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)

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The chemistry of graphene oxide

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

Phd by thesis

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 hydrogen bond in the solid state.

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.

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

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.

Multicopper Oxidases and Oxygenases

Die aus wasriger Losung durch Reaktion von As2O3 mit NaOH und Selen (oder durch Umsetzung von Na2Se mit As2Se3 und Selen) unter strengem Sauerstoffausschlus zuganglichen farblosen kristallwasserhaltigen Selenoarsenate enthalten neben den tetraedrischen Anionen AsO3Se3− und AsSe43− Wasserstoffbrucken-Systeme mit strukturbestimmenden OH … Se- Brucken. Na3AsO3Se · 12 H2O kristallisiert in P212121 mit a = 9,220(3), b = 13,018(3), c = 14,048(4) A, Z = 4. Das kubische Na3AsSe4 · 9 H2O (P213, a = 12,149(3) A, Z = 4) ist isotyp mit dem Schlippeschen Salz Na3SbS4 · 9 H2O. Die Se2− in AsO3Se3− und AsSe43− sind H-Acceptoren in jeweils 6 Se … HO-Wasserstoffbrucken mit d(Se…O) = 3,693 A und d(Se…H) = 2,47–2,89 A. Die AsSe-Bindung in AsO3Se3− (2,283 A) ist kurzer als bei AsSe43− (2,319 A).

Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O†

Na6[B18Se17]: The First Selenoborato-closo-dodecaborate with a Polymeric Chain Anion

A test of the ability of extended X-ray absorption fine structure (EXAFS) to determine structural information with specific reference to zinc sites in enzymes has been made. X-ray absorption spectra of 18 compounds of zinc have been measured and the nearest-neighbour scattering has been interpreted using a Fourier transform and an ab initio technique. Empirical Zn-N, Zn-O, Zn-S and Zn-Cl amplitude and phase functions have been extracted from Zn(C3H4N2)4(ClO4)2, ZnO, Zn(S2COC2H5)2 and [N(CH3)4]2[ZnCl4], respectively and tabulated as a function of the wavevector with respect to 9660.0 eV X-ray energy. These amplitude and phase functions were then tested with respect to the other 14 compounds. For a single species of atoms in the first coordination shell the interatomic distances can be established to +/- 0.5 pm (+/- 5 x 10(-3) A) whilst when mixed shells exist errors in distances are +/-4 pm (+/- 40 x 10(-3) A). Coordination numbers are given to +/- 16% for the single species case a and +/- 25% for the mixed coordination case. Using the theoretical amplitude and phase functions of McKale et al. [(1988) J. Am. Chem. Soc. 110, 3763-3768] the deduced distances are systematically too small by an average of 0.6 pm (6 x 10(-3) A). The errors in the coordination numbers are 18%.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1989.tb15258.x

Extended X‐ray absorption fine structure (EXAFS) investigations of model compounds for zinc enzymes

Selenoboratoborate [B12(BSe3)6]8−: eine neue Klasse chalkogensubstituierter ikosaedrischer Borcluster

Starting from the tripodal tetradentate ligands -(3,5-dibromo-2-hydroxybenzyl)(2-hydroxybenzyl)(2-pyridyl)methylamine (H2L1), (3,5-dibromo-2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L2), and (3,5-dichloro2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L3) the new isostructural dinuclear zinc compounds [Zn2(L1)2]·N(CH2CH3)3 (1), [Zn2(L2)2]·2CH3OH (2) and [Zn2(L3)2]·C4H10O (3) were synthesized. Due to their enzyme-like trigonal bipyramidal N2O3 coordination environment of the zinc ions and the similar Zn···Zn distances the complexes can be considered to be structural models for the active sites in phospholipase C and nuclease P1. With H2L3 also the dinuclear complex [Co2(L2)2(CH3OH)]·2CH3OH·0.5C4H10O (4) could be prepared.



The new compounds were isolated and characterized by single crystal X-ray crystallography as well as infrared spectroscopy. The cobalt compound 4 was additionally characterized by UV-Vis spectroscopy and magnetic measurements. 1 crystallizes in the monoclinic space group P21/n with a = 11.2814(2), b = 28.6154(2), c = 13.1866(3) A, β = 96.995(1)°, V = 4225.2(2) A3, Z = 4. 2 and 3 are monoclinic, space group C2/c with a = 23.084(5), b = 9.232(2), c = 21.849(4) A, &β; = 96.83(3)°, V = 4623(2) A3, Z = 4, and a = 22.7834(3), b = 9.2463(1), c = 21.6351(3) A, &β; = 97.592(1)°, V = 4517.7(2) A3, Z = 4, respectively. 4 crystallizes in the monoclinic space group I2/a with a = 22.4680(4), b = 20.5517(4), c = 22.8910(6) A, &β; = 111.938(1)°, V = 9804.7(4) A3, Z = 8. 4 shows an effective magnetic moment of 6.72 μB at 300 K which clearly indicates the presence of two cobalt(II) high spin ions with Curie-Weiss behaviour above 80 K. At lower temperatures a decrease of the effective magnetic moment was observed.

Bernt Krebs

Papers

Selenoarsenate aus wäßriger Lösung. Die Kristallstruktur von Na3AsO3Se · 12 H2O und Na3AsSe4 · 9H2O†

Na6[B18Se17]: The First Selenoborato-closo-dodecaborate with a Polymeric Chain Anion

Extended X‐ray absorption fine structure (EXAFS) investigations of model compounds for zinc enzymes

Selenoboratoborate [B12(BSe3)6]8−: eine neue Klasse chalkogensubstituierter ikosaedrischer Borcluster

Zinc and Cobalt Complexes Derived from Tetradentate Tripodal Ligands with N2O2 Donorset as Model Compounds for Phosphatases