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111.
Ligia R. Gomes R. Alan Howie John Nicolson Low Ana S. M. C. Rodrigues Luís M. N. B. F. Santos 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):o492-o497
A low‐temperature polymorph of 1,1′:3′,1′′:3′′,1′′′:3′′′,1′′′′‐quinquephenyl (m‐quinquephenyl), C30H22, crystallizes in the space group P21/c with two molecules in the asymmetric unit. The crystal is a three‐component nonmerohedral twin. A previously reported room‐temperature polymorph [Rabideau, Sygula, Dhar & Fronczek (1993). Chem. Commun. pp. 1795–1797] also crystallizes with two molecules in the asymmetric unit in the space group P. The unit‐cell volume for the low‐temperature polymorph is 4120.5 (4) Å3, almost twice that of the room‐temperature polymorph which is 2102.3 (6) Å3. The molecules in both structures adopt a U‐shaped conformation with similar geometric parameters. The structural packing is similar in both compounds, with the molecules lying in layers which stack perpendicular to the longest unit‐cell axis. The molecules pack alternately in the layers and in the stacked columns. In both polymorphs, the only interactions between the molecules which can stabilize the packing are very weak C—H...π interactions. 相似文献
112.
This work describes the attachment of two amino acid derivatives by olefin cross-metathesis using Grubbs' second generation catalyst. They were connected at the carboxyl termini. In addition, a cyclic dilactam scaffold was used, which reacted with only a fraction of the amino acid derivatives. The remaining fraction coupled directly coupled with no scaffold. This highly trans-selective double attachment resulted in the cross-metathesis of a variety of amino acids in a single reaction. 相似文献
113.
John Nicolson Low Celeste Garcia Manuel Melguizo Justo Cobo Adolfo Snchez Manuel Nogueras M. D. Lpez 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(11):e526-e527
The title compound, C25H29N3O13S, has peripheral acetyl and carbomethoxy groups which show disorder. The absolute structure, although known from the starting materials, was confirmed by the analysis. There are no intermolecular hydrogen bonds. This structure is of importance because it elucidates the pathway for hetero‐Diels–Alder reactions between dimethyl acetylenedicarboxylate and 6‐aminopyridin‐4(3H)‐one derivatives catalyzed by trifluoroacetic acid. 相似文献
114.
Rafael Cuesta Paloma Arranz‐Mascars John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(8):918-921
In the title compound, [Na(C5H5N4O3)]·2H2O, each Na cation is linked to three C5H4N4O3? anions and two water molecules, forming approximately octahedral NaNO5 units; the cations and the anions form molecular ladders, and each ladder is linked to four neighbouring ladders by O—H?O and O—H?N hydrogen bonds. 相似文献
115.
Celeste Garcia Antonio Quesada Manuel Melguizo Justo Cobo Manuel Nogueras Adolfo Snchez Debbie Cannon John Nicolson Low 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(9):1103-1105
The title compound, C9H12N2O3, crystallizes with two molecules in the asymmetric unit. There is extensive hydrogen bonding which results in the formation of a two‐dimensional corrugated sheet. This supramolecular structure is determined by the formation of hydrogen‐bonded chains resulting from the presence of a 6‐amino group and an ethoxycarbonyl group as substituents on a pyridine ring in relative para positions which constitute a π‐electron `push–pull' system. 相似文献
116.
The temporal pulse train modulation during laser percussion drilling was found to effect significant changes to the material ejection processes. In particular, distinct differences in the material ejection processes have been observed between a temporal pulse train shaping technique termed as sequential pulse delivery pattern control (SPDPC) and the normal delivery pattern (NDP), wherein the parameters of successive laser pulses were constant. Due to the reduced upward material removal fractions in SPDPC drilling, the spatter deposition area was reduced from approximately 6.7 to 2.7 mm2. In addition, the melt layer thicknesses at the hole bottom were significantly increased from 11–61 to 18–369 μm. Such changes were identified as being due to the low laser pulse intensities before beam breakthrough associated with the SPDPC method. It was observed that the use of the linearly increasing SPDPC method increased the downward material removal fractions, from 20% to 28% observed in NDP drilling, to 34%–39%. Such an increase in the downward material ejection mechanism in SPDPC drilling was identified as being primarily due to the pointed blind-hole profile generated before the onset of beam breakthrough. The work has shown that modulating the entire pulse train in laser percussion drilling could control the material ejection processes. Furthermore, the fundamental elements of the SPDPC technique are given in terms of the rate of energy deposition and total pulse train energy. 相似文献
117.
We present exact analytic solutions describing the equilibrium states available to a one-dimensional, self-gravitating cloud of gas subject to an external constant gravitational acceleration due to a plane of “stars”. The gas is taken to be heated at a rate proportional to the local gas density and is cooling by both radiation and conduction. The solutions are valid for a thermal conductivity which is an arbitrary function of gas temperature, T, and for radiative cooling which is proportional to the local gas density, ?, multiplied by an arbitrary function of gas pressure, ?. Illustrations of the general spatial dependence are given for the cases where the radiative cooling is proportional to ?2T, and in which the thermal conductivity is either constant, or proportional to Ta(a > 0) in the limits of T tending zero or infinity, respectively.We show that the phenomenon of density “inversion”, reported earlier, is indeed ameliorated by the radiative cooling term, as we had speculated it might be, but is not removed. This indicates that the phenomenon of density inversion is of rugged quality, persisting under a wide variety of conditions and, therefore, of general astrophysical import. We also show that, depending on the ratios of various parameters entering the problem, there is a new phenomenon possible in which the gas temperature has a local minimum at some non-central location so that a wedge of cool gas is in equilibrium surrounded by a hot medium.We have done these calculations as an aid to understanding the complicated behavior of interstellar gas clouds in particular, and the general physical interplay between force balance and energy balance in models of gas clouds more realistic than those heretofore available. 相似文献
118.
An HPLC assay for the determination of ketoconazole in common pharmaceutical preparations 总被引:3,自引:0,他引:3
An HPLC method is described using octadecylsilica (3 microns) with an acetonitrile phosphate buffer mobile phase containing diethylamine which is capable of separating ketoconazole [(+/-)-cis-1-acetyl-4-(4[2-(dichlorophenyl)-2- (1H-imidazol-1-ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl)pi perazine] from four related compounds, (R049223, R063600, R053165 and R039519) and from excipients in tablets, cream and shampoo. The method was validated using an external calibration method for tablets, shampoo and creams and a standard addition method for cream. The limits of detection for the related compounds in the presence of ketoconazole are also reported. 相似文献
119.
Simon J. Garden Marilza B. Corrêa Angelo C. Pinto James L. Wardell John N. Low Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(4):o234-o238
In ethyl N‐[2‐(hydroxyacetyl)phenyl]carbamate, C11H13NO4, all of the non‐H atoms lie on a mirror plane in the space group Pnma; the molecules are linked into simple chains by a single C—H⋯O hydrogen bond. The molecules of ethyl N‐[2‐(hydroxyacetyl)‐4‐iodophenyl]carbamate, C11H12INO4, are linked into sheets by a combination of O—H⋯I and C—H⋯O hydrogen bonds and a dipolar I⋯O contact. Ethyl N‐[2‐(hydroxyacetyl)‐4‐methylphenyl]carbamate, C12H15NO4, crystallizes with Z′ = 2 in the space group P; pairs of molecules are weakly linked by an O—H⋯O hydrogen bond and these aggregates are linked into chains by two independent aromatic π–π stacking interactions. 相似文献
120.
Yuen MY Kui SC Low KH Kwok CC Chui SS Ma CW Zhu N Che CM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(47):14131-14141
A series of platinum(II) complexes bearing tridentate cyclometalated C^N^N (C^N^N=6-phenyl-2,2'-bipyridine and π-extended R-C^N^N=3-[6'-(naphthalen-2'-yl)pyridin-2'-yl]isoquinoline) ligands with fluorene units have been synthesised and their photophysical properties have been studied. The fluorene units are incorporated into the cyclometalated ligands by a Suzuki coupling reaction. An increase in the π-conjugation of the cyclometalated ligands confers favourable photophysical properties compared to the 6-phenyl-2,2'-bipyridine analogues. The fluorene-based platinum(II) complexes display vibronic-structured emission bands with λ(max)=558-601 nm, and high emission quantum yields up to 0.76 in degassed dichloromethane. Their emissions are tentatively assigned to excited states with mixed (3)IL/(3)MLCT parentage (IL=intraligand, MLCT=metal-to-ligand charge transfer). The crystal structures of these platinum(II) complexes reveal extensive Pt(II)···π and/or π-π interactions. The fluorene-based platinum(II) complexes are soluble in organic solvents, have high thermal stability with decomposition temperature >350 °C, and can be thermally vacuum-sublimed or solution-processed as phosphorescent dopants for the fabrication of organic light-emitting diodes (OLEDs). A monochromic OLED with 3d as dopant (2 wt%) fabricated by vacuum deposition gave a current efficiency of 14.7 cd A(-1) and maximum brightness of 27000 cd m(-2). A high current efficiency (9.2 cd A(-1)) has been achieved in a solution-processed OLED using complex 3f (5 wt%) doped in a PVK (poly(9-vinylcarbazole)) host. 相似文献