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排序方式: 共有382条查询结果,搜索用时 15 毫秒
1.
Boseggia E Gatos M Lucatello L Mancin F Moro S Palumbo M Sissi C Tecilla P Tonellato U Zagotto G 《Journal of the American Chemical Society》2004,126(14):4543-4549
A series of cis-cis-triaminocyclohexane Zn(II) complex-anthraquinone intercalator conjugates, designed in such a way to allow their easy synthesis and modification, have been investigated as hydrolytic cleaving agents for plasmid DNA. The ligand structure comprises a triaminocyclohexane platform linked by means of alkyl spacers of different length (from C(4) to C(8)) to the anthraquinone group which may intercalate the DNA. At a concentration of 5 microM, the complex of the derivative with a C(8) alkyl spacer induces the hydrolytic stand scission of supercoiled DNA with a rate of 4.6 x 10(-6) s(-1) at pH 7 and 37 degrees C. The conjugation of the metal complex with the anthraquinone group leads to a 15-fold increase of the cleavage efficiency when compared with the anthraquinone lacking Zn-triaminocyclohexane complex. The straightforward synthetic procedure employed, allowing a systematic change of the spacer length, made possible to gain more insight on the role of the intercalating group in determining the reactivity of the systems. Comparison of the reactivity of the different complexes shows a remarkable increase of the DNA cleaving efficiency with the length of the spacer. In the case of too-short spacers, the advantages due to the increased DNA affinity are canceled due to the incorrect positioning of the reactive group, thus leading to cleavage inhibition. 相似文献
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A simplified form of the first-order many-body theory was used for the calculation of the coherence and correlation parameters for the excitation of the 21 P and 31 P states of helium. The excited state wave functions were calculated numerically in the fixed core Hartree-Fock(HF) approximation. The ground state wave function was used in the HF approximation. Scattering orbitals were calculated numerically in the static exchange approximation. Calculations were performed forE=29.6, 40, 50, 60 and 80 eV impact energies for the 21 P state, and forE=50 eV and 80 eV for the 31 P state. Results for the coherence and correlation parameters are compared with the experimental values obtained from electronphoton coincidence experiments, and with other theoretical results. 相似文献
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The electrochemical reduction of antifouling agent 2-thiocyanomethylthiobenzothiazole (TCMTB) was investigated by cyclic and pulse differential voltammetry. The irreversible electrode reduction of TCMTB proceeded by ECEC reaction mechanism by two electrons transfer with one irreversible wave. Upon the basis of electrochemical evidence, the electrodic reaction mechanism was suggested to formation of mercaptobenzothiazole (MTB) in solution.Subsequently, a pulse differential method is described for the formation of TCMTB based on this electroreduction. Having been obtained a detection limit of 1.0 × 10−7 mol L−1 and recovery to 98% to concentration of 2.0 × 10−6 mol L−1. Therefore, the proposed method in this study is practical, sensitive and accurate for the analysis of TCMTB in tannery wastewater samples. 相似文献
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G. D. Meneses L. M. Brescansin M. -T. Lee S. E. Michelin L. E. Machado G. Csanak 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1994,30(2):173-175
We have applied the density matrix formalism and the distorted-wave approximation to calculate the Stokes parameters for thed 3 Π u ? (v=0,1,2,3;N=1) states of H2 excited from the X1 ∑ g + (v=0,N=1) state by electron impact at the incident energies ranging from 15 to 40 eV. Our results show that these parameters are nearly independent of the vibrational quantum number of the excited states. However, the polarization of the radiation emitted by the target in the subsequent decay process increases with increasing incident energies. 相似文献
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Sanchiz J Esparza P Villagra D Domínguez S Mederos A Brito F Araujo L Sánchez A Arrieta JM 《Inorganic chemistry》2002,41(23):6048-6055
The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-tetraacetate (3,4-TDTA), o-phenylenediamine-N,N,N',N'-tetraacetate (o-PhDTA), and 4-chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetate (4-Cl-o-PhDTA) (H4L acids) toward lead(II) is studied by potentiometry (25 degrees C, I = 0.5 mol x dm(-3) in NaClO4), UV-vis spectrophotometry, and 207Pb NMR spectrometry. The stability constants of the complex species formed were determined. X-ray diffraction structural analysis of the complex [Pb4(mu-3,4-TDTA)4(H2O)2]*4H2O (1) revealed that 1 has a 2-D structure. The layers are built up by the polymerization of centrosymmetric [Pb4L2(H2O)2] tetranuclear units. The neutral layers have the aromatic rings of the ligands pointing to the periphery, whereas the metallic ions are located in the central part of the layers. In compound 1, two types of six-coordinate lead(II) environments are produced. The Pb(1) is coordinated to two nitrogen atoms and four carboxylate oxygens from the ligand, whereas Pb(2) has an O6 trigonally distorted octahedral surrounding. The lead(II) ion is surrounded by five carboxylate oxygens and a water molecule. The carboxylate oxygens belong to four different ligands that are also joined to four other Pb(1) ions. The selective uptake of lead(II) was analyzed by means of chemical speciation diagrams as well as the so-called conditional or effective formation constants K(Pb)eff. The results indicate that, in competition with other ligands that are strong complexing agents for lead(II), our ligands are better sequestering agents in acidic media. 相似文献
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Thomas Glonek Patricio Meneses 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1-4)
Abstract Cell membrane phospholipids can be identified and quantitated using 31P NMR spectroscopy in conjunction with an analytical reagent composed of chloroform-benzene(d6)/methanol-CsEDTA 2:l ml/ml. 3 ml of this reagent dissolves between 0.01–100 mg crude tissue lipids obtained by the Folch procedure. When the source phospholipids are strongly contaminated with cations, it is necessary to modify the extraction method, backwashing with K-EDTA, 0.6 M, pH 6, instead of KC1. Also if source tissues must be stored for long periods of time, acetone desication is recommended. Using a 500 MHz 31PNMR spectrophotometer (magnetic field ?11.75 T), the extracted phospholipids yield narrow Lorenzian signals (1.8–3.2 Hz at half-height), with these widths at half-height corresponding to their 1/πT2 values. Chemical shifts (δ) at 24 °C, following the IUPAC shift convention and relative to 85% phosphoric acid, were determined as follows:CAEP,21.09;LPG,l,O9;LPA,0.83;LPE plas,0.53;PG,0.50;LPE,0.43; PA,0.25;CL,0.18;LPI,0.10;PE plas,0.07;PE,0.03;PS,?0.O5;SPH,?0.O9; DiMePE,?b.18;LPC plas,?0.20;LPC,?0.28;PI,?0.37; PAF, ?0.70;PC plas,?0.77; PC, ?0.84. This reagent permits assays of high precision and accuracy that use little spectrometer time and that are suitable for automated procedures. 相似文献
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