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241.
Gonçalves SA De Pauli SH Tedesco AC Quina FH Okano LT Bonilha JB 《Journal of colloid and interface science》2003,267(2):494-499
The counterion binding at a water/Aerosol-OT (AOT)/heptane microemulsion interface was treated in the context of the pseudo-phase ion exchange formalism. Two approaches were used to determine the selectivity coefficient for copper/sodium counterion binding at the AOT microemulsion interface: measurements of the Cu(II) concentration taken up by the reverse micelle in a Winsor II microemulsion system and steady-state emission quenching measurements of an anionic water-solubilized probe, the tris-(4,4'-dicarboxy-2,2'-bipyridine) ruthenium (II) ion. In addition, the selectivity coefficient for methyl viologen/sodium at the microemulsion surface was determined by the same photophysical technique. The value for copper (II)/sodium exchange (K(Cu/Na)) is 1.1+/-0.3 and that for methyl viologen/sodium (K(MV/Na)) is 0.9+/-0.3. The results show that the pseudo-phase ion exchange model can be used to obtain the selectivity coefficient in a microemulsion system. 相似文献
242.
M. J. Tiera V. A. De Oliveira H. D. Burrows M. Graça Miguel M. G. Neumann 《Colloid and polymer science》1998,276(3):206-212
The binding of the cations thallium(I), calcium(II) and terbium(III) to methyl methacrylate– methacrylic acid copolymers
with different fractions of acid groups (x) has been studied in aqueous solution at various pH values using the fluorescence of covalently bonded 9-vinyl anthracene
as a probe. In all cases, the extent of binding increases as a function of the charge of the polymer with either increasing
fraction of carboxylic acids or of pH. However, differences are observed in the behavior of the three cations. With Tl(I),
quenching of the anthracene group fluorescence is observed, indicating that the thallium(I) approaches the probe and suggesting
that the alkylanthracene is probably in a relatively polar region. Binding constants have been determined from anthracene
quenching data and from studies with the fluo-rescent-probe sodium pyrenetetra-sulfonate. Good agreement is obtained between
the two methods, and values for the binding constants increase from 250 to 950 M-1 as x increases from 0.39 to 1. It is suggested that the cation is held in the polyelectrolyte domain, partly by Debye–Hückel effects
and partly by more specific interactions. Stronger binding is found with calcium(II) and terbium(III), and in this case increases
in fluorescence intensity are observed on complexation due to the anthracene group being in a more hydrophobic region, probably
as a result of conformational changes in the polymer chain. In the former case the stoichiometry of the interaction was determined
from the fluorescence data to involve two carboxylate groups bound per calcium. Association constants were found using murexide
as an indicator of free calcium to vary from 8400 to 37 000 M-1 as x increases from 0.39 to 1. It is suggested that in this case specific calcium(II)–carboxylate interactions contribute to the
binding. With terbium(III), a greater increase in the probe fluorescence intensity was observed than with calcium, and it
is suggested that the interaction with the polymer is even stronger, leading to a more pronounced conformational change in
the polymer. It is proposed that the terbium(III) interacts with six carboxylic groups on the polymer chain, with three being
coordinated and three attracted by electrostatic interactions.
Received: 10 June 1997 Accepted: 24 October 1997 相似文献
243.
Budimir N Fournier F Bailly T Burgada R Tabet JC 《Rapid communications in mass spectrometry : RCM》2005,19(13):1822-1828
The tripodal ligand N,N,N-tris[(1,hydroxy-2-pyridinon-6-yl)amide]propylamine was synthesized. It is composed of an anchor (nitrogen atom), a functional group (hydroxamate), and also a spacer of variable length defined by the number of methylene groups linking the anchor and the functional group. The characterization of this ligand in the presence of several divalent metal cations (Fe(II), Mn(II), Co(II) and Cu(II)), performed by electrospray ionization mass spectrometry (ESI-MS and ESI-MS/MS), allowed elucidation of oxidation states and also of different fragmentation patterns. The importance of the spacer length was studied in the case of the iron binary complex by comparing this ligand with another with a shorter spacer. In this way the stabilizing conditions, in which hydrogen bonds are implicated, were clarified. 相似文献
244.
Using cyclodextrin-capillary zone electrophoresis (CD-CZE), baseline separation of baclofen phaclofen, saclofen, and hydroxy-saclofen, potent gamma-aminobutyric acid(B) (GABA(B)) agonist or antagonists was achieved. A method for the enantioresolution of those analogs of GABA was developed using anionic cyclodextrins (highly sulfated CD or highly S-CD) as chiral selectors and capillaries dynamically coated with polyethylene oxide (PEO). With charged CDs we observed good resolutions due to the large electrophoretic mobility of these chiral selectors opposite to the mobility of the solutes. The highly S-alpha-CD and S-beta-CD were found to be complementary and the most effective complexing agent, allowing good enantiomeric resolution in short runtimes. The complete resolution was obtained using 25 mM phosphate buffer at pH 2.5 containing 3% w/v of highly S-alpha-CD or S-beta-CD at 25 degrees C with an applied field of 0.30 kV/cm. The apparent binding constants of the inclusion complexes were evaluated and the migration order was determined. A comparison was possible to investigate the importance of the anionic group of the molecules in the separations. The pK(a) values were determined for all four compounds in order to explain relative electrophoretic migration of the solutes. 相似文献
245.
A rapid and sensitive RP-HPLC method with UV detection at 305 nm for routine quality control of entacapone in tablets was developed. The procedure was validated by specificity, robustness, linearity, accuracy, repeatability and intermediate precision. Experimental design was used during validation to calculate method robustness. The method employs an Ace RP-18 (250 × 4.6 mm i.d., particle size 5 μm), with a mobile phase consisting of water pH 3.0: acetonitrile (65:35, v/v). Entacapone solutions were exposed to direct UV radiation (254 nm), alkaline hydrolysis, acid hydrolysis and effect of oxidation by hydrogen peroxide to evaluate method stability-indication and peak purity tool was utilized to verify the peak purity. The results confirm that the method is highly suitable for its intended purpose. 相似文献
246.
Maurice Guillot André Marchand François Tcheou H. Le Gall 《Zeitschrift für Physik B Condensed Matter》1982,49(3):221-228
On single crystals of holmium iron garnet (HoIG), magnetic properties have been studied in magnetic field up to 150kOe applied parallel to the main crystallographic directions in the 4.2–300K temperature range. Above 130 K, the magnetization is isotropic and linear magnetic field dependent as previously found in polycrystals and predicted by Néel's ferrimagnetic theory. Nevertheless the paramagnetic Curie temperature is much higher than the polycrystal value. Below 130K, due to the onset of the umbrella structure, the ferrite magnetization presents a non linear field variation with [111] as easy direction. The field evolutions of the anisotropy constants (K
1 andK
2) were calculated. Optical absorption measurements of both 585I
6 and 5I
85I
7 transitions are reported and compared to the results of the literature in terms of inequivalent magnetic sites. 相似文献
247.
In this review, we discuss a number of computational methods that have been developed or adapted for molecule classification and virtual screening (VS) of compound databases. In particular, we focus on approaches that are complementary to high-throughput screening (HTS). The discussion is limited to VS methods that operate at the small molecular level, which is often called ligand-based VS (LBVS), and does not take into account docking algorithms or other structure-based screening tools. We describe areas that greatly benefit from combining virtual and biological screening and discuss computational methods that are most suitable to contribute to the integration of screening technologies. Relevant approaches range from established methods such as clustering or similarity searching to techniques that have only recently been introduced for LBVS applications such as statistical methods or support vector machines. Finally, we discuss a number of representative applications at the interface between VS and HTS. 相似文献
248.
The thermal behaviours of the Ti(II), Mn(II), Fe(II), Ni(II), Cu(II) and Zn(II) complexes of triethanolamine were studied by means of thermogravimetry, differential thermogravimetry, differential thermal analysis infrared spectrophotometry and elemental analysis. The sequence of thermal stability of the metal complexes, determined by using the initial decomposition temperature, was found to be Ti(II)?Mn(II)>Fe(II)>Ni(II)>Zn(II)>Cu(II). Some of the kinetic parameters, such as the activation energy and order of reaction for the initial decomposition reaction, were calculated and the relationship between the thermal stability and the chemical structure of the complexes is discussed. 相似文献
249.
Haneline MR Taylor RE Gabbaï FP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(21):5189-5193
Trimeric perfluoro-ortho-phenylenemercury (1) constitutes one of the simplest trifunctional Lewis acidic hosts. In addition to cooperative effects arising from the proximity of the mercury(II) centers, the electron-withdrawing properties of the backbone and the accessibility of the electrophilic sites lead to the facile complexation of neutral and electron rich substrates. The planarity of the structure as well as its overall polarizability compounded with relativistic effects at mercury also permits the occurrence of non-covalent interactions and accounts for the tendency of this compound to form cofacial dimers. Collectively, the Lewis acidic properties of 1 as well as its ability to engage in non-covalent interactions can be held responsible for its ability to form extended binary supramolecular stacks with arenes. The photoluminescence observed in some of these supramolecular complexes corresponds to the phosphorescence of the aromatic substrate and indicate the occurrence of a mercury heavy atom effect. 相似文献
250.
Gohy JF Lohmeijer BG Schubert US 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(15):3472-3479
The formation of asymmetric bis-complexes, based on terpyridine ligands and ruthenium ions, is described as a powerful tool for the self-assembly of polymer blocks end-functionalized with terpyridine units. This is illustrated in this contribution for the synthesis of amphiphilic metallo-supramolecular block copolymers, which are further used to produce aqueous micelles. Finally, the reversibility of the supramolecular bond opens new avenues for the preparation and manipulation of these nano-objects. 相似文献