ZfN: Search Results

1	Author	DietrichM. Ootz, Dieter Stäben	Requires cookie*
	Title	Die Hydrate von terf-Butanol: Kristallstruktur von Me3COH * 2 H20 und Me3COH * 7 H20 [ 1 ]
	Abstract	The system /er/-butanol-water has been confirmed by X-ray powder diffraction and single crystal structure analysis to contain two hydrates, a dihydrate and a higher hydrate. The com position o f the latter, contradictory in the literature, could be resolved in favor o f the new one o f a heptahydrate. The dihydrate (m.p. 0.7 °C) is m onoclinic with space group P2, and Z = 2 formula units per unit cell o f dim ensions a = 6.017, b = 6.055, c = 10.377 A and ß -106.60° at -150 °C. The heptahydrate (m.p. -6 °C, dec.) is orthorhombic with space group Pnma, Z = 4, a -12.589, b = 15.251 and c = 6.645 A at -150 °C. Both hydrates contain characteristic layers o f hydrogen-bonded O atom s, which in the heptahydrate are further linked into a three-di-m ensional semi-clathrate structure.
	Reference	Z. Naturforsch. 48b, 1325—1330 (1993); eingegangen am 17. Mai 1993
	Published	1993
	Keywords	te/7-Butanol Hydrates, Melting Diagram, Crystal Structure, Hydrogen Bonding
	Similar Items	Find
	DEBUG INFO
	TEI-XML for	default:Reihe_B/48/ZNB-1993-48b-1325.pdf
	Identifier	ZNB-1993-48b-1325
	Volume	48

2	Author	Sophie Creuzet, TeresaM. Iranda, Jean-M Arc Ducruet	Requires cookie*
	Title	Comparison of Experimental and Calculated Hydrogen Bonding Properties of Some Urea and Triazine Inhibitors of Photosystem II
	Abstract	Previous studies o f structure/activity relationships o f photosystem II inhibitors, including com parisons o f their inhibitory power in herbicide-resistant and susceptible chloroplasts, have led to predict the role o f hydrogen bonding, associated to hydrophobicity, in the binding onto the Qb site. The crystallographic structures o f bacterial reaction centers now allow these bonds to be identified. In order to be able to understand the binding o f various herbicides and the effects o f resistance mutations within the Q B site, a reliable estimation o f hydrogen bonding strengths is needed. We show here, by calculating interactions with model com pounds, con trolled by physicochemical measurements, that the hydrogen bonding properties o f the C = X nucleophilic moiety present in most PS II inhibitors are different for triazines as compared to urea or amide derivatives. Semiempirical methods (AM 1) fail to reproduce the energies o f hy drogen bonds between a triazine ring nitrogen and a phenolic proton. An empirical method (SI BFA), designed to reproduce interaction energies, has been adapted with the aim o f calculat ing the binding energies o f various herbicides with models o f the Q B site.
	Reference	Z. Naturforsch. 48c, 179 (1993); received November 12 1992
	Published	1993
	Keywords	Herbicide, Herbicide Resistance, Hydrogen Bonding, M olecular Calculation, Photosystem II
	Similar Items	Find
	DEBUG INFO
	TEI-XML for	default:Reihe_C/48/ZNC-1993-48c-0179.pdf
	Identifier	ZNC-1993-48c-0179
	Volume	48

3	Author	M. Weisser, W. Weyrich	Requires cookie*
	Title	The Electronic Structure of Hydrogen Bonding in a-Oxalic Acid Dihydrate
	Abstract	Compton spectra of a-oxalic acid dihydrate single-crystal slices and powder samples were mea-sured in a helium atmosphere using 59.537 keV 241 Am radiation. In the anisotropic case, the scattering vector was oriented parallel to the shortest hydrogen bond, in the direction of the C = O bond, parallel to the C — O bond and perpendicular to the (a, c)-plane. The comparison of theoretical reciprocal form factors, calculated with a local density-approximation (LDA) method for an a-(COOH) 2 • 2H 2 0 cluster in triple-zeta basis-set quality, with the experimental data has demon-strated that there is a considerable influence of intermolecular interactions on the electronic struc-ture. Further calculations including the intermolecular interactions of the first coordination sphere by symmetrical orthogonalisation of the LDA wave functions clearly improved the agreement of experiment and theory. A theoretical analysis of the reciprocal form factor B a (s) in the direction of the three different hydrogen bonds of a-oxalic acid dihydrate on the basis of the cluster calculations has shown that in the region above s = 1.9 Ä all these bonds are dominated by electrostatic attrac-tion and exchange repulsion of the donor and the acceptor system.
	Reference	Z. Naturforsch. 48a, 315—324 (1993); received January 28 1993
	Published	1993
	Keywords	a-Oxalic acid dihydrate, Compton spectroscopy, Hydrogen bonding, Reciprocal form factor, Density functional calculations
	Similar Items	Find
	DEBUG INFO
	TEI-XML for	default:Reihe_A/48/ZNA-1993-48a-0315.pdf
	Identifier	ZNA-1993-48a-0315
	Volume	48

4	Author	Tetramethylammoniumfluorid Bildung, Wasserstoffbrückenbindung Struktur, Dieter Stäben, Dietrich Mootz	Requires cookie*
	Title	Die kristallinen Hydrate
	Abstract	The melting diagram of the system M e4N F -H 20 in the region 50-100 mol% H zO has been investigated for the first time, using D T A , D SC and tem perature-dependent X-ray powder diffraction. Four crystalline hydrates M e4N F\*H 20 were found, with x = 1 ,2 .3 3 ,4 and 5, which decom pose irreversibly above ca. 160 °C and m elt incongruently at 36 °C, congruently at 46 °C and again incongruently at 10 °C, respectively. The crystal structure o f each hydrate, except the already known one of the tetrahydrate, has b een determ ined with M oK a diffractom eter data. The monohydrate is rhombohedral with space group R3m and Z = 6 formula units per unit cell (hexagonal axes), the 2.33-hydrate m onoclinic with P2j/n and Z = 12, and the pen-tahydrate tetragonal with 142 m and Z = 2. The hydrogen-bonded H 20/F ~ structure is an iso lated centrosymmetric [F2(H 20) 2]2_ four-m em bered ring in the m onohydrate, a rather open three-dim ensional network in the 2.33-hydrate and a corrugated dense layer o f fused five-mem bered rings in the pentahydrate.
	Reference	Z. Naturforsch. 48b, 1057—57 (1993); eingegangen am 5. April 1993
	Published	1993
	Keywords	Tetramethylamm onium Fluoride, Fluoride Hydrates, M elting Diagram, Crystal Structure, Hydrogen Bonding
	Similar Items	Find
	DEBUG INFO
	TEI-XML for	default:Reihe_B/48/ZNB-1993-48b-1057.pdf
	Identifier	ZNB-1993-48b-1057
	Volume	48