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 307 records · Page 17Linked to original sources

PubMed1987

Aluminum-induced lipid phase separation and membrane fusion does not require the presence of negatively charged phospholipids.

The interaction of Aluminum with phosphatidyl serine lipid vesicles containing variable amounts of phosphatidyl ethanolamine, phosphatidyl choline and cholesterol has been studied by lipid phase separation monitored by fluorescence quenching. The interaction of Al3+ with neutral phospholipid membranes has also been investigated. Maximal lipid phase separation can be demonstrated in mixed phosphatidyl ethanolamine-cholesterol vesicles when using concentrations of aluminum between 87.5 and 125 microM. Millimolar concentrations of Ca2+, Mn2+, Cd2+ and Zn2+ were without any effect. Aluminum also induced fusion of phospholipid membranes monitored by resonance energy transfer between N-(7-nitro-2,1,3, benzoxadiazol-4 yl) phosphatidyl ethanolamine and N-(lissamine Rhodamine B-sulfonyl) phosphatidyl ethanolamine, either when containing low amounts of phosphatidyl serine (12.5%) or without any negatively charged phospholipid. Aluminum-induced fusion of liposomes was also monitored by the fluorescence of the terbium-dipicolinic acid complex (Tb-DPA3-) formed during fusion of vesicles containing either Tb-(citrate)6- complex or sodium salt of dipicolinic acid.

Aluminum↗

PubMed2006

Particle tracking using confocal microscopy to probe the microrheology in a phase-separating emulsion containing nonadsorbing polysaccharide.

Brownian diffusion of fluorescent microspheres (0.21, 0.5, and 0.89 microm diameter) in conjunction with confocal microscopy has been used to monitor the microrheology of phase-separated regions in a protein-stabilized oil-in-water emulsion containing various low concentrations of a nonadsorbing polysaccharide, xanthan gum. The sensitivity and reliability of the technique has been demonstrated in test experiments on (i) aqueous glycerol solutions and (ii) concentrated surfactant-stabilized emulsions (30-60 vol % oil, 1-2 wt % Tween 20). From particle tracking measurements on the caseinate-stabilized emulsions (30 vol % oil, 1.4 wt % sodium caseinate, pH 7) containing xanthan (0.03-0.07 wt %), the apparent viscosity in the oil-droplet-rich regions has been estimated to be up to 10(3) times higher than that in the phase-separated xanthan-rich regions. This means that our previously determined shape relaxation times for xanthan-containing blobs in the same systems can be attributed to the dominant viscoelasticity of the surrounding regions of concentrated oil droplets and not to the rheology of the xanthan-rich blobs themselves. These data provide clear and unequivocal evidence for the dominant role of the interconnected depletion-flocculated network of oil droplets in the physicochemical mechanism by which hydrocolloid thickeners control the creaming instability of concentrated oil-in-water emulsions.

Adsorption↗

PubMed2005

Oscillatory instabilities in phase separation of binary mixtures: fixing the thermodynamic driving.

Binary liquid mixtures can show pronounced oscillations in the differential scanning calorimeter signal for the specific heat and in the turbidity when phase separation is induced by continuously ramping the temperature. For a fixed ramp rate, i.e., a linear temporal drift of temperature, only a small number of oscillations have been observed. In the present manuscript we describe an experimental setup where simultaneous video-microscopy and shadow-graph measurements can be performed on mixtures subjected to an arbitrary temporal temperature evolution. In particular, it can be adjusted to fix the thermodynamic driving force, which characterizes the rate of change of the composition of the coexisting phases. With this novel technique both the number of oscillations and the temperature interval where oscillations are observed increase significantly. This technique can easily be applied to a great variety of binary mixtures, permitting detailed investigations of their phase-separation kinetics under slowly ramping temperature.

Journal Article↗

PubMed1984

Thermotropic lipid phase separations in human erythrocyte ghosts and cholesterol-enriched rat liver plasma membranes.

Electron spin resonance (ESR) studies of human erythrocyte ghosts labeled with 5-nitroxide stearate, I(12,3), indicate that a temperature-dependent lipid phase separation occurs with a high onset at 38 degrees C. Cooling below 38 degrees C induces I(12,3) clustering. Similar phase separations were previously identified in human platelet and cholesterol-loaded [cholesterol/phospholipid molar ratio (C/P) = 0.85] rat liver plasma membranes [L.M. Gordon et al., 1983; J. Membrane Biol. 76; 139-149]; these were attributed to redistribution of endogenous lipid components such that I(12,3) is excluded from cholesterol-rich domains and tends to reside in cholesterol-poor domains. Further enrichment of rat liver plasma membranes to C/P ratios of 0.94-0.98 creates an "artificial" system equivalent to human erythrocyte ghosts (C/P = 0.90), using such criteria as probe flexibility, temperature dependent I(12,3) clustering; and polarity of the probe environment. Consequently, cholesterol-rich and -poor domains probably exist in both erythrocyte ghosts and high cholesterol liver membranes at physiologic temperatures. The temperature dependence of cold-induced hypertonic lysis of intact human erythrocytes was examined by incubating cells in 0.9 M sucrose for 10 min at 1 degree C intervals between 9 and 46 degrees C (Stage 1), and then subjecting them to 0 degrees C for 10 min (Stage 2). Plots of released hemoglobin are approx. sigmoidal, with no lysis below 18 degrees C and maximal lysis above 40 degrees C. The protective effect of low temperatures during Stage 1 may be due to the formation of cholesterol-rich domains that alter the bilayer distribution and/or conformation of critical membrane-associated proteins.

Animals↗

PubMed1992

Evolution of a phase separated gravity independent bioreactor.

The evolution of a phase-separated gravity-independent bioreactor is described. The initial prototype, a zero head-space manifold silicone membrane based reactor, maintained large diffusional resistances. Obtaining oxygen transfer rates needed to support carbon-recycling aerobic microbes is impossible if large resistances are maintained. Next generation designs (Mark I and II) mimic heat exchanger design to promote turbulence at the tubing-liquid interface, thereby reducing liquid and gas side diffusional resistances. While oxygen transfer rates increased by a factor of ten, liquid channeling prevented further increases. To overcome these problems, a Mark III reactor was developed which maintains inverted phases, i.e., media flows inside the silicone tubing, oxygen gas is applied external to the tubing. This enhances design through changes in gas side driving force concentration and liquid side turbulence levels. Combining an applied external pressure of four atmospheres with increased Reynolds numbers resulted in oxygen transfer intensities of 232 mmol O2/l/h (1000 times greater than first prototype and comparable to a conventional fermenter). A 1.0 liter Mark III reactor can potentially deliver oxygen supplies necessary to support cell cultures needed to recycle a 10 astronaut carbon load continuously.

Atmospheric Pressure↗

PubMed2006

Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water.

The authors present a model describing the coexistence of hydrophobic association and phase separation with lower critical solution temperature (LCST) in aqueous solutions of polymers carrying short hydrophobic chains at both chain ends (telechelic associating polymers). The LCST of these solutions is found to decrease along the sol/gel transition curve as a result of both end-chain association (association-induced phase separation) and direct hydrophobic interaction of the end chains with water. The authors relate the magnitude of the LCST decrease to a hydration cooperativity parameter sigma. The LCST decreases substantially (approximately 100 K) in the case of random hydration (sigma=1), whereas only a small shift (approximately 5-10 K) occurs in the case of cooperative hydration (sigma=0.3). The molecular weight dependence of the LCST drop is studied in detail in each case. The results are compared with experimental observations of the cloud points of telechelic poly(ethylene oxide) solutions, in which random hydration predominates, and of telechelic poly(N-isopropylacrylamide) solutions, in which cooperative hydration prevails.

Journal Article↗

PubMed2000

Crossover from the hydrodynamic regime to the thermal fluctuation regime in a two-dimensional phase-separating binary fluid containing surfactants

Extensive simulations were carried out to investigate the crossover between the hydrodynamic regime at intermediate stage and the thermal fluctuation regime at late stage in a phase-separating binary fluid/surfactant system in two dimensions. The existence of the crossover and its dependence on the surfactant concentration were analyzed using Kawasaki and Ohta's interface kinetic equation [Physica A 118, 175 (1983)]. The analysis showed that there should exist a critical surfactant concentration, above which thermal fluctuations dominate phase separation at all times. Simulations suggested that the crossover exists and the hydrodynamic regime shrinks when surfactant concentration increases. Simulations also demonstrated that the trapped surfactants seen in a previous study [Phys. Rev. E 59, 2109 (1999)] can remain trapped for a time much longer than the time needed to form well segregated domains, in spite of the presence of significant thermal fluctuations.

Journal Article↗

PubMed2004

Confinement effect on the adsorption from a binary liquid system near liquid/liquid phase separation.

The preferential adsorption of one component of a binary system at the inner surfaces of mesoporous silica glasses was studied in a wide composition range at temperatures close to liquid/liquid phase separation. Confinement effects on the adsorption were investigated by using three controlled-pore glass (CPG-10) materials of different mean pore size (10 to 50 nm). For the experimental system (2-butoxyethanol+water), which exhibits an upper miscibility gap, strong preferential adsorption of water occurs, as the coexistence curve is approached at bulk compositions, at which water is the minority component. In this strong adsorption regime the area-related surface excess amount of adsorbed water decreases with decreasing pore width, while the shift in the volume-related mean composition of the pore liquid shows an opposite trend, i.e., greatest deviation from bulk composition occurring in the most narrow pores. A simple mean-field lattice model of a liquid mixture confined by parallel walls is adopted to rationalize these experimental findings. This model reproduces the main findings of the confinement effect on the adsorption near liquid/liquid phase separation.

Journal Article↗

PubMed1976

The evolutionary significance of phase-separated microsystems.

The source, preparation, and properties of phase-separated systems such as lipid layers, coacervate droplets, sulphobes, and proteinoid microspheres are reviewed. These microsystems are of interest as partial models for the cell and as partial or total models for the protocell. Conceptual benefits from study of such models are: clues to experiments on origins, insights into principles of action and, in some instances, presumable models of the origin of the protocell. The benefits to evolution of organized chemical units are many, and can in part be analyzed. Ease of formation suggests that such units would have arisen early in primondiae organic evolution. Integration of these various concepts and the results of consequent experiments have contributed to the developing theory of the origins of primordial and of contemporary life.

Cells↗

PubMed2000

Phase-separated composite films: experiment and theory

A different phase-separation process is capable of producing a composite system consisting of a very thin layer of liquid crystal in contact with a similarly thin layer of polymer. The morphology of the polymer depends on the composition of the prepolymer-liquid crystal mixture and the rate of polymerization. A simple one-dimensional theory is able to describe the essential features of this process.

Journal Article↗

PubMed2002

Dynamics of phase separation in multicomponent mixtures.

We study the dynamics of phase separation in multicomponent mixtures through Monte Carlo simulations of the q-state Potts model with conserved kinetics. We use the Monte Carlo renormalization-group method to investigate the asymptotic regime. The domain growth law is found to be consistent with the Lifshitz-Slyozov law, L(t) equivalent to t(1/3) (where t is time), regardless of the value of q. We also present results for the scaled correlation functions and domain-size distribution functions for a range of q values.

Journal Article↗

PubMed1999

Purification of recombinant and human apolipoprotein A-1 using surfactant micelles in aqueous two-phase systems: recycling of thermoseparating polymer and surfactant with temperature-induced phase separation.

An effective system has been developed for purification of apolipoprotein A-1 from Escherichia coli fermentation solution and human plasma using aqueous two-phase extraction and thermal-phase separation. The system included non-ionic surfactants (Triton or Tween) and as top phase-forming polymer a random copolymer of ethylene oxide (50%) and propylene oxide (50%), Breox PAG 50A 1000, was used. The bottom phase-forming polymer was either hydroxypropyl starch, Reppal PES 100 and PES 200, or hydroxyethyl starch, Solfarex A 85. The top-phase-forming polymer and the surfactants are thermoseparating in water solution, i.e., when heated a water phase and a polymer/surfactant phase are formed. Recombinant apolipoprotein A-1, the Milano variant, was extracted from E. coli fermentation solution in a primary Breox-starch phase system followed by thermal separation of the Breox phase where the target protein was recovered in the water phase. Both in the Breox-starch system and in the water-Breox system Triton X-100 was partitioned to the Breox phase. The addition of non-ionic surfactants to the Breox-starch system had strong effect on the purification and yield of the amphiphilic apolipoprotein A-1. In a system containing 17% Breox PAG 50A 1000, 12% Reppal PES 100 and addition of 1% Triton X-100 the purification factor was 7.2, and the yield 85% after thermal separation of the Breox phase. Recycling of copolymer and surfactant was possible after thermal separation of copolymer phase. Approximately 85% of the copolymer and surfactant could be recycled in each extraction cycle. DNA could be strongly partitioned to the starch phase in the primary-phase system. This resulted in a 1000-fold reduction of E. coli DNA in the apolipoprotein A-1 solution obtained after thermoseparation. In extraction from human plasma containing low concentrations of apolipoprotein A-1, it was possible to reach a purification factor of 420 with 98% yield. By reducing the volume ratio to 0.1 Apo A-1 could be concentrated in a small volume of top phase (concentration factor 10) with a yield of 85% and a purification factor of 110.

Apolipoprotein A-I↗

PubMed2000

Gelation by phase separation in a whey protein system: in-situ kinetics of aggregation.

The aggregation and gelation properties of beta-lactoglobulin (BLG), a globular protein from milk, was studied in aqueous ethanol solutions at room temperature. The phase state diagrams as a function of pH and ethanol concentration showed that a gel structure appeared after a period ranging from 1 min to 1 week, depending on the physico-chemical conditions. The in-situ kinetics of aggregation were followed by several methods in order to obtain a better understanding of the building of aggregates by the addition of ethanol. It was shown that the aggregation kinetics highly depended upon the pH, the process being fastest at pH 7. Viscoelasticity and infrared measurements indicated that alcohol-induced gelation would proceed via a two-step mechanism: small aggregates loosely connected between them were first built up; a real network took place in a second step. The coarse and irregular structures formed in aqueous ethanol gels revealed by confocal laser scanning microscopy could be analysed in terms of a phase separation. This observation was supported by a syneresis phenomenon visible in the final gel state. BLG in water-ethanol solution would undergo either an inhibition of the demixing by gelation or a binary phase separation accompanied by an irreversible gelation transition.

Ethanol↗

PubMed1987

Inhibition of phase separation by reagents that prevent X-irradiation cataract in vivo.

Galactose, and the phosphorothioates, WR-77913 and WR-2721, which inhibit cataract produced by X-irradiation, were evaluated for their effects on the phase separation temperature, Tc, of calf lens homogenate. The reagents were added to nuclear homogenate and the change in Tc per mol, dTc/dC, was measured. Galactose decreased Tc, -65 degrees C mol-1, WR-77913 decreased Tc, -28 degrees C mol-1 and WR-2721 decreased Tc, -76 degrees C mol-1. These are the first phase separation inhibitors that can be used in vivo to study the inhibition of lens opacification.

Amifostine↗

PubMed1990

Calcium-induced lipid phase separations and interactions of phosphatidylcholine/anionic phospholipid vesicles. Fluorescence studies using carbazole-labeled and brominated phospholipids.

A novel method that uses a carbazole-labeled fluorescent phosphatidylcholine, which partitions preferentially into liquid-crystalline lipid domains, to monitor the kinetics and the extents of thermotropic and ionotropic lateral phase separations in vesicles combining brominated and nonbrominated phosphatidylcholines (PCs), phosphatidic acids (PAs), and phosphatidylserines (PSs) is described. The calcium-induced segregation of several nonbrominated PA species in liquid-crystalline brominated PC bilayers behaves as a well-defined lateral phase separation; the residual solubility of the PA component in the PC-rich phase in the presence of calcium can vary severalfold depending on the PA acyl chain composition. PC/PS mixtures show a pronounced tendency to form metastable solutions in the presence of calcium, particularly when they contain less than equimolar proportions of PS. This metastability is not readily relaxed by repeated freeze-thawing of vesicles in the presence of calcium, by avidin-mediated contacts between PC/PS vesicles containing biotinylated lipids, or by calcium-induced lateral segregation of PA in the same vesicles. Different PS species exhibit different apparent residual solubilities in liquid-crystalline PC bilayers, ranging from less than 10 mol % for dimyristoyl-PS to ca. 45 mol% for dioleoyl-PS, after prolonged incubations of PC/PS multilamellar vesicles with excess calcium. Results are presented, obtained by using the above lipid-segregation assay and parallel assays of intervesicle lipid mixing, that raise questions concerning the relevance of the equilibrium behavior of calcium-treated PS/PC mixtures to the relatively rapid interactions (fusion and lipid mixing) of PC/PS vesicles that follow initial exposure to calcium.

Bromine↗

PubMed2000

Ultra-small-angle neutron scattering studies on phase separation of poly(vinyl alcohol) gels

Time-resolved light scattering measurements during the gelation process of a poly(vinyl alcohol) (PVA) solution in a mixture of dimethyl sulfoxide and water (H2O) have shown that a spinodal decomposition (SD) type phase separation takes place in the early stage of gelation. In this case the kinetics of SD is valid only before macroscopic gelation occurs because the growth rate is slowed down by gelation. Such SD type phase separation makes the solution opaque as it proceeds, and hence the structural change can no longer be followed by light scattering. To investigate the structure of the opaque PVA gel as well, we have employed an ultra-small-angle neutron scattering technique using a Bonse-Hart camera. These observations reveal that even after the macroscopic gelation the structure due to the microphase separation on a spatial scale of several &mgr;m continues to grow against the elasticity. This may be because at first the gel structure is too soft to suppress the growth of the microphase separation, but within 24 h after the quenching the growth terminates. On the basis of the results, we will discuss a possible mechanism of the microphase separation after gelation.

Journal Article↗

PubMed2006

Flow-injection solvent extraction without phase separation. Fluorimetric determination of thiamine by the thiochrome method.

Two modes of liquid-liquid extraction in flow-injection systems were compared and applied to the fluorimetric determination of thiamine (Vitamin B(1)). The first included phase segmentation, but fluorescence was measured without phase separation. In this mode, thiamine was detected at concentrations higher than 8 microg/l with a linear application range of 30-2,000 microg/l, an R.S.D. of 1.9% (150 microg/l, n=10) and a sampling frequency of 60/h. In the second mode, a single segment of organic solution was injected into the aqueous stream and fluorescence was also measured without phase separation. Using this mode, concentrations of thiamine higher than 1 microg/l were detected, with a linear application range between 5 and 280 microg/l, an R.S.D. of 2.4% (150 microg/l, n=10) and a sampling frequency of 60/h. The two forms were applied to the analysis of thiamine in pharmaceuticals.

Flow Injection Analysis↗

PubMed2000

In situ atomic force microscopic observation of albumin adsorption onto phase-separated organosilane monolayer surface.

A mixed (n-octadecyltrichlorosilane (OTS)/[2-(perfluorooctyl)ethyl]trichlorosilane (FOETS)) monolayer was prepared on the water subphase and was subsequently immobilized onto the silicon wafer surface by chemical bonds. Atomic force microscopic (AFM) observation of the mixed (OTS/FOETS) monolayer revealed the formation of a phase-separated structure. In situ AFM observation of the adsorption behavior of bovine serum albumin (BSA) onto the mixed (OTS/FOETS) monolayers, successfully showed the adsorption behavior of BSA onto the phase-separated surface. It also revealed that in the case of pH 7.5, BSA was preferentially adsorbed onto the lower surface free energy FOETS phase of the mixed (OTS/FOETS) monolayer. On the other hand, BSA was adsorbed homogeneously onto the OTS and FOETS phases at the isoelectric point of BSA (pI 4.7). These results indicate that the preferential adsorption of BSA onto the FOETS phase in the mixed (OTS/FOETS) monolayer system may be due to: (1) the minimization of interfacial free energy between a monolayer surface and an aqueous solution; and (2) the electrostatic repulsion among BSA molecules bearing negative charges.

Adsorption↗