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PubMed1996

Effects of phase separating systems on lyophilized hemoglobin.

Polymer liquid-liquid two-phase systems offer a unique opportunity to study the mechanisms of protein stabilization during freezing and freeze-drying. Fourier transform infrared spectroscopy was used to monitor the structural integrity of recombinant hemoglobin frozen and lyophilized in the separated phases of a polyethylene glycol (PEG)-dextran system. Protein in each phase of an equilibrated biphasic PEG-dextran system experiences similar levels of structural protection against freezing stresses despite large differences in polymer concentration. This result further demonstrates previous suggestions that proteins are protected during freezing by the preferential exclusion mechanism. There are, however, distinct differences in the level of structural protection that polymers in equilibrium phases provide to proteins during lyophilization, emphasizing that the mechanisms of protein protection during freezing and drying are fundamentally different. In addition, we provide evidence that phase separation per se occurring during the course of the lyophilization cycle can be detrimental to the structural stability of a protein.

Dextrans↗

PubMed2004

Ultralow interfacial tensions in an aqueous phase-separated gelatin/dextran and gelatin/gum Arabic system: a comparison.

Many protein/polysaccharide mixtures phase separate when the concentrations ofthese biopolymers are sufficiently high. One of the properties involved in this phenomenon is the interfacial tension. Here we present measurements of the interfacial tension of two different protein/polysaccharide mixtures. The protein gelatin was mixed with either dextran or gum arabic, all used in a variety of food products. The phase diagrams were constructed using optical rotation. Although both polysaccharides have the same molecular weight, the phase diagrams differed. The interfacial tension of samples, varying in the distance from the critical point, was determined using the spinning drop method. The interfacial tension was found to be in the range of 1-15 microN/m. For both systems, the scaling behavior of the interfacial tension was investigated. The investigated gelatin/dextran system gave critical exponents of 2.5+/-0.1 and 1.4+/-0.1, in reasonable agreement with the mean-field values 3 and 1.5, respectively. The gelatin/gum arabic system did not show critical behavior. For this system, the interfacial tension shows a logarithmic dependence on the distribution of the gelatin and the gum arabic molecules in the separated phases.

Dextrans↗

PubMed2005

Preparation of bovine serum albumin loaded poly (D, L-lactic-co-glycolic acid) microspheres by a modified phase separation technique.

BSA-loaded mcirospheres were prepared by a modified phase separation method, in which petroleum ether (PE) containing a certain amount of Span 80 rather than poly (dimethylsiloxane) (PDMS) was adopted as coacervating agent. Process parameters such as Span 80 concentration, the volume and addition rate of coacervating agent, polymer concentration, agitation rate during the phase separation process and PE type were evaluated to optimize the protein encapsulation. It was found microspheres with high yield (>80.0%) and entrapment efficiency (>90%) could be obtained using PE containing 5.0% Span 80 as the coacervating agent. Microspheres with small particle size (<10 microm) could be produced successfully with appropriate process parameters. In vitro release study suggested that burst release was significantly influenced by Span 80 concentration, polymer concentration and PE type and the burst release could be reduced to <20% with optimized formulation. A biphasic release behavior in vitro test was observed for the microspheres prepared by this method. GC analysis demonstrated that residual solvent of DCM and petroleum ether was decreased dramatically in comparison with PDMS used as a conventional coacervating agent.

Alkanes↗

PubMedDate not supplied

Mechanism and kinetics of phase separation in a gelatin/maltodextrin mixture studied by small-angle light scattering.

Phase separation mechanisms and kinetics were studied using small-angle light scattering in a gelatin/maltodextrin system where phase separation could be studied in both liquid and gelled states. Nucleation and growth or spinodal decomposition occurred, depending on the quench depth. The transition between the two mechanisms occurred relatively sharply. The different mechanisms were distinguishable by the different behavior of the scattering function even though a peak was observed in both cases. Particular differences were the different evolution of the peak intensity and position, the absence of dynamic scaling of the nucleation and growth scattering function, and the final coarsening exponent of 1/3 that was measured when spinodal decomposition occurred but not for nucleation and growth. Gelation severely reduced the coarsening rate and initially placed the phase compositions far from their equilibrium values. Despite the loss of molecular mobility caused by gelation, the gelled systems did continue to evolve, albeit much more slowly than in the liquid case. Multiple coarsening rates were observed for some of the gelled samples, which were ascribed to the gradual movement of these systems toward the equilibrium compositions.

Gelatin↗

PubMed2004

Flory-Huggins model of equilibrium polymerization and phase separation in the Stockmayer fluid.

The competition between chain formation and phase separation in the Stockmayer fluid (SF) of dipolar particles is analyzed using a renormalized Flory-Huggins model of equilibrium polymerization. Calculated critical properties (T(c), phi(c), Z(c)) for the SF compare favorably with simulations over a wide range of the dimensionless dipolar (or "sticking") energy mu*. We find that the polymerization transition preempts phase separation for a large mu*, i.e., (mu*)2 >22.

Journal Article↗

PubMed2006

Texturising by phase separation.

The most common food processing operations, thermal and mechanical treatments, both affect phase state and texture of foods. The phase separation threshold for food biopolymer mixtures is usually below their concentrations characteristically found in food. Phase-separation underpins texturisation processes during food processing and digestion. The distribution of water between the phases, the adsorption of lipids between the phases, the deformation of dispersed particles in flowing water-in-water emulsions and the gelation of the phases result in the specific morphology and texture of food. A historical experience in texturisation includes the development of cooked food and texturized vegetable analogues of animal foods.

Adsorption↗

PubMed2006

Photoinduced phase separation.

A novel approach of photoinduced phase separation has been demonstrated with a photolabile anionic surfactant, mixed with an inert nonionic surfactant in the presence of salting-out electrolyte. Breakdown of the photolyzable surfactant results in hydrophobic photoproducts, which are emulsified by the remaining inert surfactant; added electrolyte resolves the emulsion into macroscopic oily and aqueous phases. The initial micellar systems can disperse an insoluble additive marker dye (shown), which may be spatially segregated from the aqueous environment by the action of UV light.

Journal Article↗

PubMed2006

Wetting-induced depletion interaction between particles in a phase-separating liquid mixture.

Inclusion of solid particles drastically affects the pattern evolution of phase separation of a binary fluid mixture, via preferential wetting of one of the phases to the particles. Here we study this problem by numerical simulation, which incorporates interparticle hydrodynamic interactions properly. When particles favor one of the components of a mixture, wetting layers are quickly formed on the particle surfaces and all particles are eventually included into the more wettable phase. For immobile particles, domains of the more wettable phase are pinned to the particles and the domain growth is thus suppressed. For this case, the domain size at a certain phase-separation time decreases monotonically with increasing the particle concentration. For mobile particles, on the other hand, the reentrant morphological transformation is observed as a function of the particle concentration: With an increase in the particle concentration, the domain morphology of the more wettable phase sequentially changes from network, droplet to network. We found that the final morphological transition is induced by wetting-induced depletion interaction: strong attractive interactions act among particles when the total volume of the more wettable phase is not enough to cover all the particles by wetting layers.

Journal Article↗

PubMed1999

Diffusiophoresis of two-dimensional liquid droplets in a phase-separating system.

The motion of phase-separating liquid drops was simulated in two dimensions following the model H, where convection and diffusion are coupled via a body force, expressing the tendency of demixing systems to minimize their free energy. This driving force depends on the capillary number, i.e., the ratio of viscous to thermal forces, which in a typical case is of order 10(-4), inducing a convective material flux much larger than its diffusive counterpart. Three problems were considered. In the first, we studied the motion of a single drop immersed in a continuum field with constant concentration gradient, finding that the drop speed is proportional to the concentration gradient and inversely proportional to the capillary number. In the second problem, we found that the motion of a single drop immersed in a homogeneous concentration field depends on the difference (Delta(phi))(0) between the initial concentration of the continuum phase and its equilibrium value. In fact, when (Delta(phi))(0)<0, the drop shrinks without moving, while when (Delta(phi))(0)>0, the drop consumes material from the surrounding field and moves randomly, propelled by the induced capillary driving force. During its movement, the drop grows linearly in time, with a growth rate proportional to the ratio between molecular diffusivity and interface thickness. In addition, during its random motion, the drop mean square displacement grows linearly with time, with an effective diffusion coefficient which is of the same magnitude as the molecular diffusivity. The predicted drop growth rate and mean velocity are in good agreement with experimental observations. Finally, the motion of two drops is studied, showing that the capillary forces induce a mutual attraction between the two drops. When (Delta(phi))(0)<0, the attractive force is unchallenged, thus leading always to coalescence, while when (Delta(phi))(0)>0 a screening effect arises which may keep the two drops apart from each other.

Journal Article↗

PubMed2006

Phase separation of a model binary polymer solution in an external field.

The phase separation of a simple binary mixture of incompatible linear polymers in solution is investigated using an extension of the sedimentation equilibrium method, whereby the osmotic pressure of the mixture is extracted from the density profiles of the inhomogeneous mixture in a gravitational field. In Monte Carlo simulations the field can be tuned to induce significant inhomogeneity, while keeping the density profiles sufficiently smooth for the macroscopic condition of hydrostatic equilibrium to remain applicable. The method is applied here for a simplified model of ideal but mutually avoiding polymers, which readily phase separate at relatively low densities. The Monte Carlo data are interpreted with the help of an approximate bulk phase diagram calculated from a simple, second-order virial coefficient theory. By derivation of effective potentials between polymer centers of mass, the binary mixture of polymers is coarse-grained to a "soft colloid" picture reminiscent of the Widom-Rowlinson model for incompatible atomic mixtures. This approach significantly speeds up the simulations and accurately reproduces the behavior of the full monomer resolved model.

Journal Article↗

PubMed2006

Membrane-adhesion-induced phase separation of two species of junctions.

A theory of membrane-adhesion-induced phase separation of two species of ligand-receptor complexes (i.e., junctions) is presented. Different species of junctions are assumed to have different natural heights and flexibilities. It is shown that the equilibrium properties of the system are equivalent to a membrane under an effective external potential, and for given junction flexibility difference phase separation occurs at sufficiently large junction height difference. The phase coexistence curve shows two distinct regions. (i) When junction height difference is large, the system is far from the mean-field critical point. Because of the higher entropy associated with softer junctions, phase coexistence occurs when the harder junctions have higher effective binding energy (free energy released due to the formation of a junction). (ii) When junction height difference is small such that the system is near the mean-field critical point, the contribution of the binding energy of the softer junctions to the free energy of the state with intermembrane distance close to the natural height of the harder junctions is not negligible. Therefore phase coexistence occurs when the harder junctions have smaller effective binding energy. Monte Carlo simulation that studies the effect of non-Gaussian fluctuations on the critical point indicates that the situation described in (ii) can be observed in typical biological systems.

Journal Article↗

PubMed2004

Liquid phase separator with chromatographic column.

Presented liquid phase separator with integrated chromatographic column enables the separation and treatment of a solvent extract layer after the extraction of organic compounds from water in one simple run in a single piece of glassware. The separator has been successfully applied for the determination of hydrocarbon oil index in waters.

Chromatography, Liquid↗

PubMed2004

A Langevin dynamics study of mobile filler particles in phase-separating binary systems.

The dynamics of phase separation in a simple binary mixture containing mobile filler particles that are preferentially wet by one of the two components is investigated systematically via Langevin simulations in two dimensions. We found that while the filler particles reduce the growth rate of spinodal decomposition, the domain growth remains essentially identical to that of the pure binary mixture. The growth rate diminishes as either the filler particles concentration is increased or their diffusivity is decreased.

Journal Article↗

PubMed2003

Traveling waves in phase-separating reactive mixtures.

A model of phase separation of chemically reactive ternary mixtures is constructed. In this model, spatially periodic structures that coherently propagate at a constant speed emerge through a Hopf bifurcation at a finite wave number. It is shown by computer simulations that both lamellar and hexagonal structures undergo a coherent propagating motion in two dimensions, and there are two types of traveling hexagons depending on the relative direction between the traveling velocity and the lattice vectors of the hexagonal structure. Amplitude equations for the traveling waves are derived, and the stability of the traveling and standing waves is discussed.

Journal Article↗

PubMed2001

Phase separation in a chaotic flow.

The phase separation between two immiscible liquids advected by a bidimensional velocity field is investigated numerically by solving the corresponding Cahn-Hilliard equation. We study how the spinodal decomposition process depends on the presence-or absence-of Lagrangian chaos. A fully chaotic flow, in particular, limits the growth of domains, and for unequal volume fractions of the liquids, a characteristic exponential distribution of droplet sizes is obtained. The limiting domain size results from a balance between chaotic mixing and spinodal decomposition, measured in terms of Lyapunov exponent and diffusivity constant, respectively.

Journal Article↗

PubMed1983

Thermotropic lipid phase separations in human platelet and rat liver plasma membranes.

Electron spin resonance (ESR) studies were conducted on human platelet plasma membranes using 5-nitroxide stearate, I(12,3). The polarity-corrected order parameter S and polarity-uncorrected order parameters S(T parallel) and S(T perpendicular) were independent of probe concentration at low I(12.3)/membrane protein ratios. At higher ratios, S and S(T perpendicular) decreased with increasing probe concentration while S(T parallel) remained unchanged. This is the result of enhanced radical interactions due to probe clustering. A lipid phase separation occurs in platelet membranes that segregates I(12,3) for temperatures less than 37 degrees C. As Arrhenius plots of platelet acid phosphatase activity exhibit a break at 35 to 36 degrees C, this enzyme activity may be influenced by the above phase separation. Similar experiments were performed on native [cholesterol/phospholipid ratio (C/P) = 0.71] and cholesterol-enriched [C/P = 0.85] rat liver plasma membranes. At 36 degrees C, cholesterol loading reduces I(12,3) flexibility and decreases the probe ratio at which radical interactions are apparent. The latter effects are attributed to the formation of cholesterol-rich lipid domains, and to the inability of I(12,3) to partition into these domains because of steric hinderance. Cholesterol enrichment increases both the high temperature onset of the phase separation occurring in liver membranes from 28 degrees to 37 degrees C and the percentage of probe-excluding, cholesterol-rich lipid domains at elevated temperatures. A model is discussed attributing the lipid phase separation in native liver plasma membranes to cholesterol-rich and -poor domains. As I(12,3) behaves similarly in cholesterol-enriched liver and human platelet plasma membranes, cholesterol-rich and -poor domains probably exist in both systems at physiologic temperatures.

Acid Phosphatase↗

PubMed2005

Particle-induced phase separation in mixed polymer solutions.

The influence of added colloidal particles on the phase separation of mixed aqueous polymer solutions is investigated. Two types of particles (polystyrene latex or silica) and different combinations of segregating polymers (dextran of varying molar mass combined with poly(ethylene oxide) (PEO) of varying molar mass, or Ucon, a copolymer of ethylene oxide and propylene oxide) were used. All systems displayed particle-induced instability effects, but the extent of the effect varied strongly between the various combinations and with the amount of added salt. Very large instability effects were seen in certain mixtures. Two mechanisms, both relying on the adsorption of at least one of the polymers to the particle surface, seem to operate. Close to the cloud-point curve of the particle-free polymer1/polymer2/water mixture, adsorption of PEO or Ucon to the particles gives rise to a capillary-induced phase separation. Close to the dextran/water axis of the phase diagram, the adsorbing polymer gives rise to a surface modification of the particles, which then interacts repulsively with the surrounding dextran solution.

Journal Article↗

PubMed2004

[Determination of zinc in mineral by FAAS after phase separation and extraction].

Non-ion surface active agent can be separated from its solution of water by heating to its cloud point. A new method for the determination of zinc in mineral samples by flame atomic absorption spectrophotometer after phase separation and extraction making use of its cloud point was studied in this paper. The conditions of phase separation and extraction such as using Triton X-100 as phase separation agent, and octanol to drop the cloud point, and the influence of acidity and the number of times for oscillating were discussed. The detection limit was 0.005 microg x mL(-1). This method has been applied to the determination of zinc in ores with satisfactory results.

Phase Transition↗