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991.
992.
The liquid chromatographic enantiomer separation of N-fluorenylmethoxycarbonyl (FMOC) protected alpha-amino acids and their ethyl ester derivatives was performed on polysaccharide-derived chiral stationary phases, Chiralcel OD, Chiralpak AD, and Chiralpak AS. In general, Chiralcel OD and Chiralpak AD showed good performance for resolution of N-FMOC alpha-amino acids and their ethyl esters, respectively. All investigated N-FMOC alpha-amino acid enantiomers were baseline separated on Chiralcel OD or Chiralpak AD, whereas N-FMOC alpha-amino acid ethyl ester enantiomers were baseline resolved (alpha = 1.15-3.03) on Chiralpak AD, except for two analytes. The L-enantiomers of all examined FMOC alpha-amino acid ethyl ester derivatives are preferentially retained on Chiralpak AD, while the elution orders of the other enantiomer separations are not consistent. 相似文献
993.
994.
Koichi Tanaka Hideyuki Takano Zofia Urbanczyk-lipkowska 《Journal of inclusion phenomena and macrocyclic chemistry》2006,56(3-4):281-285
The host compounds 1,1’-binaphthyl-2,2′-dihydroxy-5,5′-dicarboxylic acid (1) and 1,1′-binaphthyl-2,2′-dihydroxy-6,6′-dicarboxylic acid (2) have been synthesized, and their inclusion properties have been studied. Inclusion complexes formed by 1 and 2 with volatile guests such as acetone and methanol release the guests only at much higher temperatures than their boiling
points. The crystal structures of the inclusion complexes have been determined from single crystal X-ray diffraction data
and show different host lattices. 相似文献
995.
Łada T. Przybylski K. Morawski A. Prażuch J. Brylewski T. 《Journal of Thermal Analysis and Calorimetry》2001,64(2):611-615
The fabrication method of superconducting thin films of compositions HgBa2Ca2Cu3O8+δ (Hg-1223) and Tl2Ba2CuOy (2201) on single-crystalline SrTiO3 and LaAlO3 substrates is reported. The highest obtained T
c was 134 K and J
c over 106 A cm–2 at 77 K. High pressure DTA(HP-DTA) was applied to grow mercury- and thallium-based high-temperature superconducting crystals
and thin films, to identify melting points of particular phases within these oxide systems and determine suitable processing
conditions. The DTA system operates at the: maximum temperature of 1200°C, volume up to 5 cm3, working pressure up to 1.5 GPa and at a working atmosphere — inert gas with up to 25% oxygen.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
996.
据不同地貌、地质条件在30个县市按剖面、同步、随机取土壤样品372份.测定硒等微量元素含量.作等级相关分析显示。土壤硒含量与消化系统癌呈负相关关系.作相对危险度、剂量-效应及多因素分析,认为此负相关关系并非偶然现象. 相似文献
997.
Hamada Fumio Kondo Yoshihiko Ito Riko Suzuki Iwao Osa Tetsuo Ueno Akihiko 《Journal of inclusion phenomena and macrocyclic chemistry》1993,16(3):273-281
The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C12H17N4OS+·I– · 1.5 H2O, monoclinic,P21/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) Å3,Z=8,D
c=1.606 g cm–3,R=0.045 for 3328 observed reflections.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages). 相似文献
998.
999.
The mass-transter characteristics of a two-phase system formed by mixing a fixed quantity (20 v/v%) of organic solvent with an aqueous ferricyanide electrolyte solution in an RDE system were studied. The Levich eqution, I1 = 0.62 nFACbD2/3v?1/6ω1/2, was found to be applicable to the two-phase system with only a minor modification in the angular velocity (ω) at Reynolds numbers between 3–5 × 104. The experimental results indicate that the interfacial tension is the most important variable for the two-phase system. One group of organic solvents with smaller interfacial tension, such as benzene or toluene, needs a modification of the Levich equation by replacing the observed angular velocity (ωo) with the true angular velocity (ωt) which was observed to be 1.1 times the observed angular velocity. For the other group with larger interfacial tension, such as n-hexane or cyclohexane, there is no need to modify the observed angular velocity. In other words, the Levich equation may be expressed as I1 = 0.65 nFACbD2/3v?1/6ω1/2 for two-phase solution if the interfacial tension is smaller than 37.0 dyne/cm. 相似文献
1000.
Haoshuang Gu Yongming Hu Hao Wang Xiangrong Yang Zhenglong Hu Ying Yuan Jin You 《Journal of Sol-Gel Science and Technology》2007,42(3):293-297
Single crystalline nanowires of lead titanate (PbTiO3) were fabricated by hydrothermal method at 200°C using lead acetate and n-tetrabutyl titanate as starting materials, where sodium hydroxide was served as a mineralizer. Crystalline phases, microstructure
and optical properties of PbTiO3 nanowires were investigated. The PbTiO3 nanowires were uniform and continuous along the long axis, and were composed of single crystalline PbTiO3 with a tetragonal perovskite structure. The diameter of a single nanowire was around 12 nm and the length reached up to 3 μm.
The chemical composition of the samples and the valence states of elements were determined by X-ray photoelectron spectroscopy
(XPS). The ultraviolet/visible absorption spectroscopic investigation suggested that the absorption edge of optical transition
of the first excitonic state occurred at around 320 nm. A blue-green light emission peaking at about 471 nm (2.63 eV) is observed
at room temperature, and the intensity of this emission increased with increasing excitation wavelength. Oxygen vacancies
are responsible for the light emission of PbTiO3 nanowires. 相似文献