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971.
HUA Er-BingCoordination Chemistry Institute State Key Laboratory of Coordination Chemistry Nanjing University Nanjing Jiangsu ChinaYANG Pin LI Qing-Shan YANG Bin-ShengInstitute of Molecular Science Shanxi University Taiyuan Shanxi China 《中国化学》1996,14(4):297-302
The effect of Cu2+ on the triple-stranded helical structure of poly(A:2I) was studied by means of circular dichroism spectral method with the help of ultraviolet spectral and ethidium bromide fluorescence probe methods. It was found that Cu2+ destabilizes the structure of the triple helix poly(A:2I) and induces its structural transformations, meanwhile, the transformations can be partially reversed by a higher NaCl concentration. The structural transformations may be expressed by the following scheme: poly(A:2I) - poly(A:I) + poly(I)- poly(A) + 2poly(I) 相似文献
972.
Summary Fringelite D was synthesized from 1,3,6,8-tetramethoxyanthracen-9-olvia two different efficient routes. The first one involved demethylation and subsequent dimerization. The other one started with dimerization to yield octamethylfringelite D and subsequent demethylation. The starting material was prepared in four steps from commercially available educts, the key step being a benzamideortho-lithiation. The spectroscopic properties of fringelite D were measured and are discussed. The dissociation, deprotonation, and protonation equilibria of fringelite D were characterized by their respectivepK values in ground and excited states and compared with those of hypericin. Homo- and heteroassociation properties of fringelite D were found to be similar to those of hypericin.
Synthese und Eigenschaften von Fringelit D (1,3,4,6,8,10,11,13-Octahydroxy-phenanthro[1,10,9,8,o,p,q,r,a]perylen-7,14-dion)
Zusammenfassung Fringelit D wurde auf zwei effizienten Routen aus 1,3,6,8-Tetramethoxyanthracen-9-ol synthetisiert. Die erste umfaßt Demethylierung und anschließende Dimerisierung. Die andere beginnt mit der Dimerisierung zu Octamethylfringelit D und endet mit einer Demethylierung. Das Ausgangsmaterial wurde in vier Stufen aus kommerziell zugänglichen Edukten dargestellt; der Schlüsselschritt ist eineortho-Lithiierung eines Benzamids. Die spektroskopischen Eigenschaften von Fringelit D wurden gemessen und werden diskutiert. Die Dissoziations-, Deprotonierungs- und Protonierungsgleichgewichte wurden durch ihrepK-Werte in Grundzustand und angeregtem Zustand charakterisiert und mit jenen des Hypericins verglichen. Die Homo- und Hetero-assoziationseigenschaften von Fringelit D sind jenen des Hypericins ähnlich.相似文献
973.
Samuel Melaku Rita Cornelis Frank Vanhaecke Richard Dams Luc Moens 《Mikrochimica acta》2005,150(3-4):225-231
A simple, sensitive and inexpensive method for the speciation of Cr(VI) and Cr(III) in river and industrial wastewater was developed, optimized and validated. Samples were collected, filtered and then chromium species were determined in the filtrate. In the filtrate, total Cr was determined directly by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). A portion of the filtered sample was buffered to pH 6.4, extracted with Amberlite LA-2/MIBK and finally Cr(VI) was determined in the organic extract and Cr(III) in the aqueous phase using GFAAS. The method was evaluated by analysis of the certified reference material, CRM 544, and good accuracy was obtained. The limit of detection for Cr(VI) and Cr(tot)/Cr(III) was found to be 0.30 and 0.08 µg L−1, respectively, and a precision expressed as relative standard deviation of better than 11% was achieved for nine replicates. A number of water samples from the Tinishu Akaki River, Ethiopia, and wastewater samples from a chemical plant in Germany, were analysed. In addition to the GFAAS method, Cr(tot) was also determined using ICP-MS (in CRM 544, lyophilized water, and Tinishu Akaki River water samples) and Cr(tot) and Cr(VI) using UV-VIS spectrophotometry (in CRM 544 and industrial wastewater samples). Good agreement between the different methods was found. 相似文献
974.
A novel sensitive method for the determination of nucleic acid (DNA) using the resonance light scattering (RLS) spectra of pentamethoxyl red has been developed. It is based on the effects on the resonance light scattering of Pentamethoxyl Red. The effective factors and the optimum conditions were studied, and the enhanced intensity of RLS is in proportion to the concentration of nucleic acids in the range of 0–2.54 µg mL−1 for ct-DNA, 0–4.54 µg mL−1 for hs-DNA. The limits of detection are 1.1 and 2.1 ng mL−1, respectively. Most foreign substances do not interfere in the determination, and the method has good selectivity and high sensitivity. It has been applied to the determination of DNA in synthetic samples and in real samples with satisfactory results. 相似文献
975.
油菜花粉十二肽的二维核磁共振研究 总被引:4,自引:0,他引:4
用核磁共振方法对油菜花粉十二肽溶液构象进行了研究。利用2D COSY和NOESY归属了^1H NMR谱的全部共振峰。用Karplus方程从肽键N-H质子与α-H质子的偶合常数计算出了所有肽键的二面角θ及Φ,并对其进行不同温度及不同溶剂条件下的观测。结果表明,在水溶液中该肽链为无规卷曲结构,个别肽段存在γ-turn构象。 相似文献
976.
José A. Rodriguez 《Theoretical chemistry accounts》2002,107(3):117-129
The surface chemistry of oxides is relevant for many technological applications: catalysis, photoelectrolysis, electronic-device
fabrication, prevention of corrosion, sensor development, etc. This article reviews recent theoretical works that deal with
the surface chemistry of oxides. The account begins with a discussion of results for the adsorption of CO and NO on oxides,
systems which have been extensively studied in the literature and constitute an ideal benchmark for testing the quality of
different levels of theory. Then, systematic studies concerned with the behavior of adsorbied alkali metals and sulfur-containing
molecules are presented. Finally, a correlation between the electronic and chemical properties of mixed-metal oxides is analyzed
and basic principles for designing chemically active oxides are introduced. Advances in theoretical methods and computer capabilities
have made possible a fundamental understanding of many phenomena associated with the chemistry of molecules on oxide surfaces.
Still many problems in this area remain as a challenge, and the approximate nature of most theoretical methods makes necessary
a close coupling between theory and experiment. Following this multidisciplinary approach, the importance of band-orbital
interactions for the reactivity of oxide surfaces has become clear. Simple models based on band-orbital mixing can explain
trends found for the interaction of many adsorbates with oxide surfaces. These simple models provide a conceptual framework
for modifying or controlling the chemical activity of pure oxides and for engineering mixed-metal oxides. In this respect,
theoretical calculations can be very useful for predicting the best ways for enhancing the reactivity of oxide systems and
reducing the waste of time, energy and materials characteristic of an empirical design.
Received: 21 June 2001 / Accepted: 8 October 2001 / Published online: 1 February 2002 相似文献
977.
Preparation,stability and two-dimensional ordered arrangement of gold nanoparticles capped by surfactants with different chain lengths 总被引:2,自引:0,他引:2
Gold nanoparticles modified with C10NH2, C12NH2, C16NH2 and C18NH2 respectively have been prepared by the reverse micelle method. Nanoparticles stability and their two-dimensional (2D) ordered arrangement were studied by UV-Vis absorption spectra and LB technique. The factors, such as the chain length and the size distribution of particles, which affect the 2D ordered arrangement formation, are discussed. Experimental results show that the longer the chain length of surfactants capping the gold nanoparticles, the more stable the nanoparticles, and the more ordered 2D arrangement of gold nanoparticles. 相似文献
978.
The comparison of a pure electrostatic approximation and complete supermolecule SCF ab initio computations on the hydration scheme of uracil and cytosine shows that the electrostatic procedure is capable to reproduce the general aspects of the results of the supermolecule treatment provided that different distances of shortest approach be adopted for the distances between the oxygen of water and the nitrogen of NH2 or NH groups or the oxygen of C-O groups on the one hand and the oxygen of water and pyridine-type nitrogens on the other hand. 相似文献
979.
Rubén Montalvo-González 《Journal of Molecular Structure》2003,655(3):375-389
The complete 1H, 13C and 15N NMR analyses for a series of 25 diaryl-aldimines containing phenyl, pyridyl, pyrazolone and furanyl moieties are described herein. Detailed evaluation of substituent chemical shift and coupling constant effects showed that interaction between the lone pair of the pyrazolone carbonyl group or the nitrogen of 2-substitued pyridines with the aldimine hydrogen increases the value and shifts the resonance signal for this hydrogen to high frequency, in the 1H NMR spectra. The X-ray crystal structure analysis of pyrazolone substituted aldimines evidenced the planarity of the aryl groups which are conjugated with the CN double bond. In the case of the N-(2-pyridinemethylene)-1,5-dimethyl-2-phenyl-1,2-dihydro-pyrazol-3-one, two rotamers were observed in the same unit cell. 相似文献
980.
《Arabian Journal of Chemistry》2020,13(12):8848-8887
Phthalocyanine (Pc) complexes are an important class of dyes with numerous (e.g., biological, photophysical, and analytical) applications. Among the methods used to improve the properties of these complexes, one should mention the introduction of different substituents, variation of the central metal ion, ligand exchange, and conjugation to nanomaterials (e.g., carbon-based nanomaterials and metal nanoparticles (NPs)). This work briefly reviews Pc complex conjugation to Ag and Au NPs, highlights the different NP shapes, and discusses the diversity of conjugation approaches. Moreover, the use of UV–Vis spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy, dynamic light scattering and Fourier transform infrared spectroscopy to characterize Pc-NP hybrids is summarized. The effect of conjugation on Pc photo-physicochemical properties (fluorescence, singlet oxygen generation, triplet state formation, and optical limiting behavior) is discussed, and future perspectives for the synthesis and applications of new hybrids are provided. 相似文献