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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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Journal ArticleDOI
TL;DR: In this article, the NMR and X-ray data of B2S3 glass was used to obtain detailed information about the structural units and the precipitation of crystalline phases.
Abstract: 11B, 203Tl and 205Tl NMR studies of glasses in the system Tl2SB2S3 have shown striking similarities to borate glasses. For low thallium contents, the fraction N4 of four-coordinated boron atoms increases in proportion to R = mol.% Tl2S/mol.% B2S3, and the monovalent thallium is tetrahedrally coordinated by sulfur. N4 reaches a maximum near R = 0.5, and discontinuous changes of the thallium bonding state towards more covalency is indicated at high Tl contents. Detailed information about the structural units and the precipitation of crystalline phases is obtained from the NMR and X-ray data. Differences between oxide and non-oxide systems are discussed.

23 citations

Journal ArticleDOI
TL;DR: Purple acid phosphatase from red kidney bean has been crystallized from ammonium sulfate solutions in the pH range from 3.5 to 5.5 and the crystal form is tetragonal bipyramidal and the largest crystals grew up to 2.0 mm long.

23 citations

Journal ArticleDOI
01 Nov 1989
TL;DR: In this article, Li NMR spin-lattice relaxation rates at 16 MHz and 117 MHz have been measured at various temperatures for glasses in the nonoxide chalcogenide system B 2 S 3 -Li 2 S-LiX with X=Cl, Br, I.
Abstract: 7 Li NMR spin-lattice relaxation rates at 16 MHz and 117 MHz have been measured at various temperatures for glasses in the non-oxide chalcogenide system B 2 S 3 -Li 2 S-LiX with X=Cl, Br, I. As compared with the corresponding oxide glasses these materials are distinguished by a higher ionic conductivity, and the relaxation maxima are better accessible. The relaxation rates display anomalous temperature and frequency dependences. Attempts to interpret the non-BPP-type relaxation in terms of appropriate diffusion models are discussed

23 citations

Journal ArticleDOI
TL;DR: In this article, the addition of secondary phosphanes PHR26 to 1 affords red (2-phosphanyl ethenyl)-carbene complexes (CO)5MC(OEt)-CHC(R)-PR2 (E)-8 (R = tBu, cC6H11, Ph) in 34-89% isolated yields.
Abstract: Alkynylcarbene complexes (CO)5MC(OEt)-C≡CR 1 (M = Cr, W; R = Ph, tBu, SiMe3) readily add tertiary phosphanes PPhR2′ 4 (R′ = Ph, Me) to form stable zwitterionic phosphonium allenide complexes (CO)5M--C(OEt) = CC(R)-P+PhR2′ 5. Complex 5a (M = Cr, R = R′ = Ph) was characterized by X-ray diffraction. The addition of secondary phosphanes PHR26 to 1 affords red (2-phosphanyl ethenyl)-carbene complexes (CO)5MC(OEt)-CHC(R)-PR2 (E)-8 (R = tBu, cC6H11, Ph) in 34–89% isolated yields. Dinuclear complexes (CO)5MC(OEt)-CHC(R)-P(R2)M(CO)5 (E)-9 are obtained as byproducts. Compounds (E)-8b (M = Cr, R = cC6H11) and (E)-9i (M = Cr, R = Ph) were characterized by X-ray analyses.

23 citations


Cited by
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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

Journal ArticleDOI
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