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71.
Olga Franco Ingo Orgzall Günter Reck Sabine Stockhause Burkhard Schulz 《Journal of Physics and Chemistry of Solids》2005,66(6):994-1003
The crystalline structures of two modifications of a compound containing the oxadiazole ring, 2,5-di-(4-aminophenyl)-1,3,4-oxadiazole (DAPO) were determined. One of these modifications contains water molecules in the crystal structure, which is observed for the first time for an oxadiazole crystal. Both crystals show an orthorhombic structure. The water free modification, DAPO I, belongs to the space group Pbca (61) and has the lattice parameters: a=13.461(5), b=7.937(3) and c=22.816(8) Å (CCDC 246608). The water containing pseudo-polymorph, DAPO II, has the space group Cmcm (63) and the lattice parameters: a=16.330(5), b=12.307(2) and c=6.9978(14) Å (CCDC 246609). To gain information on the inter molecular interactions within the crystals, X-ray experiments under compression at ambient temperature and under heating at vacuum conditions were performed. Neither DAPO I nor DAPO II undergo phase transitions in the ressure range up to 5 GPa, as could be concluded from X-ray and Raman experiments. X-ray and calorimetric studies indicate that DAPO II dehydrates into DAPO I under increasing temperature. Structural considerations suggest a two-stage process. The compression behavior of both substances is well described by the Murnaghan equation of state (MEOS) and the values of the bulk modulus and its pressure derivative are determined for these crystals. Additionally, in the case of DAPO I, also the thermal expansion coefficient α0 was measured. 相似文献
72.
Baptiste Jaquet Dan Wei Bernd Reck Frank Reinhold Xinya Zhang Hua Wu Massimo Morbidelli 《Colloid and polymer science》2013,291(7):1659-1667
Polyelectrolyte brushes are widely used for surface modification of nano-and colloidal particles because of their ability to dramatically change their conformation, hydrophobicity, polarity, charge, etc., as a response to smooth variations in environmental conditions. In this work, we have studied experimentally the stability behavior of polymer colloids with grafted poly-acrylic acid (PAA) surface brushes. We have measured the Fuchs stability ratio (W) as a function of electrolyte concentrations at different pH. It is observed that at pH?<?3, the W values with 1 % and 2 % PAA brushes do not differ significantly from those without PAA, indicating that in their protonated state, the carboxylic groups do not contribute significantly to the colloidal stability. At the intermediate pH?~?5, the PAA brushes are partially deprotonated, and their contribution to the colloidal stability is substantial and increases as the length of the PAA brushes increases. Under alkaline conditions (pH?>?8), since most of the carboxylic groups are ionized, the colloidal stability is much higher than that at pH?~?5. However, the W values are basically the same with 1 % and 2 % PAA, implying that the contribution of the ionized AA in the two cases is practically the same. This experimental evidence indicates that only the ionized AA groups in the outer region of long brushes contribute to colloidal stability, thus supporting the hypothesis of local electroneutrality in the inner region of long brushes (LEA). 相似文献
73.
Klein JM Saggiomo V Reck L McPartlin M Pantoş GD Lüning U Sanders JK 《Chemical communications (Cambridge, England)》2011,47(12):3371-3373
A new [2+2] tetra-hydrazone macrocyclic receptor was significantly amplified in a dynamic combinatorial library upon templation with alkaline earth metal ions. After optimisation the product could be isolated in 95% yield and its interaction with ions was investigated by NMR and UV-Vis spectroscopy. 相似文献
74.
Abstract Two differently substituted crystalline 2,5-diphenyl-1,3,4-oxadiazole compounds are investigated in the pressure range up to 5GPa. Phase transitions are detected using Raman and X-ray investigations. 相似文献
75.
Burkhard Schulz Julia Bricks Yan‐Qin Li Ute Resch‐Genger Günter Reck 《Acta Crystallographica. Section C, Structural Chemistry》2004,60(6):o402-o404
1‐Methyl‐2‐[4‐phenyl‐6‐(pyridinium‐2‐yl)pyridin‐2‐yl]pyridinium diperchlorate, C22H19N32+·2ClO4−, (I), and 2‐[4‐(methoxyphenyl)‐2,2′‐bipyridin‐6‐yl]‐1‐methylpyridinium iodide, C23H20N3O+·I−, (II), both crystallize in the monoclinic space group P21/c. In contrast with the monocharged molecule of (II), the doubly charged molecule of (I) contains an additional protonated pyridine ring. One of the two perchlorate counter‐anions of (I) interacts with the cation of (I) via an N—H⋯O hydrogen bond. In (II), two molecules related by a centre of symmetry are connected by weak π–π interactions, forming dimers in the crystal structure. 相似文献
76.
F. Emmerling G. Reck W. Kraus I. Orgzall B. Schulz 《Crystal Research and Technology》2008,43(1):99-107
The crystal structures of the 1,3,4 oxadiazole compounds N,N‐dimethyl‐N‐[4‐(1,3,4‐oxadiazol‐2‐yl)phenyl]amine ( 1 ) and 2‐methyl‐5‐phenyl‐1,3,4‐oxadiazole ( 2 ) have been determined. In case of 1 no adequate crystals were available; therefore the structure was solved at room temperature from X‐ray powder diffraction data using the method of simulated annealing. This solution is compared to a second one obtained by applying the molecular replacement method. Subsequent Rietveld refinements combined with the so called two stage method based on the data collected to 1.6 Å resolution yielded an Rwp value of 7.27% for 1 . Compound 1 crystallizes in the orthorhombic space group P212121 with lattice parameters of a = 7.599(4) Å, b = 6.004(2) Å, c = 21.736(3) Å. The crystal structure of 2 was solved by means of single crystal structure analysis (monoclinic space group P21/c, a = 8.010(3) Å, b = 10.783(4) Å, c = 19.234(7) Å, β = 90.794(9)°). (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
77.
Tiemann CO Thode AM Straley J O'Connell V Folkert K 《The Journal of the Acoustical Society of America》2006,120(4):2355-2365
A three-dimensional localization method for tracking sperm whales with as few as one sensor is demonstrated. Based on ray-trace acoustic propagation modeling, the technique exploits multipath arrival information from recorded sperm whale clicks and can account for waveguide propagation physics like interaction with range-dependent bathymetry and ray refraction. It also does not require ray identification (i.e., direct, surface reflected) while utilizing individual ray arrival information, simplifying automation efforts. The algorithm compares the arrival pattern from a sperm whale click to range-, depth-, and azimuth-dependent modeled arrival patterns in order to estimate whale location. With sufficient knowledge of azimuthally dependent bathymetry, a three-dimensional track of whale motion can be obtained using data from a single hydrophone. Tracking is demonstrated using data from acoustic recorders attached to fishing anchor lines off southeast Alaska as part of efforts to study sperm whale depredation of fishing operations. Several tracks of whale activity using real data from one or two hydrophones have been created, and three are provided to demonstrate the method, including one simultaneous visual and acoustic localization of a sperm whale actively clicking while surfaced. The tracks also suggest that whales' foraging is shallower in the presence of a longline haul than without. 相似文献
78.
Crossed beams of energetic cesium atoms (25–350 eV) and thermal Cf3X (X = Cl, Br and I) produce X? and F? as the major anions. The intensity ratio (F?/X?) is measured as a function of energy. A hard-sphere stripping model is in reasonable accord with the data. 相似文献
79.
Thode A Straley J Tiemann CO Folkert K O'Connell V 《The Journal of the Acoustical Society of America》2007,122(2):1265-1277
Sperm whales (Physeter macrocephalus) have learned to remove fish from demersal longline gear deployments off the eastern Gulf of Alaska, and are often observed to arrive at a site after a haul begins, suggesting a response to potential acoustic cues like fishing-gear strum, hydraulic winch tones, and propeller cavitation. Passive acoustic recorders attached to anchorlines have permitted continuous monitoring of the ambient noise environment before and during fishing hauls. Timing and tracking analyses of sperm whale acoustic activity during three encounters indicate that cavitation arising from changes in ship propeller speeds is associated with interruptions in nearby sperm whale dive cycles and changes in acoustically derived positions. This conclusion has been tested by cycling a vessel engine and noting the arrival of whales by the vessel, even when the vessel is not next to fishing gear. No evidence of response from activation of ship hydraulics or fishing gear strum has been found to date. 相似文献
80.
The work has highlighted the importance of choosing the correct pigment for paratoluene sulphonic acid (PTSA) catalysed paints. Generally, surface treated TiO2 grades which are basic in nature resulted in the best optical performance in comparison to acidic surface treated grades. The relative performance of the acidic surface treated grade can be improved by increasing the PTSA level in the paint or by using a resin with a higher acidity level. It is postulated that for these TiO2 grades, the higher acid levels were found to give better steric repulsion. However, overall, the basic surface treated grade retained the best optical performance in PTSA catalysed paint systems. 相似文献