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Mixed Micelles (mixed + micelle)
Selected AbstractsDetermination of amino acids by micellar EKC: Recent advances in method development and novel applications to different matricesELECTROPHORESIS, Issue 1 2008Paolo Iadarola Professor Abstract The extensive use of CE for the analysis of amino acids has been well documented in a series of research articles and reviews. Aim of this report is to address the attention of the reader on the recent advances of micellar electrokinetic chromatography for the separation and determination of these analytes. Enhancements in selectivity of this technique through the use of pseudostationary phases containing mixed micelles, polymers, and chiral selectors are presented. Selected applications concerning separation and quantitation of even minute amounts of amino acids in: (i) biological fluids; (ii) microdialysates; (iii) plant cells; (iv) food stuff; and (v) pharmaceutical formulations have also been covered. Advantages of MEKC over other techniques for the amino acid analysis have been underlined. [source] Dietary absorption efficiencies and toxicokinetics of polychlorinated biphenyls in ring doves following exposure to aroclor® mixturesENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 11 2000Ken G. Drouillard Abstract Ring doves (Streptotpelia risoria) were fed a meal of pellets spiked with an Aroclor® mixture. Feces were collected from birds after fasting 31 h postexposure and dietary absorption efficiencies (AbE) of polychlorinated biphenyls (PCBs) were determined by mass balance. Polychlorinated biphenyl AbEs ranged from 0.86 to 0.97 for individual congeners and were similar to the lipid AbE of 0.90. The AbEs exhibited a declining trend with increasing chemical hydrophobicity. The toxicokinetics of PCBs and dietary lipids in blood plasma were also followed in the exposed birds for 25 h after feeding the contaminated meal. Despite decreasing trends in net AbEs with increasing chemical hydrophobicity, all PCBs exhibited similar blood toxicokinetics as observed for dietary lipids. The PCB plasma uptake rate constants exhibited a positive correlation with chemical hydrophobicity such that the most hydrophobic congener PCB 180 approached the plasma uptake rate constant measured for dietary lipids. Trends in assimilation kinetics of PCBs in blood were not consistent with the general prediction that solubility limitations of chemicals in the unstirred water layer (UWL) contribute to declines in net AbEs for highly hydrophobic chemicals. The data are consistent with a micelle-mediated diffusion model, which indicates that dietary lipids and hydrophobic contaminants can cross the UWL and enter intestinal tissues at equivalent rates; however, solubility limitations of highly hydrophobic chemicals in mixed micelles may contribute to decline in net AbEs. [source] Potential MRI Contrast Agents Based on Micellar Incorporation of Amphiphilic Bis(alkylamide) Derivatives of [(Gd,DTPA)(H2O)]2,EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2003Kristof Kimpe Abstract DTPA-bisamide derivatives with alkyl chains containing 14, 16 and 18 carbon atoms were synthesized and complexes of various trivalent lanthanide ions (Ln = Gd, La, Pr, Eu) were formed. Variable temperature proton NMR spectroscopy of paramagnetic praseodymium(III) and europium(III) complexes revealed that long aliphatic substituents considerably increase the energy barrier for the intramolecular rearrangement around the lanthanide ion. The gadolinium(III) complexes were incorporated into mixed micelles, and photon correlation spectroscopy showed that the mean sizes of all the micelles were within the same range. The NMRD curves of all three DTPA-bisamide-gadolinium complexes incorporated in mixed micelles display higher relaxivity values than the commercially available Gd,DTPA contrast agent. The higher relaxivity obtained for the micellar DTPA-bisamide-gadolinium complexes with C14 and C16 chains relative to the micellar DTPA-bisamide-GdIII C18 chain complex could be attributable to the fact that the alkyl chain containing 18 carbon atoms is longer than the alkyl chain of the major component of the micelles, DPPC, in which it is inserted. This would allow increased mobility of the polar head and hence a lower relaxivity. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Effect of self-assemblies of various surfactants in their single and mixed states on the BZ oscillatory reactionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2010Muzaffar Hussain Najar Micelles of different surfactants are well known to affect chemical equilibria and reactivities by selectively sequestering the reagent substrates through electrostatic and hydrophobic interactions. In this article, the effects of micelles of various surfactants on different parameters of the Ce(IV)-catalyzed Belousov,Zhabotinsky (BZ) oscillatory reaction at 35°C in nonstirred closed conditions are studied by employing spectrophotometry and tensiometry. Surfactants used in this study are the cationics hexadecyltrimethylammonium bromide (CTAB) and pentamethylene-1,5-bis(N -hexadecyl- N,N -dimethylammonium)bromide gemini (Gemini), anionic sodium dodecylbenzene sulfonate (SDBS), and nonionic Brij58, whereas the binary surfactant systems used are cationic,nonionic CTAB+Brij58 and anionic,nonionic SDBS+Brij58. The results revealed that the induction period shows a definite variation with increasing concentration of different surfactants above their critical micelle concentration (cmc). The amplitudes of oscillation and absorbance maxima and minima are enhanced in the presence of micelles of CTAB and Gemini surfactants, whereas micelles of SDBS and Brij58 have almost no effect on the nature of the oscillations. However, mixed micelles of CTAB+Brij58 and SDBS+Brij58 binary mixtures show a quite different effect on the overall behavior of the oscillations. The enhanced effect of CTAB and Gemini surfactants on the overall nature of oscillations has been attributed to the positive charge on the surface of their micelles and to some extent on the presence of nitrogen in their head group. The effect of mixed binary micelles may be attributed to their synergistic nature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 659,668, 2010 [source] Synthesis and Bioaccessibility of Fe-Pheophytin Derivatives from Crude Spinach ExtractJOURNAL OF FOOD SCIENCE, Issue 5 2008R.E. Nelson ABSTRACT:, Heme iron is recognized as a highly bioavailable source of iron suitable for treatment of iron deficiency anemia. However, the animal origin of purified heme limits its broad applicability due to religious, personal, and food safety issues. Development of chlorophyll-derived heme mimetics offers opportunities to expand current iron fortification strategies. The objective of this study was the synthesis of Fe-pheophytin (FePhe) derivatives from natural chlorophyll and subsequent evaluation of their digestive behavior and bioaccessibility in vitro. FePhe a and a, were synthesized from crude spinach extracts by treatment with 1.3 M iron(II)chloride and 0.25 M Na-acetate dissolved in glacial acetic acid at 80 °C for 30 min. FePhe-rich extracts (approximately 1 mM) were formulated into corn starch based test meals (7.5% lipid) and subjected to a 2-step in vitro digestion designed to simulate in vivo gastric and small intestinal conditions. Recovery of FePhe following digestion and transfer of FePhe and pheophytins (Phe) from test meal matrix to mixed micelles was assessed by RP C18-HPLC to determine the digestive stability and micellarization efficiency (bioaccessibility). FePhe a and a, derivatives were moderately stable to digestive conditions with recoveries of 52.3% and 58.7%, respectively. Residual Phe a was stable to digestion. Micellarization efficiency of FePhe a (4%) and a, (3.4%) was significantly (P < 0.05) lower than Phe a (25.8%) from test meals. While digestive stability and micellarization efficiency are limiting, the presence of lipophilic FePhe derivatives in mixed micelles suggests that these compounds would be available for subsequent absorption in the intestinal tract. [source] Biorelevant dissolution media: Aggregation of amphiphiles and solubility of estradiolJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 2 2006David Ilardia-Arana Abstract Biorelevant dissolution media containing bile salt and lecithin at concentrations appropriate for fed and fasted state are useful when testing oral solid formulations of poorly water-soluble drugs. Dilution of amphiphile solutions affects the aggregation state of the amphiphiles because bile salt is partitioned between the aqueous phase and the aggregates. The aim of the investigation was to study the effect of dilution on the size distribution of aggregates and its effect on the solubilization capacity. Clear buffered solutions of four intestinal amphiphiles (sodium glycocholate, lecithin, monoolein, and oleic acid) and a combination of these were prepared at high bile salt concentration. Micelles in the glycocholate solutions decreased in size when diluted. The addition of insoluble amphiphiles led to bigger micelles with no clear correlation between size of the micelles and amphiphile concentration. Dilution of the two- and four component media caused enlargement of the mixed micelles and formation of vesicles. The solubility of estradiol in the buffer solution was increased with addition of the amphiphiles. A good correlation (R2,=,0.987) was found between estradiol solubility and mass concentration of the amphiphiles. The results demonstrate that, in the case of estradiol, the concentration of amphiphiles rather than the aggregation state determines the solubilization capacity of the medium. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 95:248,255, 2006 [source] Bilayer to micelle transition of DMPC and alcohol ethoxylate surfactants as studied by isoperibol calorimetryJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2005Leticia Barriocanal Abstract The interaction of dimyristoylphosphatidylcholine (DMPC) with non-ionic surfactants has been studied using isoperibol calorimetry. Phospholipid-surfactant systems were formed in the isoperibol calorimeter with varying amounts of surfactant and the change in enthalpy on formation was measured. Solubilization of the phospholipid lamellae was assessed as a decrease in the enthalpy of reaction of co-films containing DMPC and increasing amounts of three linear alcohol ethoxylate surfactants: C10H21(OCH2CH2)3OH, C10H21(OCH2CH2)5OH, or C12H25(OCH2CH2)7OH. The isoperibol calorimetry data for DMPC/surfactant/water systems were consistent with a theoretical three-stage model for the solubilization of phospholipids by surfactants, whereby phospholipid bilayers are transformed into mixed micelles with increasing amounts of surfactant. The results indicate that: (i) the interaction between phospholipid and surfactants results in a non-linear correlation between the enthalpy of reaction and the surfactant concentration; (ii) the structural stage of the lamellar to micelle transition (mixed bilayers, mixed micelles, or both) can be determined from calorimetric data; (iii) phase boundaries in the solubilization process (bilayer saturation, micelle saturation) can be identified as break points in the enthalpy-concentration curve; and (iv) increasing the hydrophilicity of the surfactant results in a decrease of the surfactant concentration producing the onset of solubilization. © 2005 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:1747,1755, 2005 [source] Micelle-to-vesicle transition induced by oligonucleotide in SDS/DEAB mixed system with a net negative chargeJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2008Xia Guo Abstract Sodium dodecyl sulfate (SDS)/dodecyl triethyl ammonium bromide (DEAB) mixed micelles (with SDS in excess) can transform to vesicles only when the temperature is higher than a critical value. In this study, we report for the first time that oligonucleotide can decrease the critical temperature to a much lower value and, hence, induce micelle-to-vesicle transition. The facilitation efficiency of oligonucleotide on vesicle formation is closely dependent on its size and base composition. Moreover, the SDS/DEAB/oligonucleotide vesicles are negatively charged and the hydrophobic interaction between oligonucleotide and SDS/DEAB mixed micelles is the driving force. As, so far, the report about the facilitation effect of oligonucleotide and DNA on vesicle formation is very limited, this study may provide some helpful information for the application of DNA/amphiphile system. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7491,7504, 2008 [source] Surfactant-Induced Amorphous Aggregation of Tobacco Mosaic Virus Coat Protein: A Physical Methods ApproachMACROMOLECULAR BIOSCIENCE, Issue 2 2008Yuliy V. Panyukov Abstract The interactions of non-ionic surfactant Triton X-100 and the coat protein of tobacco mosaic virus, which is an established model for both ordered and non-ordered protein aggregation, were studied using turbidimetry, differential scanning calorimetry, isothermal titration calorimetry, and dynamic light scattering. It was found that at the critical aggregation concentration (equal to critical micelle concentration) of 138,×,10,6M, Triton X-100 induces partial denaturation of tobacco mosaic virus coat protein molecules followed by protein amorphous aggregation. Protein aggregation has profound ionic strength dependence and proceeds due to hydrophobic sticking of surfactant-protein complexes (start aggregates) with initial radii of 46 nm. It has been suggested that the anionic surfactant sodium dodecyl sulfate forms mixed micelles with Triton X-100 and therefore reverses protein amorphous aggregation with release of protein molecules from the amorphous aggregates. A stoichiometric ratio of 5 was found for Triton X-100-sodium dodecyl sulfate interactions. [source] Highly Ordered Mesoporous Carbonaceous Frameworks from a Template of a Mixed Amphiphilic Triblock-Copolymer System of PEO,PPO,PEO and Reverse PPO,PEO,PPOCHEMISTRY - AN ASIAN JOURNAL, Issue 10 2007Yan Huang Abstract A series of highly ordered mesoporous carbonaceous frameworks with diverse symmetries have been successfully synthesized by using phenolic resols as a carbon precursor and mixed amphiphilic surfactants of poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) (PEO,PPO,PEO) and reverse PPO,PEO,PPO as templates by the strategy of evaporation-induced organic,organic self-assembly (EISA). The transformation of the ordered mesostructures from face-centered (Fdm) to body-centered cubic (Imm), then 2D hexagonal (P6mm), and eventually to cubic bicontinuous (Iad) symmetry has been achieved by simply adjusting the ratio of triblock copolymers to resol precursor and the relative content of PEO,PPO,PEO copolymer F127, as confirmed by small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and nitrogen-sorption measurements. The blends of block copolymers can interact with resol precursors and tend to self-assemble into cross-linking micellar structures during the solvent-evaporation process, which provides a suitable template for the construction of mesostructures. The assembly force comes from the hydrogen-bonding interactions between organic mixed micelles and the resol-precursor matrix. The BET surface area for the mesoporous carbonaceous samples calcined at 600,°C under nitrogen atmosphere is around 600,m2,g,1, and the pore size can be adjusted from 2.8 to 5.4,nm. An understanding of the organic,organic self-assembly behavior in the mixed amphiphilic surfactant system would pave the way for the synthesis of mesoporous materials with controllable structures. [source] | ||||||||||||||||