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Micellar Concentration (micellar + concentration)
Kinds of Micellar Concentration Selected AbstractsInteraction of ostreolysin, a cytolytic protein from the edible mushroom Pleurotus ostreatus, with lipid membranes and modulation by lysophospholipidsFEBS JOURNAL, Issue 6 2003Kristina Sep Ostreolysin is a 16-kDa cytolytic protein specifically expressed in primordia and fruiting bodies of the edible mushroom Pleurotus ostreatus. To understand its interaction with lipid membranes, we compared its effects on mammalian cells, on vesicles prepared with either pure lipids or total lipid extracts, and on dispersions of lysophospholipids or fatty acids. At nanomolar concentrations, the protein lysed human, bovine and sheep erythrocytes by a colloid-osmotic mechanism, compatible with the formation of pores of 4 nm diameter, and was cytotoxic to mammalian tumor cells. A search for lipid inhibitors of hemolysis revealed a strong effect of lysophospholipids and fatty acids, occurring below their critical micellar concentration. This effect was distinct from the capacity of ostreolysin to bind to and permeabilize lipid membranes. In fact, permeabilization of vesicles occurred only when they were prepared with lipids extracted from erythrocytes, and not with lipids extracted from P. ostreatus or pure lipid mixtures, even if lysophospholipids or fatty acids were included. Interaction with lipid vesicles, and their permeabilization, correlated with an increase in the intrinsic fluorescence and ,-helical content of the protein, and with aggregation, which were not detected with lysophospholipids. It appears that either an unknown lipid acceptor or a specific lipid complex is required for binding, aggregation and pore formation. The inhibitory effect of lysophospholipids may reflect a regulatory role for these components on the physiological action of ostreolysin and related proteins during fruiting. [source] Spectral, kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar mediaINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2003N. Ramanathan Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10,3 mol dm,3. At low surfactant concentration (<5 × 10,3 mol dm,3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye,surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (KA) for the formation of dye,SDS complex and the binding constant (KB) for the micellization of dye are determined. Stopped-flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629,636, 2003 [source] The conformation of fusogenic B18 peptide in surfactant solutions,JOURNAL OF PEPTIDE SCIENCE, Issue 4 2008Sandra Rocha Abstract The interaction of B18 peptide with surfactants has been studied by circular dichroism spectroscopy and fluorescence measurements. B18 is the fusogenic motif of the fertilization sea urchin protein. The peptide forms an ,-helix structure when interacting with positively or negatively charged surfactants below and above the critical micellar concentration (CMC). The ,-helix formation is due to binding of surfactant monomers rather than the formation of surfactant micelles on the peptide. Fluorescence measurements show that the CMC of the negatively charged surfactant increases in the presence of B18, supporting the fact that there is a strong interaction between the peptide and monomers. Nonionic surfactant monomers have no effect on the peptide structure, whereas the micelles induce an ,-helical conformation. In this case the helix stabilization results from the formation of surfactant micelles on the peptide. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source] Gd(III)-EPTPAC16, a new self-assembling potential liver MRI contrast agent: in vitro characterization and in vivo animal imaging studies,NMR IN BIOMEDICINE, Issue 4 2008Suzana Torres Abstract The recently reported amphiphilic chelate, [Gd(EPTPAC16)(H2O)]2,, forms supramolecular aggregates in aqueous solution by self-assembly of the monomers with a relaxometrically determined critical micellar concentration (CMC) of 0.34,mM. The effect of sonication on the aggregate size was characterized by dynamic light scattering and relaxometry, indicating the presence of premicellar aggregates and an overall decrease in aggregate size and polydispersity upon sonication, slightly below the CMC. {[153Sm](EPTPAC16)(H2O)}2, radiotracer was evaluated in vivo from , scintigraphy and biodistribution in Wistar rats. It was found to depend strongly on the sample concentration, below or above the CMC, and its sonication, in a way that correlates with the effect of the same factors on the size of the aggregates formed in solution. Below CMC, the very large aggregates of the [153Sm]3+ -labeled chelate were persistently and mainly taken up by the lungs, and also by the macrophage-rich liver and spleen. Sonication of this solution led to loss of the lung uptake. Above CMC, the metal chelate was mainly taken up by the liver, with very little uptake by the spleen and lungs. In vivo, dynamic contrast-enhanced (DCE)-MRI evaluation of the micellar [Gd(EPTPAC16)(H2O)]2, compound in Wistar rats showed a persistent hepatic positive-contrast effect in T1 -weighted images, qualitatively similar to the clinically established GdIII -based hepatobiliary-selective agents. No enhancement effect was observed in the lungs because of the scarcity of mobile protons in this organ, despite the scintigraphic evidence of significant lung retention of the [153Sm]3+ -labeled chelate at concentrations below the CMC. Copyright © 2007 John Wiley & Sons, Ltd. [source] Cancer-associated pH-responsive tetracopolymeric micelles composed of poly(ethylene glycol)- b -poly(L -histidine)- b -poly(L -lactic acid)- b -poly(ethylene glycol)POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 12 2008Kyung Taek Oh Abstract To create a novel vector for specifically delivering anticancer therapy to solid tumors, we used diafiltration to synthesize pH-sensitive polymeric micelles. The micelles, formed from a tetrablock copolymer [poly(ethylene glycol) -b -poly(L -histidine)- b -poly(L -lactic acid)- b -poly(ethylene glycol)] consisted of a hydrophobic poly(L -histidine) (polyHis) and poly(L -lactic acid) (PLA) core and a hydrophilic poly(ethylene glycol) (PEG) shell, in which we encapsulated the model anticancer drug doxorubicin (DOX). The robust micelles exhibited a critical micellar concentration (CMC) of 2.1,3.5,µg/ml and an average size of 65,80,nm pH 7.4. Importantly, they showed a pH-dependent micellar destabilization, due to the concurrent ionization of the polyHis and the rigidity of the PLA in the micellar core. In particular, the molecular weight of PLA block affected the ionization of the micellar core. Depending on the molecular weight of the PLA block, the micelles triggering released DOX at pH 6.8 (i.e. cancer acidic pH) or pH 6.4 (i.e. endosomal pH), making this system a useful tool for specifically treating solid cancers or delivering cytoplasmic cargo in vivo. Copyright © 2008 John Wiley & Sons, Ltd. [source] A rapid method for assessing lipid:protein and detergent:protein ratios in membrane-protein crystallizationACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2003Corrie J. B. DaCosta A simple procedure for rapidly measuring lipid:protein ratios and detergent concentrations at different stages of the solubilization, purification and crystallization of membrane proteins has been developed. Fourier-transform infrared spectra recorded from 10,µl aliquots of solution using a single-bounce diamond-attenuated total reflectance apparatus exhibit characteristic bands arising from the vibrations of lipid, protein and detergent. Lipid:protein molar ratios as low as 5:1 (for a protein with a molecular weight of 300,kDa) are determined by comparing the ratio of the integrated intensity of the lipid ester carbonyl band near 1740,cm,1 with the protein amide I band near 1650,cm,1. Detergent concentrations at levels well below the critical micellar concentration of most detergents are determined by comparing the integrated intensities of the detergent vibrations, particularly in the 1200,1000,cm,1 region, with a standard curve. Protein amide I band-shape analysis provides insight into the effects of detergents on protein secondary structure. The importance of monitoring detergent concentration changes during simple procedures, such as the concentration of a membrane protein by ultrafiltration, is demonstrated. This analytical tool has been used to rapidly establish protocols for minimizing lipid and detergent levels in solubilized membrane-protein samples. [source] Use of a whole-cell biosensor to assess the bioavailability enhancement of aromatic hydrocarbon compounds by nonionic surfactantsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2008Angela Keane Abstract The whole-cell bioluminescent biosensor Pseudomonas putida F1G4 (PpF1G4), which contains a chromosomally-based sep-lux transcriptional fusion, was used as a tool for direct measurement of the bioavailability of hydrophobic organic compounds (HOCs) partitioned into surfactant micelles. The increased bioluminescent response of PpF1G4 in micellar solutions (up to 10 times the critical micellar concentration) of Triton X-100 and Brij 35 indicated higher intracellular concentrations of the test compounds, toluene, naphthalene, and phenanthrene, compared to control systems with no surfactants present. In contrast, Brij 30 caused a decrease in the bioluminescent response to the test compounds in single-solute systems, without adversely affecting cell growth. The decrease in bioluminescent response in the presence of Brij 30 did not occur in the presence of multiple HOCs extracted into the surfactant solutions from crude oil and creosote. The effect of the micellar solutions on the toluene biodegradation rate was consistent with the bioluminescent response in single-solute systems. None of the surfactants were toxic to PpF1G4 at the doses employed in this study, and PpF1G4 did not produce a bioluminescent response to the surfactants nor utilize them as growth substrates. TEM images suggest that the surfactants did not rupture the cell membranes. The results demonstrate that for Pseudomonas putida F1, nonionic surfactants such as Triton X-100 and Brij 35, at doses between 2 and 10 CMC, may increase the bioavailability and direct uptake of micellar phase HOCs that are common pollutants at contaminated sites. Biotechnol. Bioeng. 2008;99: 86,98. © 2007 Wiley Periodicals, Inc. [source] Separation of astaxanthin from cells of Phaffia rhodozyma using colloidal gas aphrons in a flotation columnBIOTECHNOLOGY PROGRESS, Issue 2 2010Maria Dermiki Abstract The aim of this study is to investigate the separation of astaxanthin from the cells of Phaffia rhodozyma using colloidal gas aphrons (CGA), which are surfactant stabilized microbubbles, in a flotation column. It was reported in previous studies that optimum recoveries are achieved at conditions that favor electrostatic interactions. Therefore, in this study, CGA generated from the cationic surfactant hexadecyl trimethyl ammonium bromide (CTAB) were applied to suspensions of cells pretreated with NaOH. The different operation modes (batch or continuous) and the effect of volumetric ratio of CGA to feed, initial concentration of feed, operating height, and flow rate of CGA on the separation of astaxanthin were investigated. The volumetric ratio was found to have a significant effect on the separation of astaxanthin for both batch and continuous experiments. Additionally, the effect of homogenization of the cells on the purity of the recovered fractions was investigated, showing that the homogenization resulted in increased purity. Moreover, different concentrations of surfactant were used for the generation of CGA for the recovery of astaxanthin on batch mode; it was found that recoveries up to 98% could be achieved using CGA generated from a CTAB solution 0.8 mM, which is below the CTAB critical micellar concentration (CMC). These results offer important information for the scale-up of the separation of astaxanthin from the cells of P. rhodozyma using CGA. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 [source] Use of chiral zwitterionic surfactants for enantiomeric resolutions by capillary electrophoresisELECTROPHORESIS, Issue 15 2003Mark R. Hadley Abstract The enantiomeric resolution of 1,1'-binaphthyl-2,2'-diamine and Tröger's base was investigated using the commercially available zwitterionic surfactants 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulphonate (CHAPS) and 3-[(3-cholamidopropyl)dimethylammonio]-2-hydroxy-1-propanesulphonate (CHAPSO). Resolution of the weakly basic chiral probes was achieved using varying concentrations of surfactant, above their critical micellar concentrations, in a phosphate buffer (pH 2.5; 100 mM) to ensure ionisation of the analytes. Both CHAPS and CHAPSO were employed in the absence of additional coselectors or surfactants as sole micellar-forming agents. The addition of organic modifiers, methanol and acetonitrile (ACN), to the background electrolyte (BGE) was found to have a detrimental effect on enantioselectivity presumably by alteration of the phase polarity. [source] Docosahexaenoic acid stabilizes soluble amyloid-, protofibrils and sustains amyloid-,-induced neurotoxicity in vitroFEBS JOURNAL, Issue 4 2007Ann-Sofi Johansson Enrichment of diet and culture media with the polyunsaturated fatty acid docosahexaenoic acid has been found to reduce the amyloid burden in mice and lower amyloid-, (A,) levels in both mice and cultured cells. However, the direct interaction of polyunsaturated fatty acids, such as docosahexaenoic acid, with A,, and their effect on A, aggregation has not been explored in detail. Therefore, we have investigated the effect of docosahexaenoic acid, arachidonic acid and the saturated fatty acid arachidic acid on monomer oligomerization into protofibrils and protofibril fibrillization into fibrils in vitro, using size exclusion chromatography. The polyunsaturated fatty acids docosahexaenoic acid and arachidonic acid at micellar concentrations stabilized soluble A,42 wild-type protofibrils, thereby hindering their conversion to insoluble fibrils. As a consequence, docosahexaenoic acid sustained amyloid-,-induced toxicity in PC12 cells over time, whereas A, without docosahexaenoic acid stabilization resulted in reduced toxicity, as A, formed fibrils. Arachidic acid had no effect on A, aggregation, and neither of the fatty acids had any protofibril-stabilizing effect on A,42 harboring the Arctic mutation (A,E22G). Consequently, A,Arctic-induced toxicity could not be sustained using docosahexaenoic acid. These results provide new insights into the toxicity of different A, aggregates and how endogenous lipids can affect A, aggregation. [source] | |||||||||||||