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1.
Gabelica V Galic N Rosu F Houssier C De Pauw E 《Journal of mass spectrometry : JMS》2003,38(5):491-501
A method for determining the equilibrium association constant of a complexation reaction A + B left harpoon over right harpoon AB by electrospray ionization mass spectrometry is described. The method consists in measuring the relative intensities of the peaks corresponding to A and to AB in equimolar A-B solutions at different concentrations C(0). The results are fitted by a non-linear least-squares procedure, with the two variable parameters being the equilibrium association constant K(a) and a factor R, defined by I(AB)/I(A) = R x [AB]/[A]. The factor R is the ratio between the response factors of AB and A, and corrects for the relative electrospray responses of the complex and the free substrate A, mass discrimination of instrumental origin and/or moderate in-source dissociation. The method is illustrated with the following two systems: complexes between a double-stranded 12-base pair oligonucleotide and minor groove binders, and cyclodextrin complexes with alpha,omega-dicarboxylic acids. For the oligonucleotide complexes, it is found that the response of the complex is not dramatically different to the response of the free oligonucleotide duplex, as the double helix conformation is disturbed by the drug only to a minor extent. In the case of cyclodextrin complexes, these complexes were found to have a much higher response than free cyclodextrin. This may be due to the fact that cyclodextrin is neutral in solution, whereas the complex is charged, but it can also stem from the fact that a significant proportion of the complex is in a non-inclusion geometry. The present method requires the exact determination of the concentrations of the reactants and is applicable to 1 : 1 complexes. 相似文献
2.
František Kvasnička Rudolf Ševčík Michal Voldřich Jana Krátká 《Central European Journal of Chemistry》2004,2(3):417-424
A simple and rapid capillary zone electrophoresis (CZE) method for the determination of aristolochic acid (AA) in dietary
supplements and selected herbs is described. A clear separation of AA from other sample constituents was achieved within 5
minutes without any sample clean up. A mixture of 20 mM-morpholinethanesulphonic acid+10 mM-BisTrisPropane+0.2% hydroxyethylcelullose
in 10% methanol serves as a background electrolyte. The linearity, accuracy, intra-assay and detection limit of the developed
method are 200–6000 ng/mL, 95–103%, 3.5%, and 50 ng/ml, respectively. Ease of use, sufficient sensitivity and low running
cost are the most important attributes of the CZE method. The proposed CZE method was compared with HPLC. 相似文献
3.
D. Minić Nada Štrbac I. Mihajlović Ž. Živković 《Journal of Thermal Analysis and Calorimetry》2005,82(2):383-388
In this paper, the results of copper-lead matte investigations are presented. Investigated copper-lead matte is intermediate
product of the lead production in TREPCA-Zvečan. In the first part of the paper characterization of starting material is presented,
consisting of: chemical composition analysis (XRQ), scanning electron microscopy (SEM) and diffractometry (XRD). Thermal properties
of investigated matte were determined using differential thermal analysis (DTA) at characteristic temperatures. Using results
of induced analysis, mechanism of matte oxidation process was determined. In the second part of the paper kinetic parameters
describing oxidative roasting of copper-lead matte are presented. For activation energy calculations, non-isothermal methods
defined by Kissinger and Ozawa were used [1, 2]. Kinetic equation describing oxidation process was determined using Sharps
method of reduced half time of reaction [3]. 相似文献
4.
For a noncommutative configuration space whose coordinate algebra is the universal enveloping algebra of a finite-dimensional Lie algebra, it is known how to introduce an extension playing the role of the corresponding noncommutative phase space, namely by adding the commuting deformed derivatives in a consistent and nontrivial way; therefore, obtaining certain deformed Heisenberg algebra. This algebra has been studied in physical contexts, mainly in the case of the kappa-Minkowski space-time. Here, we equip the entire phase space algebra with a coproduct, so that it becomes an instance of a completed variant of a Hopf algebroid over a noncommutative base, where the base is the enveloping algebra. 相似文献
5.
Nives Galić Nataša Burić Renato Tomaš Leo Frkanec Vladislav Tomišić 《Supramolecular chemistry》2013,25(5):389-397
The fluorescent peptidocalixarenes, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (1) and 5,11,17,23-tetra-tert-butyl-25,27-di(O-methyl)-26,28-bis(O-methyl-l-tryptophanylcarbonylmethoxy)calix[4]arene (2), were prepared by introducing tryptophan subunits at a lower calixarene rim. Coordination abilities of 1 and 2 towards Eu(III) and alkali metal cations were studied by spectrophotometric, spectrofluorimetric, conductometric and potentiometric titrations in acetonitrile at 25°C. Rather strong complexation was observed for smaller alkali metal cations Li+ and Na+ (log K Li1 >6, log K Li2 >6, log K Na1 = 8.25, log K Na2 = 6.94), and moderate for K+ (log K K1 = 5.09, log K K2 = 4.09). Larger Rb+ and Cs+ cations did not fit in the ion binding site of 1 so no complexation was detected, whereas the more flexible ligand 2 accommodated Rb+ cation (log K Rb2 = 3.44). The fluorescence of 1 (λex = 280 nm, λem = 340 nm) was remarkably quenched by Eu(III). Stability constant of 1:1 (Eu3+:1) complex determined spectrofluorimetrically amounted to log K Eu1 = 6.16. 相似文献
6.
7.
In this paper we study some mappings of skew ruled surfaces in simply isotropic space which preserve the generators. We study isometries, conformal mappings and mappings which preserve the area. Furthermore, we study mappings of surfaces in I
3
1 which preserve the asymptotic lines.Received December 18, 2001; in revised form July 12, 2002
Published online April 4, 2003 相似文献
8.
Václav Štengl Snejana Bakardjieva Natalie Murafa Eva Večerníková Jan Šubrt Vladimír Balek 《Journal of nanoparticle research》2007,9(3):455-470
A new method for preparation of titania nanowires with diameter around 10 nm and length up to 2–3 μm is described. The precursor
was prepared from sodium titanate by adding ethylene glycole (EG) and heating at temperature of 198°C for 6 h under reflux.
The sodium titanate glycolate formed by this way aggregated into 1D nanostructures and was subsequently transformed into titania
glycolate during a chemical treatment with 98% sulfuric acid. Titania nanowires with variable amount of anatase and rutile
were prepared by heating to temperatures in the range 350–1000°C. The precursor as well as titania based samples were characterized
by X-ray diffraction, Infrared spectroscopy, Scanning electron microscopy, High resolution transmission microscopy, Thermogravimetry,
Differential thermal analysis, Evolved gas analysis and Emanation thermal analysis. The nitrogen adsorption/desorption was
used for surface area and porosity determination. The photoactivity of the prepared titania samples was assessed by the photocatalytic
decomposition of 4-chlorophenol in an aqueous slurry under UV irradiation of 365 nm wavelength. 相似文献
9.
Zuzana Cibulková Andrea Černá Peter Šimon Ján Uhlár Karol Kosár Peter Lehocký 《Journal of Thermal Analysis and Calorimetry》2012,108(2):415-419
The type of cooperation between antioxidants in the binary mixtures of four substituted diphenylamines and phenotiazine in
the stabilization of styrene-butadiene rubber has been tested. Thermooxidation of the samples has been studied by differential
scanning calorimetry under non-isothermal conditions. The protection factors of the individual stabilizers and their mixtures
were determined. The synergy factors were applied to asses the type of cooperation of antioxidants in the mixtures. From their
values it can be concluded that the type of cooperation depends on temperature. The highest synergistic effect has been observed
for the mixture of phenotiazine and [4-(1-methyl-1-phenyl-ethyl)-phenyl]-phenylamine. 相似文献
10.
Tutte’s 3-Flow Conjecture suggests that every bridgeless graph with no 3-edge-cut can have its edges directed and labelled
by the numbers 1 or 2 in such a way that at each vertex the sum of incoming values equals the sum of outgoing values. In this
paper we show that Tutte’s 3-Flow Conjecture is true for Cayley graphs of groups whose Sylow 2-subgroup is a direct factor
of the group; in particular, it is true for Cayley graphs of nilpotent groups. This improves a recent result of Potočnik et al.
(Discrete Math. 297:119–127, 2005) concerning nowhere-zero 3-flows in abelian Cayley graphs. 相似文献