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.

Synthesis, structure and catecholase activity study of dinuclear copper(II) complexes†

Abstract: A series of dinuclear copper(II) complexes as models for the type 3 copper protein catechol oxidase were synthesised. They were characterised by spectroscopic, electrochemical, and in some cases, by single-crystal X-ray diffraction studies: [Cu2(L1)(OH)(EtOH)(H2O)][ClO4]2·H2O 1, [Cu2(L2)(OH)][NO3]22, [Cu2(L3)(OMe)(MeOH)(ClO4)]ClO43, [Cu2(L4)(OH)(MeOH)2][BF4]24, [Cu2(L5)(OMe)][ClO4]2·2MeOH 5, [Cu2(L6)(OMe)(MeOH)(ClO4)]ClO46 and [Cu2(L7)(OMe)(MeOH)(ClO4)]ClO47 (HL1 = 4-bromo-2,6-bis(4-methylpiperazin-1-ylmethyl)phenol, HL2 = 4-bromo-2,6-bis[(2-pyridylmethyl)aminomethyl]phenol, HL3 = 4-bromo-2,6-bis{[2-(2-pyridyl)ethyl]aminomethyl}phenol, HL4 = 4-bromo-2,6-bis{[2-(1-methyl-2-imidazolyl)ethyl]aminomethyl}phenol, HL5 = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-[(2-pyridylmethyl)aminomethyl]phenol, HL6 = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-{[2-(2-pyridyl)ethyl]aminomethyl}phenol and HL7 = 4-bromo-2-(4-methylpiperazin-1-ylmethyl)-6-{[2-(1-methyl-2-imidazolyl)ethyl]aminomethyl}phenol). The copper centres are µ-phenoxo bridged by the pentadentate dinucleating ligand and exogenously µ-hydroxo or µ-methanolato bridged. Complex 1 crystallises in P21/c with a = 16.913(3), b = 11.046(2), c = 16.617(3) A, β = 94.06(3)°, U = 3097 A3 and Z = 4. Complex 3 crystallises in P21/n with a = 10.592(2), b = 12.123(2), c = 24.482(5) A, β = 92.97(3)°, U = 3139 A3 and Z = 4. Complex 4 crystallises in Pbcn with a = 16.043(3), b = 12.689(3), c = 15.810(3) A, U = 3218 A3 and Z = 4. Complex 6 crystallises in P21/c with a = 17.889(4), b = 10.401(2), c = 16.269(4) A, β = 92.94(2)°, U = 3023 A3 and Z = 4. Complex 7 crystallises in P21/c with a = 17.349(3), b = 8.828(2), c = 19.797(4) A, β = 94.04(3)°, U = 3025 A3 and Z = 4. A catecholase activity study revealed that only complexes 1, 5, 6 and 7 have significant catalytic activity with respect to the aerial oxidation of 3,5-di-tert-butylcatechol. A kinetic treatment on the basis of the Michaelis–Menten model was applied.

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.

Abstract: Two novel tridentate dinucleating ligands containing benzimidazole were prepared, 1,3-bis(2-benzimidazolyl)-2-propanol (Hbbp, 1) and 1,5-bis(2-benzimidazolyl)-3-pentanol (Hbbpen, 2). Their complexing properties toward copper were studied in order to obtain structural and functional models for catechol oxidases. Syntheses and crystal structures of dinuclear Cu(II) complexes derived from these ligands are reported. [Cu2bbp2](ClO4)2·2MeOH, 3, crystallizes in the triclinic space group P1 with the following unit cell parameters: a = 7.702(3) A, b = 10.973(6) A, c = 12.396(6) A, α = 100.59(4)°, β = 99.02(4)°, γ = 98.90(4)°, V = 998.7(8) A3, and Z = 1. [Cu2bbpen2](ClO4)2·3MeOH, 4, crystallizes in the orthorhombic space group Pccn, with the following unit cell parameters: a = 17.478(9) A, b = 18.795(8) A, c = 13.888(6) A, V = 4562.2(4) A3, and Z = 4. Magnetic susceptibility measurements in the temperature ranges 4.6−459 K (3) and 4.6−425 K (4) indicate an antiferromagnetic coupling between the Cu(II) centers o...

Matrix‐assisted laser desorption/ionization mass spectrometry with additives to 2,5‐dihydroxybenzoic acid

Abstract: Selected benzoic acid derivatives and related substances were used as additives to 2,5-dihydroxybenzoic acid (2,5 DHB) and the performance of the mixtures in matrix-assisted laser desorption/ionization mass spectrometry was investigated. Using benzoic acid derivatives substituted at position 2 and /or 5 or related substances as a co-matrix in the 1-10% range with 2,5 DHB results in improved ion yields and signal-to-noise ratio of analyte molecules, especially for the high-mass range. The enhanced performance is prominent for 2-hydroxy-5 methoxybenzoic acid and exists for both proteins and oligosaccharides. It is suggested that the improvement is caused by a disorder in the 2,5 DHB crystal lattice allowing «softer» desorption. Charge transfer from matrix ions to additive molecules at the expense of analyte ionization gives a simple explanation for the deteriorating effects of some tested additives

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.