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991.
在增溶剂存在下硫氰酸盐-结晶紫光度法测定微量钨 总被引:3,自引:0,他引:3
在明胶存在下,钨与硫氰酸盐和结晶紫生成可溶性三元缔合物,最大吸收波长为540nm,表现摩尔吸光系数为4.1×10~5 L·mol~(-1)·cm~(-1),钨在0~11μg/25ml范围内服从比尔定律。方法已用于测定岩石中微量钨。 相似文献
992.
993.
In order to explore the transfer mechanism of chromium(III) in mammals, a novel complex [Cr(ASA)(en)2]Cl· 2H2O, bis(ethylenediamine‐ κ 2 N,N′)(4‐aminosalicylic acid‐ κ 2 O,O′) chromium(III) monochloride dihydrate was synthesized (4‐aminosalicylic acid=H2ASA, ethylenediamine=en). The crystal structure belongs to orthorhombic system with the space group P212121 by means of X‐ray diffraction. The characteristic for transfer of Cr3+ from the compound to the low‐molecular‐mass chelator EDTA and the iron‐binding protein apoovotransferrin (apoOTf) was followed by UV‐visible (UV‐Vis) and fluorescence spectra in 0.01 mol·L?1 Hepes at pH 7.4. The second order rate constants were calculated. Those spectra in conjunction were used to obtain more accurate information about the interaction of chromium complex with apoOTf. The experimental results indicate that Cr3+ can be transferred from the complex to apoOTf with the retention of the 4‐aminosalicylic acid acting as a synergistic anion. 相似文献
994.
An operationally simple oxidative methyl esterification of primary alcohols in good yields using an iodine‐mediated poly[4‐(diacetoxyiodo)styrene] in methanol at room temperature is described. The polymeric reagent can be regenerated and reused as an environmentally benign reagent. 相似文献
995.
Investigation of the root extract of Antidesma pentandrum var. barbatum led to the isolation of seven new compounds, antidesmol ( 1 ), antidesmanins E ( 2 ) and F ( 3 ), antidesnone ( 4 ), antidesnol ( 5 ), barbatumols A ( 6 ) and B ( 7 ), together with 14 known compounds including sodium aristolochate‐I ( 10 ) and aristolochic acid‐I methyl ester ( 11 ). 相似文献
996.
The gel effect in the reactive extrusion process for free radical polymerization in a closely intermeshing co‐rotating twin screw extruder was investigated. First the reaction kinetic model was constructed mainly on the basis of entanglement theory. Next, numerical calculation expressions for the initiator and monomer concentrations, monomer conversion, average molecular weight and apparent viscosity were deduced. Finally, the evolution of the above variables were shown and discussed for the example of butyl methacrylate. The simulated results of the monomer conversion are in good agreement with experimental results.
997.
Ji‐Jiang Wang Meng‐Lin Yang Huai‐Ming Hu Prof. Dr. Gang‐Lin Xue Dong‐Sheng Li Qi‐Zhen Shi 《无机化学与普通化学杂志》2007,633(2):341-345
To determine the influence of the size of the aromatic chelate ligands on the frameworks of metal tretracarboxylate polymers, two new coordination polymers [Cd(btc)0.5 (2,2′‐bpy)] ( 1 ) and [Cd(btc)0.5(phen)]·H2O ( 2 ) (H4btc = biphenyl‐3,3′,4,4′‐tetracarboxylic acid, 2,2′‐bpy = 2,2′‐bipyridine, phen = 1,10‐phenanthroline) have been synthesized under similar hydrothermal conditions. In complex 1 , the dimeric Cd2 units are linked by bridging btc4? ligand to form a 2D layered network, whereas complex 2 possesses a 3D metal‐organic framework consisting of the dimeric Cd2 units. The differences of two metal‐organic frameworks demonstrate that the size of the rigid aromatic chelate ligands have an important effect on the structures of their complexes. Additionally, the two complexes show strong fluorescence in the solid state at room temperature. 相似文献
998.
The electrochemical behavior and the interaction of alizarin red S (ARS) with calf thymus DNA was investigated on a bare glassy carbon electrode (GCE) and DNA modified GCE (DNA/GCE), respectively. ARS showed a pair of redox peaks at ?0.445 V and ?0.414 V on a bare GCE. On addition of DNA into the ARS solution, the peak current of ARS decreased and the peak potential positively shifted, but without new redox peaks appeared. The ARS reduction peak current increased with immersion time on a DNA/GCE. The results showed that ARS could interact with DNA molecules by intercalative binding mode. The equilibrium constant, binding number and the ratio of binding constant for oxidized and reduced ARS forms were obtained. The DNA damage was directly detected by appearance of guanosine and adenosine bases oxidation signal. The influence of experimental conditions on DNA damage extent was discussed in detail. 相似文献
999.
Ya‐Ching Shen Yun‐Sheng Lin Shaw‐Man Hsu Ashraf Taha Khalil Shih‐Sheng Wang Ching‐Te Chien Yao‐Haur Kuo Chang‐Hung Chou 《Helvetica chimica acta》2007,90(7):1319-1329
The phytochemical investigation of the more polar fractions from the leaves and twigs of Taxus sumatrana (Taxaceae) afforded five new taxane diterpene esters, tasumatrols P–T ( 1 – 5 ) possessing an 11(15→1),11(10→9)‐diabeotaxane skeleton. Compounds 1, 4 , and 5 contain an α‐hydroxy group at C(14), while 3 has no OH group at either C(13) or C(14). Compound 2 is a natural 4,5‐acetonide derivative, while 4 has an unusual spiro‐connected 2‐hydroxy‐2‐phenyl‐1,3‐dioxolane ring. Ten known taxoids, were also isolated in the course of the chromatographic fractionation. Five additional new O‐acetyl derivatives 3a, 4a, 4b, 5a , and 5b were prepared from the taxanes 3 – 5 . The structures of all new compounds were established on the basis of their spectroscopic analyses. Compound 1 showed mild cytotoxic activity against human Hela and Daoy tumor cells. 相似文献
1000.
Chun Lei Sheng‐Xiong Huang Ji‐Jun Chen Jian‐Xin Pu Li‐Mei Li Wei‐Lie Xiao Jin‐Ping Liu Li‐Bin Yang Han‐Dong Sun 《Helvetica chimica acta》2007,90(7):1399-1405
Four new, highly oxygenated nortriterpenoids with the unique schisanartane skeleton, propindilactones A–D ( 1 – 4 ), were isolated from the aerial parts of Schisandra propinqua var. propinqua, together with four known schisanartane‐type compounds. The structures of the new plant constituents were established on the basis of extensive spectroscopic methods. 相似文献