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51.
Self-assembly of a new precursor [Cu(L)](ClO4)2 (1) (L = macrocyclic ligand) with octacyanometalates [M(CN)8]3- (M = Mo, W) produced two-dimensional cyano-bridged Cu(II)-M(V) bimetallic assemblies [Cu(L)]3n[M(CN)8]2n.6nH2O [M = Mo (2), W (3)] with novel honeycomblike structures, characterized by spectroscopic data, single-crystal X-ray diffraction studies, and magnetic measurements. The crystallographic determination reveals that compounds 2 and 3 are isostructural and crystallize in the triclinic system (P). The Cu atom in a distorted octahedral environment experiences a tetragonal elongation of apical nitrogen atoms exhibiting average Cu-Nax lengths of 2.566 Angstroms for 2 and 2.593 Angstroms for 3, which accounts for the Jahn-Teller effect of a Cu(II) ion. The Cu-NC angles are magnetically important, ranging from 135.7 to 159.2 degrees. Three types of L in the crystal lattice are observed, which are dependent on the relative positions of the pendant hydroxyl groups with respect to the CuN4 basal plane. The positions are correlated with hydrogen bonding of OH groups to neighboring atoms. The magnetic data indicate that ferromagnetic and antiferromagnetic interactions between Cu(II) and M(V) through the CN linkage coexist. 相似文献
52.
温敏性聚合物复合体系低临界溶解温度的研究 总被引:1,自引:0,他引:1
研究了温敏性N-异丙基丙烯酰胺的均聚物(PNIPAm)及其共聚物P(NIPAm-co-KYD)与十六烷基三甲基氯化铵(CTAC)、乙二胺四乙酸(EDTA)、盐等复配体系的低临界溶解温度(LCST)的变化规律。单因素复配体系中,wEDTA为0.1%时,体系LCST从33℃降低到25℃,增大到0.2%时,LCST下降趋于缓慢;wCTAC在0.5%-3.0%范围内,LCST先上升后下降,但wCTAC在0.5%-1.0%内相转变很不明显,超过1.5%后相转变又趋于明显;而无机盐能使体系LCST线性下降;多因素复配体系中LCST变化较缓和,易于控制且相转变现象明显。 相似文献
53.
Transmission gratings of holographic polymer-dispersed liquid crystals (HPDLC) are prepared under controlled reaction conditions by adding various amounts of chain-transfer agent (CTA). The resulting films have a higher gel content with lower cross-link density, less dark reaction, less grating shrinkage with much smoother LC/polymer interfaces, smaller induction period, and fast saturation of diffraction efficiency, which shows a maximum of 95 % with 1 % CTA. An optimum LC content of 35 % is verified on the basis of morphology and reaction kinetics. 相似文献
54.
Da Xu Zhong Lan Gao Na Li Ke An Li Key Laboratory of Bioorganic Chemistry Molecular Engineering of Ministry of Education College of Chemistry Molecular Engineering Peking University Beijing China 《中国化学快报》2007,18(5):561-564
Ru(bpy)_(3~(2 )) electrochemiluminescence (ECL) was applied to determination of rutin. ECL intensity of Ru(bpy)_(3~(2 ))could be enhanced in the presence of rutin in basic solution on platinum electrode. At pH 9.9, light emission intensity was found to be linear with rutin in the range of 1-50 mmol/L. 相似文献
55.
研究了胶原纤维固化黑荆树单宁对V(V)的吸附。采用不同温度、pH值等条件进行吸附研究,并进一步探讨了固化黑荆树单宁的吸附动力学和吸附柱动力学及其吸附机理。结果表明,该材料对V(V)的吸附平衡符合Freund lich方程,温度对吸附平衡的影响不明显;吸附动力学可用拟二级速度方程来描述,该材料同时具有良好的柱动力学特性;V(V)的吸附过程可能存在三个反应,即V(V)与吸附剂之间发生氧化还原反应生成V(IV),V(IV)和-COOH之间发生离子交换反应,以及V(IV)与单宁的邻位羟基发生螯合。 相似文献
56.
Determination of sulfite in Oriental herbal medicines 总被引:4,自引:0,他引:4
Kim YK Koh E Park SY Chang SY Park SJ Na WI Kim HJ 《Journal of AOAC International》2000,83(5):1149-1154
Sulfite was detected in 7 varieties of Oriental herbal medicines (Pueraria radix, Zingiberis rhizoma, Platycodon radix, Adenophora radix, Pinellia tuber, Astragalus radix, and Paeonia radix) on the Korean market. Sulfiting of commercial Oriental herbal medicines by fumigation with burning bituminous coal was simulated, and the accumulation of sulfite was investigated by using fresh Platycodon radix roots obtained from a growing field. The sulfite level reached a plateau in 9 h, and the maximum sulfite level found by the Monier-Williams (MW) method (AOAC 990.28) was 1020 ppm. The sulfite content in the simulated Platycodon radix sample determined by alkali extraction followed by ion-exclusion chromatography with electrochemical detection (AOAC 990.31) was approximately 17% lower on average than the MW results. Free-sulfite levels determined by acid extraction and ion-exclusion chromatography with electrochemical detection were between 19 and 49% of the MW results. The advantages of different methods for sulfite determination and the significance of the results are discussed. 相似文献
57.
Photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue was investigated using a homebuilt tandem time-of-flight mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. Efficient photodissociation of the protonated peptides was demonstrated. Most of the intense peaks in the laser-induced tandem mass spectra were sequence ions. Furthermore, sequence ions due to cleavages at all the peptide bonds were observed; this is a feature of the technique that is particularly useful for peptide sequencing. Fragmentations at both ends of the tryptophanyl residue were especially prevalent, which can be useful for location of the tryptophanyl chromophore in a peptide. 相似文献
58.
A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance. 相似文献
59.
60.
Utilization of a spiropyran derivative in a polymeric film optode for selective fluorescent sensing of zinc ion 总被引:1,自引:0,他引:1
ZHANG Ying SHAO Na YANG Ronghua LI Ke’an LIU Feng CHAN Winghong & MO Tian . College of Chemistry Molecular Engineering Peking University Beijing China . Department of Chemistry Hong Kong Baptist University Hong Kong China 《中国科学B辑(英文版)》2006,49(3):246-255
Spiropyrans are the most studied families of func- tional materials due to their reversible structural con- version in response to external optical, chemical, and thermal stimulation[1]. Irradiation with ultraviolet light causes formation of an extended π-conjugation open form (merocyanine form) by heterolytic cleavage of the C (spiro)-O bond, which generates an intense ab- sorption in the visible region. Under the irradiating of visible light, the opened form will come back to the closed spi… 相似文献