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81.
Hi Taing Jacob G. Rothera Justin F. Binder Charles L. B. Macdonald 《Liquid crystals》2018,45(8):1147-1154
Conformationally flexible cores that generate large free volume when stacked and have an insufficient number of side-chains for filling the lateral space around each core have been proposed as design criteria for discotic liquid crystals that display nematic rather than columnar mesophases. Presented here are 1,3,5-triazines substituted with three thiophene carboxylate ester groups that fulfil these design criteria. Nine derivatives with linear, branched, and chiral ester chains were synthesised and their mesomorphism was studied by polarised optical microscopy, differential scanning calorimetry, and powder x-ray diffraction. Triazines with linear propyl to octyl chains display monotropic nematic discotic mesophases that crystallise within hours or days or when mechanically agitated. Packing structures for the nematic phases are proposed based on the single crystal structure of the ethyl ester. Their unusually slow nucleation and crystal growth can be attributed to the large number of possible low energy conformations that arise from the conformationally flexible core. Incorporation of racemic and chiral branched chains expectedly lowers the melting points of these derivatives but, unexpectedly, enhances nucleation and crystal growth well above the temperature ranges of their hypothetical nematic phases. Chiral nematic discotic mesophases were obtained for binary mixtures of derivatives with chiral branched and linear chains. 相似文献
82.
Cecily Eldridge Gracia Quek Michael Sako John H. Ryan Simon Saubern Mary Chebib James M. Macdonald 《Tetrahedron》2018,74(12):1245-1252
Four histrionicotoxin analogues were prepared in an efficient manner utilizing a nitrone dipolar cycloaddition reaction as the key step in forming tricyclic intermediate 13. The nitrile in intermediate 13 was reduced with DIBAL to an aldehyde which then underwent Z-selective Wittig reactions to produce intermediates containing the Z-alkene side-chain. Hydrogenation of the Z-alkenes produced saturated histrionicotoxin analogues whereas reduction with SmI2 afforded the unsaturated histrionicotoxin analogues. The histrionicotoxin analogues were shown to be potent non-competitive antagonists of the α4β2 and α7 nAChR's with the most potent analogue 3 displaying IC50's of 0.10 μM and 0.45 μM against the α4β2 and α7 nAChR's, respectively. The unsaturated analogues 15 and 18 displayed Hill slope (nH) of approximately 1 whilst the saturated analogues 16 and 3 had a nH of approximately 0.5, which may indicate that the saturated analogues are binding to more than one binding site. 相似文献
83.
H. J. Eichler R. Elschner G. Heppke R. Macdonald H. Schmid 《Applied physics. B, Lasers and optics》1995,61(1):59-62
Low-molar-mass liquid crystals consisting of a binary nematic mixture of two-naphthylester which exhibit an anisotropic glassy state at room temperature have recently proven to be a suitable material for erasable optical data-storage applications. Using the holographic-grating technique, it is shown that more than 1000 all-optical write, read and erase cycles can be realized without remarkable loss of reversibility. The recording intensities are of the order of 100 W/cm2 and optical erasure can be achieved with about twice that intensity. The times for recording and erasure of the optical gratings range on the millisecond scale and the stored gratings persist several months with a diffraction efficiency of typically 1 %. The spatial resolution has been proven down to 2 µm so far. The obtained results are compared with other reversible recording materials. 相似文献
84.
The rate constant for the reaction of the isocyanato radical, NCO(X2Pi) with chlorine atoms, Cl(2P), has been measured at 293 +/- 2 and 345 +/- 3 K to be (6.9 +/- 3.8) x 10(-11) and (4.0 +/- 2.2) x 10(-11) cm3 molecules(-1) s,(-1) respectively, where the uncertainties include both random and systematic errors. The measurements were carried out at pressures of 1.3-6.2 Torr with either Ar or CF4 as the bath gas and were independent of both pressure and nature of the third body. Equal concentrations of NCO and Cl atoms were created by 248 nm photolysis of ClNCO. The reaction was monitored by following the temporal dependence of NCO(X2Pi) using time-resolved infrared absorption spectroscopy on rotational transitions of the NCO(10(1)1) <-- (00(1)0) combination band. The reaction rate constant was determined by using a simple chemical model and minimizing the sum of the residuals between the experimental and computer generated temporal NCO concentration profiles. The reaction Cl + ClNCO --> Cl2 + NCO was found to contribute to the observed NCO. The rate constant for this reaction was found to be (2.4 +/- 1.6) x 10(-13) and (1.9 +/- 1.2) x 10(-13) cm3 molecules(-1) s,(-1) at 293 and 345 K, respectively, where the uncertainties include both random and systematic error. 相似文献
85.
Digby D. Macdonald M. E. Estep M. D. Smith J. B. Hyne 《Journal of solution chemistry》1974,3(9):713-725
The influence of N,N-dimethylformamide, N,N-dimethylacetamide, 2-pyrrolidinone, N-methyl-2-pyrrolidinone, and N-t-butyl-2-pyrrolidinone on the temperature of maximum density (TMD) of water has been investigated. Heats of solution for these compounds and for diethylsulfoxide, tetramethylene sulfoxide, tetramethylene sulfone, dimethyl sulfoxide, and tetrahydrofuran in water at 23°C are also reported. These data, together with published TMD and heat of solution data for other solutes, are used to examine the relationship between the enthalpy change on dissolution of a solute in water and the effect of the dissolved substance on the structure of water as reflected by changes in the temperature of maximum density of the system. 相似文献
86.
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88.
Laser-induced matrix-isolation site-selection fluorescence spectrometry is used to obtain narrowed-line spectra, linear dynamic ranges and limits of detection for four isomeric dibenzacridines in argon at 15 K. Site-selection fluorescence is used to determine dibenzacridines in two synthetic mixtures, a four-component mixture of the isomeric dibenzacridines and a thirteen-component polycyclic aromatic hydrocarbon mixture. The capabilities of site-selection and Shpol'skii fluorescence spectrometry for the identification and determination of aza-arenes in complex mixtures are compared. 相似文献
89.
B.H. Olaniyi G.A. Beer A. Fry J.A. Macdonald G.R. Mason A. Olin R.M. Pearce P.R. Poffenberger 《Nuclear Physics A》1982,384(3):345-352
We have measured the energies and linewidths of the pionic Kα X-rays for 20Ne and 22Ne using a natural liquid-neon target. The results are
20Ne | 22Ne | |
Neenergy (keV) | 239.12±0.14 | 230.49±0.88 |
width (keV) | 15.43±0.41 | 12.65±3.51 |