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191.
The molar heat capacity of the azeotropic mixture composed of ethanol and toluene was measured by a high precision adiabatic calorimeter from 80 to 320 K. The glass transition and phase transitions of the azeotropic mixture were determined based on the heat capacity measurements. A glass transition at 103.350 K was found. A solid-solid phase transition at 127.282 K, two solid-liquid phase transitions at 153.612 and 160.584 K were observed, which correspond to the transition of metastable crystal to stable crystal of ethanol and the melting of ethanol and toluene, respectively. The thermodynamic functions and the excess ones of the mixture relative to the standard temperature 298.15 K were derived based on the relationships of the thermodynamic functions and the function of the measured heat capacity with respect to temperature. 相似文献
192.
A previous method for the determination of penicillins by direct titration with potassium iodate under strongly acidic conditions has been extended to the assay of some selected cephalosporins. Results are presented, including error and precision analyses, for the determination of cephaloridine, cephalothin and cephalexin. The appropriate stoichiometries are 1 mol cephalosporin to 3 mol iodate for cephalothin and cephaloridine; 1 mol to 2 mol iodate for cephalexin. An irreversible aqueous end-point technique has been compared with the chloroform layer method; the latter gives more precise results for the determination of cephaloridine and cephalothin (0.8% and 1.3% r.s.d. respectively). Comparable precision was obtained by either technique for the determination of cephalexin (1.39% r.s.d.). 相似文献
193.
L. C. Du S. C. Tiong Q. Zhu Allan S. Hay 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3579-3591
Zinc glutarates were synthesized from zinc oxides with varying purities via different stirring routes. The particle size and structure of these zinc glutarates were determined by wide‐angle X‐ray diffraction, transmission electron microscopy, and the laser particle size analyzer technique. The results demonstrated that the crystallinity and crystalline perfectness of zinc glutarate are the crucial factors that affect the catalytic activity for the copolymerization of carbon dioxide (CO2) and propylene oxide (PO). Additionally, the catalyst with a small particle size dramatically increased the yield of the copolymerization between CO2 and PO. High‐molecular‐weight and regular molecular structure poly(propylene carbonate)s (PPC)s were obtained from CO2 and PO with the synthesized zinc glutarates. Very high catalytic activity of 160.4 g polymer/g catalyst was afforded. The NMR technique revealed that the PPC copolymer exhibits an exact alternating copolymer structure. The relationships between the crystallinity and the particle size of catalyst with the catalytic activity are correlated and discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3579–3591, 2002 相似文献
194.
195.
在260~380 K范围内, 用DSC法研究液晶HpBAB的相变。实验查明HpBAB在室温还以玻璃性晶体状态存在。它的玻璃转变、熔化和清亮过程的热力学参数准确地被测到。提出对-正烷氧基亚苄基-对-氨基苯腈同系列中熔化熵和烷基碳原子数的线性关系; 改进Aranow统计模型并估算直线斜率为Rln(3/g)(1相似文献
196.
Zhuang Guisun Wang Yinson Tan Mingguang Zhi Min Wang Yongjie Zhang Fulin 《Journal of Radioanalytical and Nuclear Chemistry》1991,151(2):327-335
Elemental profiles of brain tumor tissues from 15 patients of astrocytomas (grade I–III) and normal human brain tissues of 23 male age matched autopsies as controls have been studied by instrumental neutron activation analysis. The SLOWPOKE reactor with a thermal neutron flux of 8·1011n·cm–2·s–1 and swimming pool type reactor with a thermal neutron flux of 1·1013n·cm–2·s–1 were used for short and long irradiation of samples, respectively. Spectrophotometry was only used for analyzing phosphorus. A total of 18 elements Se, Na, K, Br, Cl, Mn, Mg, S, Ca, Cu, Hg, Cr, Fe, Rb, Zn, Co, Sc and P has been determined for this purpose. The reliability of methods has been checked by analyzing biological standard reference materials horse kidney (IAEA H-8) and bovine liver (NBS SRM 1577a). The analytical results showed that compared with the normal brain tissues, concentrations of Ca, Fe, Cu, Zn, Se, Mn, Br and Sc were significantly higher in tumor tissues (P<0.01) and concentrations of Rb, K and P were lower, while no differences for contents of Mg, S, Cr, Hg, Na and Cl were observed. A negative correlation between P and Ca in malignant and normal brain tissues was observed. 相似文献
197.
An analytical method for analysing acrylamide in coffee was validated. The analysis of prepared coffee includes a comprehensive clean-up using multimode solid-phase extraction (SPE) by automatic SPE equipment and detection by liquid chromatography tandem mass spectrometry using electrospray in the positive mode. The recoveries of acrylamide in ready-to-drink coffee spiked with 5 and 10 μg l−1 were 96±14% and 100±8%, respectively. Within laboratory reproducibility for the same spiking levels were 14% and 9%, respectively. Coffee samples (n = 25) prepared twice by coffee machines and twice by a French Press Cafetière coffee maker contained 8±3 μg l−1 and 9±3 μg l−1 acrylamide. Five ready-to-drink instant coffee prepared twice contained 8±2 μg l−1. Hence, the results do not show significant differences in the acrylamide contents in ready-to-drink coffee prepared by coffee machine, French Press or from instant coffee. Medium roasted coffee contained more acrylamide (10 μg l−1) than dark roasted coffee (5 μg l−1). Males aged 35–45 years, drinking on average 1.1 l coffee per day are exposed to the highest doses of acrylamide from coffee. The dietary intake of acrylamide from coffee comprises, on an average, 10 μg day−1 for males and 9 μg day−1 for females aged 35–45 years. Probabilistic modelling of the exposure of Danish consumers (all adults) to acrylamide from coffee shows a mean exposure of 6.5 μg day−1 and a 95 percentile of 18 μg day−1. 相似文献
198.
Two new C18-norditerpenoid alkaloids from Aconitum delavayi 总被引:2,自引:0,他引:2
Shan Hao Jiang Hai Qing Wang Yi Ming Li Shuang Jun Lin Jun Jie Tan Da Yuan Zhu 《中国化学快报》2007,18(4):409-411
Further phytochemical investigation of the unique C18-norditerpenoid alkaloids from the roots of Aconitum delavayi Franch ledto the isolation of two new norditerpenoid alkaloids,delavaconitine F 1 and delavaconitine G 2.Their structures were determinedfrom spectroscopic evidence. 相似文献
199.
Wang X Zhang J Song A Lebrilla CB Lam KS 《Journal of the American Chemical Society》2004,126(18):5740-5749
In the "one-bead one-compound" (OBOC) combinatorial library method, each compound bead displays only one compound entity. Hundreds of thousands to millions of compound beads can be synthesized rapidly and screened simultaneously. Positive compound beads are then isolated for structural analysis. To fully exploit the power of OBOC combinatorial small molecule libraries, a robust and high throughput encoding method is needed to decode the positive compound beads. In this paper, we report on the development of a novel encoding strategy that combines the concepts of ladder-synthesis and chemical encoding on bilayer beads. In these encoded libraries, small molecule compounds are displayed on the bead surface, and cleavable coding tags consisting of a series of truncated molecules reside in the bead interior. Such a library can be easily constructed using the biphasic approach (J. Am. Chem. Soc.2002, 124, 7678) to topologically segregate the functionalities of the beads during library synthesis. The ladder members and coding tags are then released for MALDI-TOF-MS analysis. To simplify the interpretation of the mass spectra, we purposely add bromine into the cleavable linker so that the cleavage products generate a characteristic isotope fingerprint. The chemical structure of library compounds can be determined by analyzing the mass differences between adjacent peaks on the mass spectra. This encoding strategy also provides valuable information on the quality of the testing compound on the surface of the bead. To validate this methodology, a model OBOC small molecule library with 12,288 members was synthesized on TentaGel beads and screened against streptavidin. The chemical structures of the compound on each positive bead were unambiguously identified. 相似文献
200.
Tongbu Lu Xin Wang Minyu Tan Yu Liu Yoshihisa Inoue Tadao Hakushi 《Helvetica chimica acta》1993,76(1):241-247
The lanthanide nitrate complexes with 13-crown-4(13-C-4) have been prepared in AcOEt. These new complexes with the general formula Ln(NO3)3.(13-c-4) (Ln = La–Nd, Sm–Lu) have been characterized by means of elemental analysis, IR and 1H-NMR spectra, conductivity measurements, and TG-DTA techniques. The crystal and molecular structure of Nd(No3)3. (13-c-4) has been determined by single crystal X-ray diffraction. It crystallizes in the monoclinic space group P21/a with Z = 8. Lattice parameters are a = 15.393(1), b = 12.578(1), c = 19.279(2) Å, β = 113.05(1)°, V = 3435 Å3, Dc = 2.01 g cm?3, μ = 31.0 cm?1 (Mok2), F(000) = 2056. The structure was solved by Patterson and Fourier techniques and refined by least-squares to a final conventional R value of 0.032 for 5218 independent reflections with I ? 3σ(I). There are two independent Nd(No3)3 · (13-C-4) monomers in one asymmetrical unit. The coordination numbers are ten in these two independent monomers. 相似文献