SEARCH · PubMed Health

Results for “Phase Separation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,171 records · Page 65Linked to original sources

PubMed2002

Theoretical and finite-element investigation of the mechanical response of spinodal structures.

In recent years there have been major advances in our understanding of the mechanisms of phase separation in polymer and copolymer blends, to the extent that good control of phase-separated morphology is a real possibility. Many groups are studying the computational simulation of polymer phase separation. In the light of this, we are exploring methods which will give insight into the mechanical response of multiphase polymers. We present preliminary results from a process which allows the production of a two-dimensional finite-element mesh from the contouring of simulated composition data. We examine the stretching of two-phase structures obtained from a simulation of linear Cahn-Hilliard spinodal phase separation. In the simulations, we assume one phase to be hard, and the other soft, such that the shear modulus ratio G is large (>or= 10(3)). We indicate the effect of varying composition on the material modulus and on the distribution of strains through the stretched material. We also examine in some detail the symmetric structures obtained at 50% composition, in which both phases are at a percolation threshold. Inspired by simulation results for the deformation of these structures, we construct a "scaling" theory, which reproduces the main features of the deformation. Of particular interest is the emergence of a lengthscale, below which the deformation is non-affine. This length is proportional to G(1/4), and hence is still quite small for all reasonable values of this ratio. The same theory predicts that the effective composite modulus scales also as G(1/4), , which is supported by the simulations.

Journal Article↗

PubMed2006

Metolose-PEG interaction as seen by positron annihilation spectroscopy.

The plasticizing effects of poly(ethylene glycol) (PEG 400) on methylcellulose (Metolose) cast films were studied by conventional physicochemical methods and positron annihilation spectroscopy. The PEG concentrations relative to the total polymer content were varied within the range 0-75% (w/w). At low concentrations (below 33.3%, w/w), the plasticizer was found to build in into the methylcellulose structure. On the other hand, at higher concentrations (above 50%, w/w), it formed small separate phases in the films. Positron annihilation spectroscopy (PALS) was applied to track the Metolose-PEG interaction. Controlled ageing of Metolose-PEG films at room temperature and at 75% RH revealed a significant difference between the ageing processes of the monophase and those of the separate phase films. The ageing involves two steps in both cases: a fast and a slow one. The PALS measurements demonstrated that the slow process is hindered in the phase-separated samples.

Elasticity↗

PubMed2005

Quantification of glycosaminoglycans by reversed-phase HPLC separation of fluorescent isoindole derivatives.

Glycosaminoglycans (GAGs) are linear polysaccharides made by all animal cells. GAGs bind to hundreds of proteins, such as growth factors, cytokines, chemokines, extracellular matrix components, protease inhibitors, proteases, and lipoprotein lipase, through carbohydrate and protein interactions. These interactions control many multicellular processes. The increased use of GAGs isolated from cells and small tissue samples in bioassays and binding experiments demands a sensitive and robust quantification method. We have developed such a method, which is based on a popular assay for amino acid analysis. We have refined it to enhance GAG quantification. It allows the quantification of glucosamine- and galactosamine-containing GAGs after the reversed-phase separation of their fluorescent isoindole derivatives. The derivatives are created by the reaction of o-phthaldialdehyde and 3-mercaptopropionic acid (3MPA) with the amino group of hexosaminitol monosaccharides generated from GAG acid hydrolysis and sodium borohydride reduction. The advantages of our method include automatic derivitization, a simple chromatograph with clean separation of glucosaminitol and galactosaminitol derivatives from contaminating amino acids, excellent sensitivity with 0.04 pmol detection, and linearity from 2.5 to 1280 pmol. A major advantage is that it can be readily implemented in any laboratory with typical reversed-phase high performance liquid chromatography (HPLC) equipment.

3-Mercaptopropionic Acid↗

PubMed1998

Effects of nonlamellar-prone lipids on the ATPase activity of SecA bound to model membranes.

The effect of nonlamellar-prone lipids, diacylglycerol (DG) and phosphatidylethanolamine (PE), on the ATPase activity of SecA was examined. When Escherichia coli PE of the standard vesicles composed of 60 mol% of this lipid and 40 mol% of dioleoylphosphatidylglycerol (DOPG) is gradually replaced with either dioleoylglycerol (DOG) or dioeloyl PE (DOPE), the ATPase activity of SecA present together increased appreciably. On the other hand, when E. coli PE of the standard vesicles was replaced with DOG analogs, the SecA ATPase activity decreased slightly, and when replaced with phosphatidylcholine the decrease in the ATPase activity was more appreciable. When DOPE or E. coli PE was added to PC vesicles, the SecA ATPase activity was enhanced only slightly, suggesting that the hexagonal II structure per se is not important for the ATPase activity increase. It was observed that DOG induced phase separation of PG, and the lamellar-hexagonal II (L-HII) transition temperature of vesicles decreased by about 10 degreesC. The DOG analogs had no effect on these properties, suggesting the importance of the phase separation of PG and the decrease of L-HII transition temperature of lipid bilayers to the SecA ATPase activity. The phase separation of PG by Ca2+ also brought about increased ATPase activity of SecA, underlining the importance of phase separation of PG for the enzyme activity. The incorporation of DOG or DOPE in the vesicle also increased the amount of SecA bound to model membranes and the extent of SecA penetration into the membrane. Studies with vesicles without SecA showed increased exposure of hydrophobic acyl chains when the DOG was present. Taken together, these observations suggest that the phase separation of PG and/or the bilayer penetration of SecA are mainly responsible for the enhanced SecA-vesicle interaction with concomitant increase in SecA ATPase activity.

Adenosine Triphosphatases↗

PubMed2006

Strategies for interfacing solid-phase microextraction with liquid chromatography.

Solid-phase microextraction (SPME) techniques are equally applicable to both volatile and non-volatile analytes, but the progress in applications to gas-phase separations has outpaced that of liquid-phase separations. The interfacing of SPME to gas chromatographic equipment has been straight-forward, requiring little modification of existing equipment. The requirement of solvent desorption for non-volatile or thermally labile analytes has, however, proven challenging for interfacing SPME with liquid-phase separations. Numerous options to achieve this have been described in the literature over the past decade, with applications in several different areas of analysis. To date, no single strategy or interface device design has proven optimal. During method development analysts must select the most appropriate interfacing technique among the options available. Out of these options three general strategies have emerged: (1) use of a manual injection interface tee; (2) in-tube SPME; and (3) off-line desorption followed by conventional liquid injection. In addition, there has been interest in coupling SPME directly to electrospray ionisation and matrix-assisted laser desorption ionisation (MALDI) for mass spectrometry. Several examples of each of these strategies are reviewed here, and an overview of their use and application is presented.

Chromatography, High Pressure Liquid↗

PubMed1992

Spontaneous domain formation of phospholipase A2 at interfaces: fluorescence microscopy of the interaction of phospholipase A2 with mixed monolayers of lecithin, lysolecithin and fatty acid.

Fluorescence microscopy has recently been proven to be an ideal tool to investigate the specific interaction of phospholipase A2 with oriented substrate monolayers. Using a dual labeling technique, it could be shown that phospholipase A2 can specifically attack and hydrolyze solid analogous L-alpha-DPPC domains. After a critical extent of monolayer hydrolysis the enzyme itself starts to aggregate forming regular shaped protein domains (Grainger et al. (1990) Biochim. Biophys. Acta 1023, 365-379). In order to confirm that the existence of hydrolysis products in the monolayer is necessary for the observed aggregation of phospholipase A2, mixed monolayers of D- and L-alpha-DPPC, L-alpha-lysoPPC and palmitic acid in different ratios were examined. The phase behavior and the interaction of these films with phospholipase A2 were directly visualized with an epifluorescence microscope. Above a certain critical concentration of lysolecithin and palmitic acid in the monolayer, compression of these mixed films leads to phase separation and formation of mixed domains of unknown composition. Their high negative charge density is evidenced by preferential binding of a cationic dye to these phase-separated areas. Introduction of fluorescence-labeled phospholipase A2 underneath these mixed domains results in rapid binding of the protein to the domains without visible hydrolytic activity, regardless of whether the L-form or the D-form of the DPPC were used. In binary mixtures, only those with DPPC/palmitic acid show formation of phase-separated areas which can be specifically targeted by phospholipase A2 leading to a rapid formation (within 2 min) of protein domains. Experiments with pyrenedecanoic acid containing monolayers give the first direct evidence that acid is located above the enzyme domains. These results show that a locally high negative charge density of the phase-separated domains is one of the prerequisites for the binding of phospholipase A2. In addition, however, small amounts of D- or L-alpha-DPPC headgroups within the domains of the monolayer seem to be necessary for recognition followed by fast binding of the protein to the domains. This is confirmed by experiments with mixed monolayers of diacetylene carboxylic acid and D-alpha-DPPC. The acid--immiscible with lecithin--forms well defined pure acid domains in the monolayer. While the cationic dye can be docked rapidly to these phase separated areas, no preferential enzyme binding and thus no protein domain formation below these acid domains can be induced.

1,2-Dipalmitoylphosphatidylcholine↗

PubMed2000

Compositions and phase diagrams for aqueous systems based on proteins and polysaccharides.

Limited thermodynamic compatibility of proteins with other proteins and proteins with polysaccharides is a fundamental phenomenon that has been demonstrated in more than 200 biopolymer pairs. These systems can undergo a liquid-liquid phase separation resulting in the different macromolecular components primarily concentrated in the different phases. This occurs under conditions (pH values and ionic strengths) inhibiting attraction between nonidentical biopolymers, i.e., the formation of interbiopolymer complexes. Generally, phase separation takes place when the total concentration of the macromolecular components exceeds a certain critical value. The excluded volume of the macromolecules determines both their thermodynamic activity and phase separation threshold. Phase diagrams of biopolymer mixtures and physicochemical features of biphasic systems are considered here. Attention is centered on the limited compatibility of the main classes of proteins and various polysaccharides and on the effects of variables such as pH, ionic strength, temperature and shear forces on the phase state, equilibrium and structure of these two-phase liquid systems. The general nature of the phenomenon of thermodynamic incompatibility of biopolymers accounts for its importance in structure formation in cytoplasm.

Animals↗

PubMed2003

Effect of synthesis temperature of PEO-grafted PU/PS IPNs on surface morphology and in vitro blood compatibility.

When hydrophilic/hydrophobic polymers have a microdomain structure, platelet adhesion and activation are effectively suppressed by prohibition of the excessive assembly of glycoproteins and adenosine triphosphate (ATP) consumption of the platelets on the surface. In this study, poly(ethylene oxide)-grafted hydrophilic polyurethane (PU)/hydrophobic polystyrene (PS) interpenetrating polymer networks (IPNs) were synthesized by varying the synthesis temperature to control the phase separation and the microdomain surface structure, and the effect of the degree of phase separation on the in vitro blood compatibility. The size of the dispersed PS-rich domains in the PU-rich matrix decreased, and the hydrophilicity also decreased as the synthesis temperature of the PS network during the IPN synthesis was decreased, as the phase separation was suppressed during the synthesis. The amount of the adsorbed bovine plasma fibrinogens (BPF) on the PEO-grafted PU/PS IPNs decreased as the synthesis temperature was decreased, and the in vitro adhesion of the platelets was also suppressed on the PEO-grafted PU/PS IPNs prepared at lower temperature. The microdomain structure on the surface affected the adhesion and the activation of the adhered platelets, and the suppression of the phase separation resulted in the decrease of the domain size, which also enhanced the blood compatibility of the PEO-grafted PU/PS IPNs.

Animals↗

PubMed1992

Effects of temperature on the phase behavior and permeability of thylakoid lipid vesicles : relevance to chilling stress.

Large unilamellar vesicles composed of thylakoid glycolipids, phosphatidylglycerol, and varying proportions of dipalmitoylphosphatidylglycerol (DPPG) have been examined for the temperature dependence of their permeability to (86)Rb(+) and for the occurrence of liquid-crystalline to gel (L(alpha)-to-L(beta)) phase separations. In vesicles in which the normal 12 mole percent of moderately unsaturated thylakoid phosphatidylglycerol was partially or completely replaced by DPPG, analysis by differential scanning calorimetry indicated that an L(alpha)-to-L(beta) phase separation did not occur between 0 and 60 degrees C. However, in similar vesicle dispersions that were first subjected to a freeze-thaw cycle, L(alpha)-to-L(beta) phase separations were observed to occur between 17 and 53 degrees C. The temperature and enthalpy of these phase separations were closely related to the proportion of DPPG in the original lipid mixture. In parallel experiments, large unilamellar vesicles were measured for their permeability to (86)Rb(+) between 7 and 30 degrees C. There were no systematic increases in permeability to (86)Rb(+) as a function of DPPG content at the temperatures relevant to chilling stress in higher plants. It is concluded that (a) L(alpha)-to-L(beta) phase separations do not occur in well-defined galactolipid vesicles containing </=12 mole percent DPPG between 0 and 60 degrees C and (b) these vesicles show no alterations in permeability to (86)Rb(+) between 7 and 30 degrees C that are relevant to chilling stress in higher plants.

Journal Article↗

PubMed2004

Modulation of the phase heterogeneity of aminoglycerophospholipid mixtures by sphingomyelin and monovalent cations: maintenance of the lamellar arrangement in the biological membranes.

The phase behaviour of mixed molecular species of phosphatidylethanolamine, phosphatidylserine and sphingomyelin of biological origin were examined in aqueous co-dispersions using synchrotron X-ray diffraction. The co-dispersions of phospholipids studied were aimed to model the mixing of lipids populating the cytoplasmic and outer leaflets in the resting or "scrambled" activated cell membrane. Mixtures enriched with phosphatidylethanolamine and phosphatidylserine were characterized by a phase separation of non-lamellar phases (cubic and inverted hexagonal) with a lamellar gel phase comprising the most saturated molecular species. Inclusion of sphingomyelin in the mixture resulted in a suppression of the hexagonal-II phase in favour of lamellar phases at temperatures where a proportion of the phospholipid was fluid. The effect was also dependent on the total amount of sphingomyelin in ternary mixtures, and the lamellar phase dominated in mixtures containing more than 30 mol%, irrespective of the relative proportions of phosphatidylserine/sphingomyelin. A transition from gel to liquid-crystal phase was detected by wide-angle scattering during heating scans of ternary mixtures enriched in sphingomyelin and was shown by thermal cycling experiments to be coupled with a hexagonal-II phase to lamellar transition. In such samples there was evidence of a coexistence of non-lamellar phases with a lamellar gel phase. A transition of the gel phase to the fluid state on heating from 35 to 41 degrees C was evidenced by a progressive increase in the lamellar d-spacing. The presence of calcium enhanced the phase separation of a lamellar gel phase from a hexagonal-II phase in mixtures enriched in phosphatidylserine. This effect was counteracted by charge screening with 150 mM NaCl. The effect of sphingomyelin on stabilizing the lamellar phase is discussed in the context of an altered composition in the cytoplasmic/outer leaflets of the plasma membrane resulting from scrambling of the phospholipid distribution. The results suggest that a lamellar structure can be retained by the inward translocation of sphingomyelin in biological membranes. The presence of monovalent cations serves also to stabilize the bilayer in activated cells where a translocation of aminoglycerophospholipids and an influx of calcium occur simultaneously.

Amines↗

PubMed2002

Modulation of hyaluronan in the migratory pathway of mouse primordial germ cells.

In the present report we followed the distribution of hyaluronan during the phases of separation, migration, and colonization of the primordial germ cell migratory process. Hyaluronan was detected by the use of two cytochemical methods: (1) ruthenium hexammine trichloride (RHT) associated with enzymatic treatment with hyaluronate lyase and (2) a binding specific probe for hyaluronan. After RHT treatment the proteoglycans and/or glycosaminoglycans were observed as a meshwork formed by electron-dense granules connected by thin filaments. After enzymatic digestion, no filaments could be detected in the migratory pathway. Quantitative analysis showed a close correlation between cell migration and the concentration of RHT-positive filaments. It was also shown that high amounts of hyaluronan were expressed in the separation phase and migration phases whereas during the colonization phase the amount of hyaluronan was clearly diminished. This study showed that the presence of primordial germ cells in each compartment of the migratory pathway was always accompanied by a high expression of hyaluronan. These results indicate that hyaluronan is an important molecule in the migratory process, providing the primordial germ cells with a hydrated environment that facilitates their movement toward the genital ridges.

Animals↗

PubMed1988

pH-dependent phase transition of chlorpromazine micellar solutions in the physiological range.

The effects of pH and drug concentration on aggregation properties of chlorpromazine-HCl (CPZ) are examined. The critical micelle concentration (cmc) changes from 0.2 mM at pH 7.3 to 2 mM at pH 5.6 as estimated from the stearic acid spin label solubility measurements. For concentrations above the cmc CPZ micelles undergo a concentration-, temperature- and pH-dependent transition leading to phase separation. This phase transition is followed by a sudden increase of light scattering. The phase diagram pH vs. concentration is obtained by observation of the cloud point for concentrations ranging from 0.01 to 10 mM. The intramicellar environment is probed at pH ranging from 5.5 to 8.0 using a stearic acid spin label. The intramicellar compactness increases smoothly with increasing pH suggesting the weakening of polar heads repulsion due to charge decrease. The reported results indicate that pH effects are relevant and should be properly taken into account in the performance and interpretation of experiments with CPZ.

Chlorpromazine↗

PubMed1989

Thermotropic properties of mixtures of negatively charged phospholipids with cholesterol in the presence and absence of Li+ or Ca2+ ions.

Mixtures of cholesterol with dipalmitoylphosphatidylserine or phosphatidic acid were investigated by differential scanning calorimetry. As in mixtures of natural phosphatidylserine with cholesterol (Bach, D. (1984) Chem. Phys. Lipids 35, 385-392), also here phase separation of cholesterol at molar ratios of 2:1 (phospholipid:cholesterol) and below is observed. The limited solubility of cholesterol in negatively charged phospholipids is found to be independent of the nature of the acyl chain residues, and independent of whether the negative charge resides on both COO- and PO- groups (as in phosphatidylserine) or on PO- only (as in phosphatidic acid). The separate cholesterol phase is also seen by DSC in mixtures of natural phosphatidylserine or phosphatidic acid with cholesterol in the presence of Ca2+; and in phosphatidylserine/cholesterol mixtures in the presence of Li+, by DSC and X-ray diffraction.

Animals↗

PubMed1996

Synthesis and characterization of segmented polyurethanes based on amphiphilic polyether diols.

Segmented polyurethanes (SPUs) based on polyethylene glycol (PEG), polypropylene glycol (PPG) and a series of Pluronics with different ethylene oxide/propylene oxide ratios (EO/PO) and molecular weights were prepared. Different diisocyanates were used for making SPUs: 4,4-diphenylmethane diisocyanate (MDI), 4,4-dicyclohexylmethane diisocyanate (MDCI), hexamethylene diisocyanate (HMDI) and isophorone diisocyanate (IPDI). 1,4-Butane diol (BD) and ethylene diamine (ED) were used as chain extenders. The polymers obtained were characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The microphase morphology (phase separation and phase mixing) is discussed in more detail.

Biocompatible Materials↗

PubMed1991

High-performance liquid chromatographic method for the determination of nefazodone and its metabolites in human plasma using laboratory robotics.

A quantitative analytical method, using high-performance liquid chromatography and ultraviolet detection, has been established for the determination of nefazodone (NEF) and its metabolites, m-chlorophenylpiperazine (mCPP),p-hydroxynefazodone (PHN), and hydroxynefazodone (HO-NEF), in human plasma. The fully automated, robotic procedure consisted of addition of internal standard (aprindine), extraction with butyl chloride, followed by phase separation, organic phase evaporation, reconstitution of the residue, and injection onto the chromatographic system. The limits of detection for NEF, mCPP, PHN, and HO-NEF were 5, 1, 10, and 5 ng/ml, respectively, at a signal-to-noise ratio of 4. The method had a linear range of 10-1000 ng/ml for NEF and HO-NEF, 20-2000 ng/ml for PHN, and 2.5-250 ng/ml for mCPP. Correlation coefficients of 0.996 or greater were obtained during validation and study sample analysis.

Adolescent↗

PubMed2005

Granule development and performance in sucrose fed anaerobic baffled reactors.

Two 90 L anaerobic baffled reactors were used to study the granulation of sludge and the effect of the organic loading rate and NaHCO3/COD ratios on reactor performance. Furthermore, it was determined whether an anaerobic baffled reactor would promote phase separation and if additive of bentonite or granular active carbon was capable of enhancing granule formation. In order to minimize feed variations, and have a totally biodegradable substrate, a synthetic sucrose substrate was used. Granulation was achieved in both reactors within 75 days. However, the granules from the granular active carbon amended reactor appeared earlier and were larger and more compact. The reactors were maintained at a hydraulic retention time of 20 h during performance study stage. The results showed that when organic loading rate were changed from 2.15 to 6.29 kg COD m(-3)day(-1), chemical oxygen demand (COD) removal was not decreased (91-93%), but a slight increase in effluent COD was observed. It was found that the COD removals were generally good (87-92%) and had not obviously change with the decreasing NaHCO3/COD ratios. From the bacterial distribution and the concentration of volatile fatty acids in four compartments, it was concluded that a separation of phases occurred within the anaerobic baffled reactors.

Acrylic Resins↗

PubMed2002

The effect of polymer addition on granulation in an anaerobic baffled reactor (ABR). Part I: process performance.

The stability and performance of an anaerobic baffled reactor (ABR) treating an ice-cream wastewater at several organic loading rates have been investigated. Specifically, it was determined whether an ABR would promote phase separation and if a polymer additive was capable of enhancing granule formation in an ABR. In order to achieve these goals, two ABRs, having identical dimensions and configurations, were used to study the above objectives using a synthetic ice-cream wastewater. The ABR proved to be an efficient reactor configuration for the treatment of a high-strength synthetic ice-cream wastewater. An organic loading rate of around 15 kg CODm(-3) d(-1) was treated with a 99% COD removal efficiency. From the jar test and inhibition assay, it was concluded that Kymene SLX-2 was the most effective and least inhibitory polymer tested. The methane yield was higher in the polymer-amended reactor compared to the control reactor. In addition, polymer addition resulted in a considerably higher degree of biomass retention and lower solids washout from the ABR. Consequently, it demonstrated that there was a considerable potential for sludge conditioning in ABRs by facilitating better biomass retention within the reactor which in turn led to better process performance. Granulation was achieved in both ABRs within 3 months. However, the granules from the polymer-amended reactor appeared earlier and were generally larger and more compact, although this was not quantified in detail during the present study. The main advantage of using an ABR comes from its compartmentalised structure. The first compartment of an ABR may act as a buffer zone to all toxic and inhibitory material in the feed thus allowing the later compartments to be loaded with a relatively harmless, balanced and mostly acidified influent. In this respect, the latter compartments would be more likely to support active populations of the relatively sensitive methanogenic bacteria and partly explains why the best granules and the highest methane yield were obtained in Compartment 2. It is unlikely that a complete separation of phases (acidogenic and methanogenic) occurred within the ABRs since methane production was observed in all compartments, although this was low (approximately 40% of all gas composition) in Compartment 1, becoming higher (approximately 70%) in the following compartments.

Bacteria, Anaerobic↗

PubMed2003

Human SP-A and a pharmacy-grade porcine lung surfactant extract can be reconstituted into tubular myelin--a comparative structural study of alveolar surfactants using cryo-transmission electron microscopy.

Cryo-transmission electron microscopy (cryo-TEM) is a rather artefact-free method, well suited to study the alveolar surfactant system. A pharmacy grade porcine lung surfactant extract (HL-10) was mixed with human SP-A and Ringer's solution (for calcium ions), and it was shown by cryo-TEM that the tubular myelin (TM) type of structure was reconstituted. These aggregates were associated to liposomal aggregates, and resulted in macroscopic phase-separation. This phase showed a weak birefringence in the polarising microscope, which is characteristic for a liquid-crystalline type of structure. TM from rabbit lung lavage was also examined, and showed the same periodic arrangement of bilayers as alveolar surface layer from freshly cut rabbit lungs deposited directly on the cryo-TEM grids. The distance between the bilayers of TM was 40-50 nm, and an electron dense material, assumed to be SP-A, was sometimes seen to occur periodically along the bilayers, oriented perpendicularly to the tubuli. The results are consistent with the surface-phase model of the alveolar lining.

Animals↗