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PubMed2000

Characterizations of critical processes in liquid-liquid phase separation of the elastomeric protein-water system: microscopic observations and light scattering measurements.

Biological self-assembly process of tropoelastin in an extracellular space, viewed as a key step of the elastogenesis, can be mimicked by the temperature-dependent coacervation of the elastin-related polypeptide-water system. Early and late stages of the phase separation behavior of the bovine neck ligamental alpha-elastin-water system were examined respectively by the laser light scattering photometry and phase contrast microscopy. Changes in the hydrodynamic size of molecular assemblies and visible microcoacervate droplet size were traced as a function of the concentration of alpha-elastin and temperature. Near the critical point, alpha-elastin concentration of 0.11 mg/mL and temperature of 21.5 degrees C, the phase separation was initiated after fast increase of the hydrodynamic size of primary aggregates as scattering particles and followed by the appearance of larger microcoacervate droplets with a broad size distribution. Whereas in the off-critical region, slow decrease of the hydrodynamic size of primary particles induced phase separation with smaller droplets of a narrow size distribution. Observation of the phase separation processes in the alpha-elastin-water system with metal chlorides and hydrophobic synthetic model polypeptide-water system indicated that the fast and slow molecular assembly processes were based on the fundamental hydrophobic interactions and involvements of electrostatic interactions between charged amino acid residues, respectively.

Animals↗
PubMed2001

Shear viscosity of phase-separating polymer blends with viscous asymmetry.

Rheo-optical measurements of phase separating polymer mixtures under simple shear flow have been used to investigate the influence of domain morphology on the viscosity of emulsionlike polymer blends, in which the morphology under weak shear is droplets of one coexisting phase dispersed in a matrix of the second. The structure and viscosity of low-molecular-weight polybutadiene and polyisoprene mixtures, phase separated by quenching to a temperature inside the coexistence region of the phase diagram, were measured as a function of shear rate and composition. In the weak shear regime, the data are in qualitative agreement with an effective medium model for non-dilute suspensions of slightly deformed interacting droplets. In the strong shear regime, where a stringlike pattern appears en route to a shear-homogenized state, the data are in qualitative agreement with a simple model that accounts for viscous asymmetry in the components.

Journal Article↗
PubMed2003

Adhesion-induced phase separation of multiple species of membrane junctions.

A theory is presented for the intermembrane junction separation induced by the adhesion between two biomimetic membranes that contain two different types of anchored intermembrane junctions (receptor-ligand complexes). The analysis shows that several mechanisms contribute to the phase separation of the membrane junctions. These mechanisms include the following. (i) The elasticity of the membranes mediates a short-ranged nonlocal interaction between the junctions due to the height difference between type-1 and type-2 junctions. This is the main factor that drives the phase separation. (ii) When type-1 and type-2 junctions have different flexibilities against stretch and compression, the "softer" junctions are the "favored" species, and aggregation of the softer junctions can occur. (iii) The thermally activated shape fluctuations of the membranes also contribute to the phase separation by inducing another nonlocal interaction between the junctions and renormalizing the binding energy of the junctions. The combined effect of these mechanisms is that when phase separation occurs, the system separates into two domains with different relative and total junction densities.

Biophysical Phenomena↗
PubMed2003

Correlating structure with fluorescence emission in phase-separated conjugated-polymer blends.

Blends of conjugated polymers are frequently used as the active semiconducting layer in light-emitting diodes and photovoltaic devices. Here we report the use of scanning near-field optical microscopy, scanning force microscopy and nuclear-reaction analysis to study the structure of a thin film of a phase-separated blend of two conjugated polymers prepared by spin-casting. We show that in addition to the well-known micrometre-scale phase-separated morphology of the blend, one of the polymers preferentially wets the surface and forms a 10-nm-thick, partially crystallized wetting layer. Using near-field microscopy we identify unexpected changes in the fluorescence emission from the blend that occurs in a 300-nm-wide band located at the interface between the different phase-separated domains. Our measurements provide an insight into the complex structure of phase-separated conjugated-polymer thin films. Characterizing and controlling the properties of the interfaces in such films will be critical in the further development of efficient optoelectronic devices.

Crystallization↗
PubMed2005

Phase separation in Jahn-Teller systems with localized and itinerant electrons.

The phase diagram for doped manganites and related compounds is analyzed in terms of the Kondo-lattice model taking into account an interplay between electrons localized due to lattice distortions and those in the band states. It is shown that the number of itinerant charge carriers can be significantly lower than that implied by the doping level. The competition between the homogeneous (ferromagnetic or antiferromagnetic) and phase-separated states is discussed and a strong tendency to the phase separation was revealed for a wide doping range.

Journal Article↗
PubMed1986

Micromolar concentrations of Zn2+ potentiates Ca2+-induced phase separation of phosphatidyl serine containing liposomes.

Fluorescence quenching of 1-acyl-2-[6[(7 nitro-2,1,3-benzoxadiazol-4yl) amino]caproyl] phosphatidyl choline in small unilamellar vesicles consisting of phosphatidyl serine has been used to monitor the lipid phase separation induced by Zn2+ and Ca2+. Phase separation of vesicle membranes was observed with Zn2+ at concentrations as low as 125 microM. Low concentrations of Zn2+ required long incubation times to reach maximal quenching (120 minutes at 375 microM). When low concentrations of Ca2+ were added to the preparation during the developing phase of Zn2+-induced quenching, an explosive increase in fluorescence quenching was instantenously observed. Phase separation induced by sub-millimolar concentrations of Ca2+ could be increased at least 4 times when vesicles were pre-incubated with 250 microM of Zn2+.

4-Chloro-7-nitrobenzofurazan↗
PubMed1998

Protein inactivation in amorphous sucrose and trehalose matrices: effects of phase separation and crystallization.

Trehalose is the most effective carbohydrate in preserving the structure and function of biological systems during dehydration and subsequent storage. We have studied the kinetics of protein inactivation in amorphous glucose/sucrose (1:10, w/w) and glucose/trehalose (1:10, w/w) systems, and examined the relationship between protein preservation, phase separation and crystallization during dry storage. The glucose/trehalose system preserved glucose-6-phosphate dehydrogenase better than did the glucose/sucrose system with the same glass transition temperature (Tg). The Williams-Landel-Ferry kinetic analysis indicated that the superiority of the glucose/trehalose system over the glucose/sucrose system was possibly associated with a low free volume and a low free volume expansion at temperatures above the Tg. Phase separation and crystallization during storage were studied using differential scanning calorimetry, and three separate domains were identified in stored samples (i.e., sugar crystals, glucose-rich and disaccharide-rich amorphous domains). Phase separation and crystallization were significantly retarded in the glucose/trehalose system. Our data suggest that the superior stability of the trehalose system is associated with several properties of the trehalose glass, including low free volume, restricted molecular mobility and the ability to resist phase separation and crystallization during storage.

Chemical Phenomena↗
PubMed2000

Incompatibility and Phase Separation in a Bovine Serum Albumin/beta-Casein/Water Ternary Film at the Air-Water Interface.

Thermodynamic incompatibility and two-dimensional phase separation in a bovine serum albumin (BSA)/beta-casein/water ternary film at the air-water interface has been studied using an epifluorescence microscopy technique. The incompatibility between BSA and beta-casein at the air-water interface was deduced from deviation of the experimental equilibrium composition of the proteins in the mixed saturated monolayer film from that predicted by the Langmuir-type competitive adsorption model at various bulk concentration ratios. Fluorescence microscopy of the mixed monolayer film showed distinct phase-separated BSA-rich and beta-casein-rich regions coexisting with inhomogeneous mixed regions. BSA always tended to be the dispersed phase and beta-casein the continuous phase. It is suggested that because the free energy at the "interfaces" between the phase-separated regions is generally higher than at other regions of the film, they may act as zones of instability in protein-stabilized foams and possibly emulsions. Copyright 2000 Academic Press.

Journal Article↗
PubMed2005

The microcanonical thermodynamics of finite systems: the microscopic origin of condensation and phase separations, and the conditions for heat flow from lower to higher temperatures.

Microcanonical thermodynamics [D. H. E. Gross, Microcanonical Thermodynamics, Phase Transitions in "Small" Systems (World Scientific, Singapore, 2001)] allows the application of statistical mechanics both to finite and even small systems and also to the largest, self-gravitating ones. However, one must reconsider the fundamental principles of statistical mechanics especially its key quantity, entropy. Whereas in conventional thermostatistics, the homogeneity and extensivity of the system and the concavity of its entropy are central conditions, these fail for the systems considered here. For example, at phase separation, the entropy S(E) is necessarily convex to make e(S(E)-E/T) bimodal in E. Particularly, as inhomogeneities and surface effects cannot be scaled away, one must be careful with the standard arguments of splitting a system into two subsystems, or bringing two systems into thermal contact with energy or particle exchange. Not only the volume part of the entropy must be considered; the addition of any other external constraint [A. Wehrl, Rev. Mod. Phys. 50, 221 (1978)], such as a dividing surface, or the enforcement of gradients of the energy or particle profile, reduce the entropy. As will be shown here, when removing such constraints in regions of a negative heat capacity, the system may even relax under a flow of heat (energy) against a temperature slope. Thus the Clausius formulation of the second law: "Heat always flows from hot to cold," can be violated. Temperature is not a necessary or fundamental control parameter of thermostatistics. However, the second law is still satisfied and the total Boltzmann entropy increases. In the final sections of this paper, the general microscopic mechanism leading to condensation and to the convexity of the microcanonical entropy at phase separation is sketched. Also the microscopic conditions for the existence (or nonexistence) of a critical end point of the phase separation are discussed. This is explained for the liquid-gas and the solid-liquid transition.

Journal Article↗
PubMed2003

The potential of organic (electrospray- and atmospheric pressure chemical ionisation) mass spectrometric techniques coupled to liquid-phase separation for speciation analysis.

The use of mass spectrometry based on atmospheric pressure ionisation techniques (atmospheric pressure chemical ionisation, APCI, and electrospray ionisation, ESI) for speciation analysis is reviewed with emphasis on the literature published in and after 1999. This report accounts for the increasing interest that atmospheric pressure ionisation techniques, and in particular ESI, have found in the past years for qualitative and quantitative speciation analysis. In contrast to element-selective detectors, organic mass spectrometric techniques provide information on the intact metal species which can be used for the identification of unknown species (particularly with MS-MS detection) or the confirmation of the actual presence of species in a given sample. Due to the complexity of real samples, it is inevitable in all but the simplest cases to couple atmospheric pressure MS detection to a separation technique. Separation in the liquid phase (capillary electrophoresis or liquid chromatography in reversed phase, ion chromatographic or size-exclusion mode) is particularly suitable since the available techniques cover a very wide range of analyte polarities and molecular mass. Moreover, derivatisation can normally be avoided in liquid-phase separation. Particularly in complex environmental or biological samples, separation in one dimension is not sufficient for obtaining adequate resolution for all relevant species. In this case, multi-dimensional separation, based on orthogonal separation techniques, has proven successful. ESI-MS is also often used in parallel with inductively coupled plasma MS detection. This review is structured in two parts. In the first, the fundamentals of atmospheric pressure ionisation techniques are briefly reviewed. The second part of the review discusses recent applications including redox species, use of ESI-MS for structural elucidation of metal complexes, characterisation and quantification of small organometallic species with relevance to environment, health and food. Particular attention is given to the characterisation of biomolecules and metalloproteins (metallothioneins and phytochelatins) and to the investigation of the interaction of metals and biomolecules. Particularly in the latter field, ESI-MS is the ideal technique due to the softness of the ionisation process which allows to assume that the detected gas-phase ions are a true representation of the ions or ion-biomolecule complexes prevalent in solution. It is particularly this field, important to biochemistry, physiology and medical chemistry, where we can expect significant developments also in the future.

Atmospheric Pressure↗
PubMed2005

Reaction-induced phase separation of pseudo-interpenetrating polymer networks in polydisperse polymer blends: a simulation study.

We develop a minimal model for the process of reaction-induced phase separation in a polydisperse polymer blend. During the reaction, one component undergoes polymerization, leading to phase separation via spinodal decomposition. The effect that changing the final degree of polymerization has on the phase-separation process is studied. Finally an elastic energy term is included mimicking the cross-linking process and the generation of a semi-interpenetrating polymer network. We show that the scaling of the dominant lengthscale with time varies according to the reaction conditions.

Journal Article↗
PubMed2003

Phase-separation transition in one-dimensional driven models.

A class of models of two-species driven diffusive systems which is shown to exhibit phase separation in d=1 dimensions is introduced. Unlike previously studied models exhibiting similar phenomena, here the relative density of the two species is fluctuating within the macroscopic domain of the phase separtated state. The nature of the phase transition from the homogeneous to the phase-separated state is discussed in view of a recently introduced criterion for phase separation in one-dimensional driven systems.

Journal Article↗
PubMed1990

Separation processes in biotechnology. Aqueous two-phase separations.

Aqueous two-phase systems are useful for separation of a wide range of water-compatible substances (from peptides to cells). The selectivity of the separation normally increases with the size of the partitioned molecules or particles. The partition and separation capacity can be influenced in a number of ways, including electric charge, hydrophobicity, or specific ligand binding. Because of the simpleness in operation and high capacity, aqueous two-phase systems are well suited for large-scale purification of biomaterials such as enzymes and other specific proteins.

Animals↗
PubMed2006

Selectivity in reversed-phase separations Influence of the stationary phase.

The selectivity difference between 15 different stationary phases was measured using a large number of analytes at 2 or 3 different pH values (3, 7 and 10) with acetonitrile and methanol as the mobile phase modifiers. The packings discussed include standard C(8) and C(18) packings, packings with embedded polar groups, a phenyl packing, a pentafluoro-phenyl packing, an adamantylethyl packing and others. The major selectivity differences observed are discussed in detail. Specific effects such as pi-pi interactions on phenyl packings or hydrogen-bond interactions on phases with embedded polar groups are confirmed.

Acetonitriles↗
PubMed1985

Phase separation induced in gelatin-base coacervation systems by addition of water-soluble nonionic polymers II: effect of molecular weight.

Phase separation, induced in aqueous solutions of gelatin or gelatin-acacia by adding polyethylene oxide (PEO) or polyethylene glycol (PEG) of different molecular weights, was examined. The minimum concentration (Cp) of PEO or PEG required to cause phase separation decreased with an increase in the molecular weight (M2) of the polymer. The dependence of Cp on M2 for a complex coacervation (gelatin-acacia-water) system was larger than for a simple coacervation (gelatin-water) system, in which Cp was approximately proportional to M2-1/2. Elemental analyses indicated that coacervates induced in gelatin-water systems by the addition of PEO (or PEG) did not contain PEO (or PEG); therefore, phase separation may be due to incompatibility.

Chemistry, Pharmaceutical↗
PubMed2004

Crystal-like pattern formation in polymerization-induced phase separation.

A unique domain structure was found in liquid-liquid phase separation induced by radical polymerization of 4-chlorostyrene monomer in the presence of random copolymer poly(dimethylsiloxane-co-diphenylsiloxane). Droplets with a narrow size distribution were generated by phase separation, and these droplets hardly coalesced by collisions. With the growth of droplet size, droplets gradually filled the space and spontaneously arranged themselves in a regular array like a crystal. The mechanism of regular array formation was discussed based on the large difference in viscoelastic properties between two segregating components.

Journal Article↗
PubMedDate not supplied

Rosin coacervate microcapsules: effect of solvent on phase separation of rosin.

The effect of various solvent-non-solvent pairs on phase separation of rosin was studied visually and microscopically. The type of phase separated was found to be a function of viscosity of the solution rather than the dielectric constant of the solvent. Triangular phase diagrams were constructed and optimum coacervation conditions were determined. Of all the solvents tested, only ethanol and acetone yielded a coacervate phase.

Capsules↗