versuche zur Synthese neuer Selenoborato-closo-dodecaborate fuhrten im ternaren Phasengebiet Na/B/Se zu der neuen Verbindung Na8[B12(BSe3)6], in der ein vollstandig durch Chalkogenatome abgesattigtes B12-Ikosaeder vorliegt. Das neue Chalkogenoborat wurde in einer Hochtemperatur-Feststoffreaktion aus Natriumselenid, amorphem Bor und Selen in graphitierten, evakuierten Quarzglasampullen hergestellt. Na8[B12(BSe3)6] kristallisiert in der monoklinen Raumgruppe P21/c (Nr. 14) mit a = 10, 990(1) A, b = 16, 279(1) A, c = 11, 490(1), β = 117, 82(1)° und Z = 2.

8 citations

Journal ArticleDOI
TL;DR: In this paper, the infrared absorption frequencies of crystalline Ni(NH3)3CS3, Ni(ND3), 3CS3 and Zn(NH 3)2CS3 between 4000 and 300 cm-1 are tabulated.
Abstract: The infrared absorption frequencies of crystalline Ni(NH3)3CS3, Ni(ND3)3CS3, Zn(NH3)2CS3, and Zn(ND3)2CS3 between 4000 and 300 cm-1 are tabulated. The absorption bands corresponding to the fundamental vibrations are assigned. The positions of the bands are discussed in comparison with spectra of other ammine complexes and of non-complex trithiocarbonates.

8 citations

Journal Article
TL;DR: In this paper, three tricyclic platinum compounds, aminoplatin, methylplatin and oxiplatin, were compared in three human glioma cell lines (T98G, U87-MG, and U25 IN) and a human fibroblast cell strain (HS 68).
Abstract: Background: Cisplatin (CDDP) is a very useful chemotherapeutic agent, but cellular resistance limits its efficacy in malignant glioma. In order to analyze and overcome this resistance, we synthesized three novel platinum compounds; aminoplatin, methylplatin and oxiplatin, using tricyclic DNA intercalating molecules as models. Materials and Methods: The novel compounds differ only in one chemical group, which is positioned opposite to the DNA binding site. DNA binding, cellular penetration, and cytotoxicity were compared in three human glioma cell lines (T98G, U87-MG, and U25 IN) and a human fibroblast cell strain (HS 68). 2 Result: Binding to isolated DNA was most effective in aminoplatin, followed by methylplatin and oxiplatin. It differed by factors I. I, 0.35, 0.23, from the DNA binding of CDDP (factor I) for the three compounds, respectively. The cellular penetration, however, was fastest with oxiplatin (factor 10.1) followed by CDDP (1), aminoplatin (0.55), and methylplatin (0.27). The cytotoxicity of the three novel compounds followed the pattern of their cellular penetration with oxiplatin being the most active. U87-MG cells were resistant to CDDP, and in this cell line oxiplatin was more effective than CDDP in overcoming the resistance. Conclusion: This indicates cellular penetration to he an important feature and the ketogroup of oxiplatin to be beneficial in tricyclic platinum compounds.

8 citations


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TL;DR: 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.
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)

10,126 citations

Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
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

9,929 citations

Journal ArticleDOI
TL;DR: The hydrogen bond is the most important of all directional intermolecular interactions, operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological.
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.

5,153 citations

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TL;DR: The transition metal dichalcogenides are about 60 in number as discussed by the authors, and two-thirds of these assume layer structures and can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions.
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.

3,313 citations

Journal ArticleDOI
TL;DR: 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 or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers.
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.

3,241 citations