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81.
María del Mar Graciani Amalia Rodríguez María Mu?oz María Luisa Moyá 《Reaction Kinetics and Catalysis Letters》2003,78(1):113-119
The 1-chloro-2,4-dinitrobenzene + OH- reaction was studied in tetradecyltrimethylammonium bromide aqueous micellar solutions. Influence of changes in [surfactant]
as well as in [NaOH] on the observed rate constant were rationalized by using pseudophase kinetic models. At high hydroxide
ions concentration an additional pathway across the micellar boundary had to be considered.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
82.
The spontaneous hydrolysis of phenyl chloroformate was studied in various anionic, nonionic, zwitterionic, and cationic aqueous micellar solutions, as well as in mixed anionic–nonionic micellar solutions. In all cases, an increase in the surfactant concentration results in a decrease in the reaction rate and micellar effects were quantitatively explained in terms of distribution of the substrate between water and micelles and the first‐order rate constants in the aqueous and micellar pseudophases. A comparison of the kinetic data in nonionic micellar solutions to those in anionic and zwiterionic micellar solutions makes clear that charge effects of micelles is not the only factor responsible for the variations in the reaction rate. Depletion of water in the interfacial region and its different characteristics as compared to bulk water, the presence of high ionic concentration in the Stern layer of ionic micelles, and differences in the stabilization of the initial state and the transition state by hydrophobic interactions with surfactant tails can also influence reactivity. The different deceleration of the reaction observed in the various micellar solutions studied was discussed by considering these factors. Synergism in mixed‐micellar solutions is shown through the kinetic data obtained in these media. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 445–451, 2002 相似文献
83.
Bruno Crociani Francesca Dibianca Amalia Giovenco Alberto Scrivanti 《Journal of organometallic chemistry》1985,291(2):259-272
The oxidative addition of 2-chloropyrimidine or 2-chloropyrazine to [Pd(PPh3)4] yields a mixture of trans-[PdCl(C4H3N2-C2)(PPh3)2] (I) and [PdCl(μ-C4H3N2-C2,N1)(PPh3 (II) (C4H3N2 = 2-pyrimidyl or 2-pyrazyl group). The mononuclear complexes I are quantitatively converted into the binuclear species II upon treatment with H2O2. The reaction of II with HCl gives the N-monoprotonated derivatives cis-[PdCl2(C4H4N2-C2)(PPh3)] (III), from which the cationic complexes trans-[PdCl(C4H4N2-C2)(L) (L = PPh3, IV; PMe2Ph, V; PEt3, VI) can be prepared by ligand substitution reactions. Reversible proton dissociation occurs in solution for III–VI. The low-temperature 1H NMR spectra of trans-[PdCl(C4H4N2-C2)(PMe2Ph)2]ClO4 show that the heterocyclic moiety undergoes restricted rotation around the PdC2 bond and that the 2-pyrazyl group is protonated predominantly at the N1 atom. These results and the 13C NMR data for the PEt3 derivatives are interpreted on the basis of a significant dπ → π★ back-bonding contribution to the palladium—carbon bond of the protonated ligands. 相似文献
84.
Decanoic acid reverse micelle-based coacervates for the microextraction of bisphenol A from canned vegetables and fruits 总被引:1,自引:0,他引:1
Decanoic acid reverse micelle-based coacervates were proposed for the extraction of bisphenol A (BPA) from canned vegetables and fruits prior to its determination by liquid chromatography and fluorescence detection at lambda(exc) = 276 nm and lambda(em) = 306 nm. The procedure involved the extraction of minute quantities (300-700 mg) of homogenized food sample with an aqueous solution containing 10% of THF and 0.5% of decanoic acid, conditions under which the coacervate (around 340 microL) formed in situ and instantaneously. The overall sample treatment, which included extraction and centrifugation, took about 25-30 min, and several samples could be simultaneously treated using conventional lab equipment. No clean-up or solvent evaporation were required. Extraction efficiencies mainly depended on the decanoic acid and THF concentration in the aqueous solution and were not affected by the pH or the temperature in the ranges studied (1-4 and 20-60 degrees C, respectively). Recoveries in samples ranged between about 81 and 96%. The precision of the method, expressed as relative standard deviation, was about 3% and the quantitation limit was around 9 ng g(-1), which was far below the current specific migration limit (SML) set for BPA by the EU Commission (600 ng g(-1)). The method was successfully applied to the determination of BPA in the solid content of canned fruit salad, peaches in syrup, mango slices, red peppers, sweetcorn, green beans and peas. BPA was present at concentrations in the range from 7.8 to 24.4 ng g(-1) in canned fruits and from 55 to 103 ng g(-1) in canned vegetables. 相似文献
85.
Time‐Dependent Free‐Particle Salpeter Equation: Numerical and Asymptotic Analysis in the Light of the Fundamental Solution 下载免费PDF全文
A detailed study of the spinless (1+1)D free‐particle Salpeter equation is presented. It involves several aspects of the topic: from the analysis of the behavior of solutions of the equation, both numerically evaluated and asymptotically approximated for definite initial conditions, to the comparison with the behavior of the corresponding solutions of the Schrödinger equation in order to both highlight the differences and to possibly understand how the latter “flow” in the former. Interesting analogies with other fields of physics, in particular with optics, are suggested. 相似文献
86.
87.
Marcelino Anguiano-Morales Amalia Martínez Sabino Chávez-Cerda 《Optics Communications》2008,281(3):401-407
A combination of an axicon and an amplitude mask is used to obtain an intensity distribution that differs from the typical Bessel one. Experimental and numerical characterization of the field is made for different propagation distances and types of amplitude masks. 相似文献
88.
R Domínguez A Rodríguez A Maestre I Robina ML Moyá 《Journal of colloid and interface science》2012,386(1):228-239
In this work, three didodecyl dicationic dibromide dimeric surfactants 12-s-12,2Br(-), with different methylene spacer lengths (s=7, 9, and 11) were prepared and characterized and their properties compared to those of 12-s-12,2Br(-) surfactants with s=2, 3, 4, 5, 6, 8, 10, and 12. Information about the critical micelle concentration, the micellar ionization degree, the average aggregation number and the polarity of the interfacial region, and microviscosity of the micellar interior was obtained by using different techniques. Their surface activity was investigated by means of surface tension measurements. Micellization was also studied by using (1)H NMR and diffusion NMR (DOSY) spectroscopy as well as isothermal titration calorimetry. The values of the thermodynamic parameters show that the dimeric surfactants micellization is exothermic and driven by entropy. The occurrence of morphological transitions upon increasing surfactant concentration was studied, and the results indicate that the spacer length, s, plays a key role in the micellar growth of 12-s-12,2Br(-) aggregates. The value of s not only control the magnitude of C(*), the surfactant concentration above which the morphological transition from spherical micelles into elongated ones occurs, but also the sign of the enthalpy change accompanying the sphere-to-rod transition. 相似文献
89.
Martín VI Rodríguez A del Mar Graciani M Moyá ML 《Journal of colloid and interface science》2012,368(1):326-335
The micellization and micellar growth in the mixtures of N,N-dimethyl, N-phenyl,N-dodecylammonium bromide, PH12, N,N-dimethyl,N-ciclohexylmethyl,N-dodecylammonium bromide, CH12, and their two dimeric counterparts m-dimethylphenyl-α-ω-bis(dodecyldimethylammonium) bromide, 12PH12, and m-dimethylciclohexyl-α-ω-bis(dodecyldimethylammonium) bromide, 12CH12, with dodecyltrimethylammoniumbromide, DTAB, and with N-decanoyl N-methylglucamide, MEGA10, were investigated at 303 K. Circular dichroism, CD, experiments showed the formation of mixed micelles. Two-dimensional, 2D, rotating frame nuclear Overhauser effect spectroscopy (ROESY) experiments indicated that the arrangement of the rings in the pure and mixed micelles is similar, with the rings bent into the micelle interior avoiding contact with water. Application of different theoretical approaches shows that PH12 and CH12 mixtures with DTAB and with MEGA10 behave almost ideally. The binary systems of 12PH12 and 12CH12 with DTAB and with MEGA10 show a non-ideal behavior. An increment in the solution mole fraction of MEGA10 and DTAB diminishes the tendency of the micellar aggregates to grow. 相似文献
90.
Miguel ángel García-Sevillano Macarena González-Fernández Rocío Jara-Biedma Tamara García-Barrera Amalia Vioque-Fernández Juan López-Barea Carmen Pueyo José Luis Gómez-Ariza 《Chemical Papers》2012,66(10):914-924
A speciation approach based on orthogonal chromatographic systems coupled to inductively coupled plasma mass spectrometry (ICP-MS) was used to characterise the biological response of free-living mice Mus spretus to environmental pollution caused by arsenic in different areas of the Do?ana National Park (south-west Spain). The relative presence of inorganic and organic forms of arsenic was studied in cytosolic extracts from high metabolic activity organs of Mus spretus mice: kidneys, liver, and brain. An instrumental coupling of size-exclusion chromatography with UV and collision/reaction cell-ICP-MS detectors (SEC-UV-ICP-ORC-MS) both in analytical and preparative scale was used for this purpose. The results showed the presence of low molecular mass (LMM) molecules linked to arsenic in these tissues especially in the kidneys, where the presence of these arsenic metabolites was higher. On the other hand, the presence of these arsenicals varied from one area to the other, which can be related to a different occurrence of contaminants. These low molecular mass fractions were collected by preparative SEC chromatography for later study with ion exchange chromatography and detection by ICP-ORC-MS, using both anionic and cationic columns. The results showed the higher presence of MMA and DMA in kidneys of mice caught in contaminated areas and the existence of small amounts of unidentified arsenicals when cation-exchange chromatography was used, which could be related to the presence of dimethylarsinoylethanol (DMAE), thioarsenic species, or arsenocholine (AsC). 相似文献