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991.
Alan P. Marchand Anna Hazlewood Zilin Huang Satish Kumar Vadlakonda John-David R. Rocha Trevor D. Power Kata Mlinarić-Majerski Lada Klaić Goran Kragol Jeffrey C. Bryan 《Structural chemistry》2003,14(3):279-288
Bis-cage-annulated 18-crown-6 and 20-crown-6 macrocyclic ethers (i.e., 1 and 2, respectively) have been synthesized, and their alkali metal picrate extraction profiles have been determined. Host system 1 proved to be a significantly more avid alkali metal cation complexant than 2 and somewhat more avid than 18-crown-6. Both 1 and 18-crown-6 display modest selectivity toward K+ and Rb+. A stable host–guest complex was prepared by slow evaporation of a CH2Cl2–hexane solution of an equimolar mixture of 2 and potassium picrate. The X-ray crystal structure of this complex reveals that picrate anion functions as a bidentate ligand therein. The gas-phase interaction energy between the 2 K+ complex and picrate anion was calculated to be ca. –64.9 kcal mol–1, thereby indicating that participation of picrate anion as an additional bidentate ligand results in significant stabilization of complex 10. 相似文献
992.
For chiral primary amino compounds not separable by cyclodextrins alone, chiral recognition was successfully achieved by the formation of a sandwiched complex of the non-chiral 18-crown-6, the chiral amine and cyclodextrin (CD) [18-crown-6+amino compound+CD]. The separation of 1-methyl-3-phenylpropylamine and 1,2,3,4-tetrahydro-1-naphthylamine racemates showed the special function of the non-chiral 18-crown-6 on chiral recognition. By formation of the sandwiched complex, the chiral center of 1-methyl-3-phenylpropylamine was successfully recognized, and resolution of 1,2,3,4-tetrahydro-1-naphthylamine dramatically increased. In these studies, the mobility differences of the enantiomers were evaluated as a function of the concentration of cyclodextrins with and without the 18-crown-6, and as a function of the concentration of the 18-crown-6. In addition, the separations by this method were compared to those by the chiral 18-crown-6 reagent. 相似文献
993.
STUDY ON PREPARATION OF INORGANIC COMPOSITE MEMBRANE AND ITS PROPERTIES FOR HYDROGEN PERMEATION
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IntroductionDevclopmcntoftcchniqucsforthcscparationofgascousmixturesisofgrcatimportancetochemicalindustries.Rccentadvanccsinceramicmaterialprocessinghavcstimulatedtheeffortstodcvclopccramicormctallicmcmbrancsforgasseparation.Suchmembraneswouldbesuitableforthescparationsathightemperatureatx`hichthcx`ellcstablishedorganicpol}mermcmbranescannotfunctionButmostcommercialceramicmembranesxvhichcanbcobtainedinmarkctaremicroporous(porediamcterfromO.ItoloPm)whereseparationmcchanismisgovcrncdbyKnudscnd… 相似文献
994.
水杨基荧光酮—过氧化氢催化动力学光度法测定痕量锇(Ⅳ) 总被引:5,自引:0,他引:5
在碱性介质中,痕量锇(Ⅳ)对水杨基荧光酮(SAF)与过氧化氢的氧化还原反应有显著的催化作用。本文以此为基础,提出用分光光度催化动力学测定痕量锇(Ⅳ)的新方法。本法未加掩蔽剂时的线性范围是0.08-0.80μg/L,加入掩蔽剂后的线性范围是0.08-0.80μg/L,检出限为0.08μg/L。本法用于实际样品中Os(Ⅳ)的测定,结果良好,本实验还测定了此催伦反应的活化能和反应级数。 相似文献
995.
微量元素锌促进儿童生长发育临床研究 总被引:1,自引:0,他引:1
报道以微量元素锌治疗缺锌患儿118例并与114例作对照观察.结果发现,衡量生长发育与营养的敏感指标:身高、体重、血清白蛋白及血色素等参数,治疗组比对照组都显著提高(P值<0.01).证明锌制剂对缺锌儿童有显著的促进生长发育及改善营养状态作用,作者并对锌的作用机理作了论述. 相似文献
996.
997.
聚碳酸酯合成工艺开发的新进展 总被引:6,自引:0,他引:6
本文从工艺开发的角度,简要评介了目前聚碳酸酯两大工业生产工艺,即光气化界面缩聚工艺和熔融酯交换缩聚工艺的研究开发新动向。 相似文献
998.
Time-of-flight mass spectrum of C_nB~- has been recorded on a selfbuilt instrument with laser vaporization of tetraphenylboron sodium. By analysis of the com-position of the anions, it is found that number of the boron atoms in any of these ions equals to the number of the charges carried by the anion, and the sum of the numbers of the carbon and boron atoms in these species are always the odd numbers. The experimental results show that boron atom has a strong tendency to attract an electron so that those C_nB~- will have similar electronic structures as C_n, and carbon clusters with odd members are always more stable than their even neighbors. 相似文献
999.
合成了金(Ⅲ)与七种中性氧配体RnXO(R=辛基或苯基;X=N,P,As和S;n=2,3)形成的十种配合物,可概括为两种类型:H(RnXO)x·AuCl_4·Sy(RnXO=TONO、TOPO、TPPO、DOSO、DPSO、TPAsO和bipyO_2;S=乙醇或水;x=1,2,3,y=0,1,2或3)和[Au(L)X_2](L=bipyO_2;X=Cl或Br)。用元素分析、摩尔电导、紫外和红外光谱、核磁共振和热重分析等方法测定了它们的组成和性质,并对其可能的结构也进行了讨论。 相似文献
1000.
Huang F Switek KA Zakharov LN Fronczek FR Slebodnick C Lam M Golen JA Bryant WS Mason PE Rheingold AL Ashraf-Khorassani M Gibson HW 《The Journal of organic chemistry》2005,70(8):3231-3241
Four new bis(m-phenylene)-32-crown-10-based cryptands with different third bridges were prepared. Their complexes with paraquat derivatives were studied by proton NMR spectroscopy, mass spectrometry, and X-ray analysis. It was found that these cryptands bind paraquat derivatives very strongly. Specifically, a diester cryptand with a pyridyl nitrogen atom located at a site occupied by either water or a PF(6) anion in analogous complexes exhibited the highest association constant K(a) = 5.0 x 10(6) M(-1) in acetone with paraquat, 9000 times greater than the crown ether system. X-ray structures of this and analogous complexes demonstrate that improved complexation with this host is a consequence of preorganization, adequate ring size for occupation by the guest, and the proper location of the pyridyl N-atom for binding to the beta-pyridinium hydrogens of the paraquat guests. This readily accessible cryptand is one of the most powerful hosts reported for paraquats. 相似文献