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151.
Israel Goldberg Zafra Stein Koichi Tanaka Fumio Toda 《Journal of inclusion phenomena and macrocyclic chemistry》1991,10(1):97-107
The crystal structures of the 2,2-di(p-hydroxyphenyl)propane host and its 1:1 adducts withm-andp-cresol guests have been studied. The preferential complexation of this host withp-cresol overm-cresol is related to the opposite trend exhibited by 1,1-di(p-hydroxyphenyl)cyclohexane; both hosts can separate effectively the two cresols from their liquid mixture by crystalline inclusion. A plausible explanation of the different inclusion features is provided by examining the intermolecular association in the corresponding solids. The analysed structures are stabilized by strong and continuous H-bonding between the constituent entities along two dimensions, and by weak van der Waals forces along the third axis. The p-cresol complex of the title host reveals a unique arrangement within and a more efficient packing of the layered structure, and thus represents a more stable and less soluble crystal lattice than itsm-cresol analog.Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82099 (8 pages). 相似文献
152.
Rafael Jimnez Elena Bueno Israel Cano Elizabeth Corbacho M. Eugenia Fernndez Lidia Gmez Jesús Graciani María Hernndez M. Teresa Matitos Jos Ortíz Pilar Lpez‐Cornejo Rafael Prado‐Gotor 《国际化学动力学杂志》2004,36(12):627-633
The kinetics of substitution of H2O by Ru(NH3)5pz2+ (pz = pyrazine) in Fe(CN)5H2O3? have been studied in micellar aqueous solutions of sodium dodecylsulfate (SDS). Experimental results are discussed by using an approach based on the transition‐state theory. This approach is better than others based on the pseudophase model, which can also be used, because it is able to give a clear meaning to the parameters of the model. Trends in the observed reactivity are explained by a change in the degree of association of one of the reactants to the micelles (Ru(NH3)5pz2+ in the present work). This association is governed by an equilibrium constant that depends on the electrostatic potential at the surface of the micelles. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 627–633, 2004 相似文献
153.
154.
155.
R. Krishna Kumar Israel Goldberg 《Angewandte Chemie (International ed. in English)》1998,37(21):3027-3030
Channels make up 46% of the crystal volume: A two-dimensional coordination polymer of exceptional structural regularity (see schematic drawing; tpp=tetraphenylporphyrin, tpyp=tetrapyridylporphyrin) was assembled from [MnIII(tpp)]⋅ClO4 and tpyp. The crystal packing of these polymers yields an open bulk structure with networks of perpendicular channels filled with nitrobenzene solvent molecules. Only oligomeric entities are formed by the reaction of [ZnII(tpp)] with tpyp. 相似文献
156.
IS Ibarra JA Rodriguez ME Páez-Hernández EM Santos JM Miranda 《Electrophoresis》2012,33(13):2041-2048
A magnetic solid-phase extraction (MSPE) method combined with capillary electrophoresis for the simultaneous determination of seven quinolones (QNs) (danofloxacin, ciprofloxacin, marbofloxacin, enrofloxacin, difloxacin, oxolinic acid, and flumequine), using (S)-(+)-6-methoxy-α-methyl-2-naphthaleneacetic acid as internal standard, in milk samples was developed. The variables involved in the preconcentration magnetic procedure were: the composition of the magnetic support composition, the sample pH, and the weight of magnetic adsorbent used. The variables were optimized using a simplex-lattice design. Different magnetite covered with octyl-phenyl silica adsorbents were synthesized by varying the molar ratio of phenyltrimethylsilane and octyltrimethoxysilane; the solids were evaluated for QN preconcentration. Under optimal conditions, a linear range was obtained from 27 to 1000 μg L(-1) with limits of detection ranging from 9 to 12 μg L(-1) for the seven QNs. The absolute recoveries of the seven QNs at three different spiked levels (40, 150, and 400 μg L(-1) ) ranged from 74% to 98% with a relative standard deviation less than 10% in all cases. The proposed method was applied to analyze 20 whole milk samples of different brands. All samples were positive for the presence of QN residues; in some cases, extract dilution was required. The concentrations found are in the range from 31.1 to 5047.3 μg L(-1) . Marbofloxacin was the most frequently found. The method proposed offers advantages in terms of simplicity, sensitivity, efficiency, cost, and analysis time making it an alternative for the analysis of QNs in whole milk samples. 相似文献
157.
158.
Schottenberger H Wurst K Griesser UJ Jetti RK Laus G Herber RH Nowik I 《Journal of the American Chemical Society》2005,127(18):6795-6801
X-ray structure determinations of two different single crystals of octamethylferrocenium tetrafluoroborate (OMFc(+)BF(4)(-)) revealed conformational polymorphism with ligand twist angles of 180 degrees and 108 degrees , respectively. Their concomitant occurrence could be explained by the small lattice energy difference of 3.2 kJ mol(-1). Temperature-dependent Moessbauer spectroscopy of (57)Fe-labeled OMFc(+)BF(4)(-) over the range 90 < T < 370 K did not show the anomalous sudden increase in the motion of the metal atom as observed in neutral OMFc. Broadened absorption curves characteristic of relaxation spectra were obtained with an isomer shift of 0.466(6) mm s(-1) at 90 K. The temperature dependence of the isomer shift corresponded to an effective vibrating mass of 79 +/- 10 Da and, in conjunction with the temperature dependence of the recoil-free fraction, to a Moessbauer lattice temperature of 89 K. The spin relaxation rate could be better described by an Orbach rather than a Raman process. At 400 K, a reversible solid-solid transition to a plastic crystalline mesophase was noted. 相似文献
159.
Gershman Z Goldberg I Gross Z 《Angewandte Chemie (International ed. in English)》2007,46(23):4320-4324
160.
Israel Vainsencher 《Bulletin of the Brazilian Mathematical Society》1987,18(1):81-89
We show the component of the Hilbert scheme of twisted cubic curves is the blowup of the variety of determinantal nets along
the subvariety of nets with a fixed plane. 相似文献