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31.
The "palladiazo" reagent has been subjected to a detailed spectrophotometric investigation in concentrated perchloric acid, different aqueous buffers and concentrated sodium hydroxide solutions. K(1)-K(10) and (1)-(10) values corresponding to the instability constants of the protolytic equilibria involved and to the molar absorptivities at 540 and 630 run of the different proton complex species of the system have been calculated by a number of analytical and graphical spectrophotometric methods. Special attention has been paid to the study of the complicated phenomena implied by the interaction of the reagent with perchloric acid, which has been shown to give rise to alteration of the initial isomeric composition of the reagent and to the formation of addition and/or oxidation products derived from side-reactions undergone by the reagent with the medium. All the instability constants and molar absorptivities, which have been determined by several methods, are tabulated for comparison. 相似文献
32.
The possibility of coulometric titrations of cysteine, 2-thio-uracil, 6-mercaptopurine, and 6-thioguanine with iodine and bromine in methanol and with bromine in acetic acid has been investigated. Conditions have been found for the direct titration of the test substances with iodine in methanol based on their 1-electron oxidation to the corresponding disulphides and for their direct and indirect determination with bromine in acetic acid based on their 6-electron oxidation to the corresponding sulphonic acids.On leave from Department of Analytical Chemistry, Charles University, Prague, Czechoslovakia 相似文献
33.
Crowe MC Kapoor RN Cervantes-Lee F Párkányí L Schulte L Pannell KH Brodbelt JS 《Inorganic chemistry》2005,44(18):6415-6424
Electrospray ionization (ESI) quadrupole ion trap mass spectrometry (QIT-MS) and collisionally activated dissociation (CAD) were used to evaluate the rare-earth binding properties of two hydrophobic carbamoylmethylphosphine oxide (CMPO) ligands, the normal bidentate variety, (t-BuC6H4)2P(O)CH2C(O)N(i-Bu)2 (A), a new potentially tridentate extractant, (t-BuC6H4)2P(O)CH[CH2C(O)N(i-Bu)2]C(O)N(i-Bu)2 (B), and tributyl phosphate. The mass spectral results obtained from analysis of 1% HNO3/methanol solution containing the ligands and dissolved lanthanide salts reveal that the favorable stoichiometries of the ligand/metal/nitrate complexes are 2:1:2 for the bidentate ligand A, 1:1:2 for the tridentate ligand B, and 3:1:2 for the monodentate tributyl phosphate. These observed stoichiometries correlate with the number of available binding sites on each ligand as well as with potential steric effects. Energy-variable collisionally activated dissociation experiments showed that for the 2:1:2 complexes involving ligand A or B, as the ionic radius of the bound metal decreased, the removal of nitric acid required less energy and resulted in less extensive spontaneous solvent coordination. This experimental trend suggests that, as the ionic radius of the lanthanide ion decreases, a pair of the carbamoylmethylphosphine ligands is able to more completely solvate the bound metal ion thereby weakening the nitrate-metal interaction. 相似文献
34.
Ludvík Beneš Klára Melánová Vítězslav Zima Jaroslava Kalousová Jiří Votinský 《Journal of inclusion phenomena and macrocyclic chemistry》1998,31(3):275-286
Recent knowledge of the kinetics and intercalation mechanisms are summarized and accompanied by examples of intercalation reactions of water and ethanol into anhydrous vanadyl phosphate and redox intercalation of alkali metal cations into vanadyl phosphate dihydrate. Three possible mechanisms of intercalation are presented which are based on: (i) a concept of exfoliation of layers; (ii) the formation of stages and randomly stacked layers; (iii) co-existence of intercalated and non-intercalated parts of crystals of the host separated by an advancing phase boundary. The corresponding kinetic curves are ascribed to mechanisms (ii) and (iii). 相似文献
35.
García-Raso A Fiol JJ Tasada A Albertí FM Molins E Basallote MG Máñez MA Fernández-Trujillo MJ Sánchez D 《Dalton transactions (Cambridge, England : 2003)》2005,(23):3763-3772
Alkylidene-bis(2-aminopyrimidines) (pyr2Cx, x = 2-5) are useful ligands to interact with Ag(I) yielding discrete metallocycles. Crystal structures of the [(pyr2C2)Ag(NO3)]2 and [(H-pyr2C4)Ag(NO3)2]2 have been isolated where each macrocyclic moiety interacts with their surroundings through weak interactions, yielding 3D discrete structures, On the other hand, the solution study shows that the equilibrium constants for the formation of Ag(pyr2Cx)+ complexes are higher than the literature values for Ag(I) complexes with single pyrimidines, although the differences could be explained by invoking the solid-state structures of the Ag(I)-pyr2Cx complexes. 相似文献
36.
We describe the synthesis and photophysical properties of a series of neutral and cationic 3,4-tetrapyridinoporphyrazines, potential lead photosensitizers for photodynamic inactivation of bacteria. Tetracationic TPyPzs exist essentially as monomers in aqueous systems, but the presence of trialkylated compounds due to incomplete quaternization of the outer nitrogen atoms induces severe aggregation. The absorption, fluorescence, triplet, and singlet oxygen quantum yields for both the neutral and cationic compounds are comparable to those of the related phthalocyanines. 相似文献
37.
Gil-Agustí M Carda-Broch S García-Alvarez-Coque MC Esteve-Romero J 《Journal of chromatographic science》2000,38(12):521-527
An ODS-2 column, a micellar mobile phase of high elution strength containing 0.1M sodium dodecyl sulfate and 3% (v/v) butanol, and ultraviolet detection at 230 nm are used for the determination of either of two benzodiazepines (clorazepate and diazepam) and a benzothiazepine (diltiazem) in pharmaceuticals. The procedure is shown to be competitive against conventional chromatography with methanol-water mobile phases, especially for diltiazem. The composition of the micellar mobile phase is selected using a predictive strategy based on an accurate retention model and assisted by computer simulation. Calibration graphs are linear at least in the 2.5 to 20 microg/mL, 4 to 20 microg/mL, and 5 to 40 microg/mL ranges for clorazepate, diazepam, and diltiazem, respectively. The intra- and interday repeatabilities (%) are clorazepate (1.7, 5.2), diazepam (0.43, 3.7), and diltiazem (0.36, 3.1). Limits of detection are well below the concentrations of the drugs found in the commercial pharmaceutical preparations analyzed. The drug contents evaluated with the proposed procedure are compared with the declared contents given by the manufacturers. The achieved percentages of label claim are usually between 95 and 104%. 相似文献
38.
The flow injection analyzer for students, teaching and research (FIAstar) is used in conjunction with a new micropool mercury flow-through electrode, to explore the possibilities offered by using d.c. polarography, rapid scan and amperometric titrations on a dispersed sample zone in motion. The work outlines the principles of the use of a scanning detector for investigation of the concentration gradients and chemical reactions taking place during the dispersion of sample solution within a carrier stream. The data, which are collected in real time, are displayed in three-dimensional diagrams. 相似文献
39.
Martí M Barsukov LI Fonollosa J Parra JL Sukhanov SV Coderch L 《Langmuir : the ACS journal of surfaces and colloids》2004,20(8):3068-3073
Despite the promising application of liposomes in wool dyeing, little is known about the mechanism of liposome interactions with the wool fiber and dyestuffs. The kinetics of wool dyeing by two dyes, Acid Green 27 (hydrophobic) and Acid Green 25 (hydrophilic), were compared in three experimental protocols: (1) without liposomes, (2) in the presence of phosphatidylcholine (PC) liposomes, and (3) with wool previously treated with PC liposomes. Physicochemical interactions of liposomes with wool fibers were studied under experimental dyeing conditions with particular interest in the liposome affinity to the fiber surface and changes in the lipid composition of the wool fibers. The results obtained indicate that the presence of liposomes favors the retention of these two dyes in the dyeing bath, this effect being more pronounced in case of the hydrophobic dye. Furthermore, the liposome treatment is accompanied by substantial absorption of PC by wool fibers with simultaneous partial solubilization of their polar lipids (more evident at higher temperatures). This may result in structural modification of the cell membrane complex of wool fibers, which could account for a high level of the dye exhaustion observed at the end of the liposome dyeing process. 相似文献
40.
Determination of selenium, zinc and cadmium in antidandruff shampoos by atomic spectrometry after microwave assisted sample digestion 总被引:1,自引:0,他引:1
Microwave assisted pre-treatments for atomic spectrometric determination (inductive coupled plasma-optical emission spectrometry, ICP-OES or flame atomic absorption spectrometry, FAAS) of metallic elements, usually present in antidandruff shampoos, are proposed. They are based on the digestion of the sample with HNO3 into a closed reactor, which is irradiated at 800 W for a few minutes. Selenium was determined by ICP-OES. The limit of detection was 0.11 mg l−1; the relative standard deviation (R.S.D.) for the selenium content in the samples was in the 0.6–3.6% range. The results obtained were in agreement with the label contents and the recovery of the proposed method was in the 100–106% range. Zinc and cadmium were determined by FAAS. The limit of detection for zinc determination was 0.078 mg l−1; the R.S.D. for zinc contents was in the 0.8–8.6% range. A limit of detection of 0.09 mg l−1 was obtained for cadmium determination; the R.S.D. for cadmium contents was in the 0.7–2.7% range. The determinations were performed after two different sample mineralization pre-treatments — dry ashing (in an electric furnace) and wet mineralization (in a microwave oven). Both methodologies provided comparable results for zinc and cadmium determination in shampoos. The proposed microwave assisted digestion procedures allow a precise and accurate determination of selenium, zinc and cadmium in commercial antidandruff shampoos, and the sample pre-treatment is less time-consuming than the classic methods. 相似文献