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141.
Solà Vázquez A Martín A Costa-Fernandez JM Ruiz Encinar J Bordel N Pereiro R Sanz-Medel A 《Analytical and bioanalytical chemistry》2007,389(3):683-690
There is an increasing concern regarding the toxicity and environmental distribution and impact of brominated organic compounds
employed as flame retardants. Thus, present interest in searching for new analytical techniques and methods allowing a rapid,
simple and reliable detection of those compounds in materials and wastes potentially containing such flame retardants is not
surprising. The feasibility of using radiofrequency glow discharge plasma spectrometry coupled with optical emission spectrometry
(rf-GD-OES) as a rapid and simple tool to directly analyse bromine-containing flame-retardant polymeric layers is investigated
here. Polymeric layers for calibration were made by mixing appropriate amounts of tetrabromobisphenol A, bisphenol A, phloroglucinol
and diphenylmethane-4,4′-diisocyanate in tetrahydrofuran. The corresponding blanks (polymers without tetrabromobisphenol A)
were also prepared. Detection of bromine was investigated both in the visible (at 470.48 nm) and in the near-infrared (at
827.24 nm) regions, using a charge-coupled device for detection. Discharge parameters affecting the emission intensity of
bromine were first optimized (in argon and helium as possible plasma gases) and the analytical performance characteristics
were then evaluated. The best detection limit (0.044% Br) was achieved measuring Br I 827.24 nm in a He discharge, using a
forward power of 70 W and a pressure of 45 Torr. The linearity range extended up to 27% Br. Finally, the applicability of
the rf-GD-OES method proposed to the quantitative analysis of bromine in solid materials coated with flame-retardant commercial
paints was successfully demonstrated.
Figure Flame Retardants 相似文献
142.
143.
Olivier C Grote Z Solari E Scopelliti R Severin K 《Chemical communications (Cambridge, England)》2007,(39):4000-4002
The reaction of [(benzene)RuCl(2)](2) with a piperazine-bridged bis(dihydroxypyridine) ligand and LiOH leads to the formation of an expanded helicate, which is able to bind phosphate and acetate in aqueous solution at neutral pH. 相似文献
144.
Fernández-López JA Castellar R Obón JM Almela L 《Journal of chromatographic science》2007,45(3):120-125
The influence of pH and moderate heating (50 degrees C) on the color and individual betacyanin content of pigment extracts from cactus pear fruits (Opuntia stricta) is studied in the course of this paper. The study is carried out by using a high-performance liquid chromatograph equipped with a photodiode array detector and coupled to a mass spectrometer. The results point to a pH-dependent degradation mechanism, which is reflected in the chromatographic patterns obtained at different exposure times (0-28 h). At pH 3, 15-descarboxy-betanin is the most resistant betacyanin derivative. At pH 5, seven peaks are detected after 8 h, the most prominent being betanin, cyclo-dopa-5-O-beta-glucoside, and betalamic. In the assay conducted at pH 7, rapid color loss affects all the pigments, except for betanin. 相似文献
145.
A new synthetic strategy for the construction of boron-based macrocycles and dendrimers is described. Condensation of aryl- and alkylboronic acids with 3,4-dihydroxypyridine is shown to give pentameric macrocycles in which five boronate esters are connected by dative B-N bonds. Three macrocycles have been characterized crystallographically. The boron atoms of these assemblies represent chiral centers, and the assembly process is highly diastereoselective. Attachment of amino or aldehyde groups in the meta position of the arylboronic acid building blocks does not interfere with macrocyclization. This allows performing multicomponent assembly reactions between functionalized boronic acids, dihydroxypyridine ligands, and amines or aldehydes, respectively. Reaction of 3,5-diformylphenylboronic acid, 3,4-dihydroxypyridine, and a primary amine R-NH2 (R=Ph, Bn) gives dendritic nanostructures having a pentameric macrocyclic core and 10 amine-derived R groups in their periphery. Combination of 3,5-diformylphenylboronic acid with 2,3-dihydroxypyridine and the dendron 3,5-(benzyloxy)benzylamine, on the other hand, results in formation of a dendrimer with a tetrameric macrocyclic core and eight dendrons in its periphery. 相似文献
146.
Fernández MC Sánchez CC Rodríguez Niño MR Rodríguez Patino JM 《Langmuir : the ACS journal of surfaces and colloids》2007,23(13):7178-7188
In this work we have analyzed the structural, topographical, and shear characteristics of mixed monolayers formed by adsorbed beta-lactoglobulin (beta-lg) and spread monoglyceride (monopalmitin or monoolein) on a previously adsorbed protein film. Measurements of the surface pressure (pi)-area (A) isotherm, Brewster angle microscopy (BAM), and surface shear characteristics were obtained at 20 degrees C and at pH 7 in a modified Wilhelmy-type film balance. The pi-A isotherm and BAM images deduced for adsorbed beta-lactoglobulin-monoglyceride mixed films at pi lower than the equilibrium surface pressure of beta-lactoglobulin (pi(e)(beta-lg)) indicate that beta-lactoglobulin and monoglyceride coexist at the interface. However, the interactions between protein and monoglyceride are somewhat weak. At higher surface pressures (at pi > or = pi(e)(beta-lg)) a protein displacement by the monoglyceride from the interface takes place. The surface shear viscosity (eta(s)) of mixed films is very sensitive to protein-monoglyceride interactions and displacement as a function of monolayer composition (protein/monoglyceride fraction) and surface pressure. Shear can induce change in the morphology of monoglyceride and beta-lactoglobulin domains, on the one hand, and segregation between domains of the film-forming components on the other hand. In addition, the displacement of beta-lactoglobulin by the monoglycerides is facilitated under shear conditions. 相似文献
147.
Giovanni Maglio Giuseppe Nese Margherita Nuzzo Rosario Palumbo 《Macromolecular rapid communications》2004,25(12):1139-1144
Summary: Star‐shaped hydroxy‐terminated poly(ε‐caprolactone)s (ssPCL), with arms of different lengths, were obtained by ring‐opening polymerization (ROP) of ε‐caprolactone initiated by pentaerythritol, and were condensed with α‐methyl‐ω‐(3‐carboxypropionyloxy)‐poly(ethylene oxide)s ( = 550–5 000) to afford four‐armed PCL‐PEO star diblock copolymers (ssPCL‐PEO). The polymers were characterized by 1H and 13C NMR spectroscopy and size‐exclusion chromatography (SEC). The melting behavior of ssPCLs was studied by differential scanning calorimetry (DSC). X‐ray diffraction and DSC techniques were used to investigate the crystalline phases of ssPCL‐PEOs.
148.
Ma Rosario Rodrguez Nio Cecilio Carrera Snchez Juan M.Rodrguez Patino 《Colloids and surfaces. B, Biointerfaces》1999,12(3-6):161-173
Casein is well known to be a good protein emulsifier and β-casein is the major component of casein and commercial sodium caseinate. This work studies the behaviour of β-casein at the interface. The interfacial characteristics (structure and stability) of β-casein spread films have been examined at the air–water interface in a Langmuir-type film balance, as a function of temperature (5–40°C) and aqueous phase pH (pH 5 and 7). From surface pressure–area isotherms (π–A isotherms) as a function of temperature we can draw a phase diagram. β-Casein spread films present two structures and the collapse phase. That is, there is a critical surface pressure and a surface concentration at which the film properties change significantly. This transition depends on the temperature and the aqueous phase pH. The film structure was observed to be more condensed and β-casein interfacial density was higher at pH 5. β-Casein films were stable at surface pressures lower than equilibrium surface pressure. In fact, no hysteresis was observed in π–A isotherms after continuous compression-expansion cycles or over time. The relative area relaxation at constant surface pressure (10 or 20 mN m−1) and the surface pressure relaxation at constant area near the monolayer collapse, can be fitted by two exponential equations. The characteristic relaxation times in β-casein films can be associated with conformation–organization changes, hydrophilic group hydration and/or surface rheology, as a function of pH. 相似文献
149.
Assuming that the mechanism proposed byGell-Mann and Hartle works as a mechanism fordecoherence and classicalization of the metric field, weformally derive the form of an effective theory for thegravitational field in a semiclassical regime. This effectivetheory takes the form of the usual semiclassical theoryof gravity, based on the semiclassical Einsteinequation, plus a stochastic correction which accounts for the backreaction of the lowest order matterstress-energy fluctuations. 相似文献
150.
Rosario Benavente Ernesto Prez Raúl Quijada 《Journal of Polymer Science.Polymer Physics》2001,39(3):277-285
Stress–strain and microhardness measurements were carried out on a series of copolymers of ethylene and 1‐octadecene with different comonomer contents in the corresponding homopolymer of ethylene, synthesized with a metallocene catalyst. The different mechanical properties, deduced from the stress–strain curves (Young's modulus, yield stress, deformation at break, and energy to break) are interpreted in terms of the crystallinity and molecular weight of the samples because these two characteristics show considerable variations with the comonomer content. The microhardness values are explained in terms of these properties, and they are also correlated with Young's moduli and yield stresses deduced from the stress–strain curves. Linear relations are found between microhardness and yield stress and between the logarithm of the microhardness and the logarithm of the elastic modulus. The properties deduced from these lines are compared with literature values. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 277–285, 2001 相似文献