Quantitative prediction of phase diagrams for polymer partitioning in aqueous two-phase systems

Published polymer distribution data for aqueous poly(ethylene glycol)/dextran mixtures have been reassessed to illustrate the feasibility of their quantitative characterization in terms of the Flory-Huggins theory of polymer thermodynamics. Phase diagrams predicted by this characterization procedure provide better descriptions of the experimental data than those based on an earlier, oversimplified treatment in similar terms. (C) 2003 Wiley Periodicals, Inc.

Pseudo-ternary phase diagrams of aqueous mixtures of Quil A, cholesterol and phospholipid prepared by the lipid-film hydration method

Pseudo-ternary phase diagrams of the polar lipids Quil A, cholesterol (Chol) and phosphatidylcholine (PC) in aqueous mixtures prepared by the lipid film hydration method (where dried lipid film of phospholipids and cholesterol are hydrated by an aqueous solution of Quil A) were investigated in terms of the types of particulate structures formed therein. Negative staining transmission electron microscopy and polarized light microscopy were used to characterize the colloidal and coarse dispersed particles present in the systems. Pseudo-ternary phase diagrams were established for lipid mixtures hydrated in water and in Tris buffer (pH 7.4). The effect of equilibration time was also studied with respect to systems hydrated in water where the samples were stored for 2 months at 4degreesC. Depending on the mass ratio of Quil A, Chol and PC in the systems, various colloidal particles including ISCOM matrices, liposomes, ring-like micelles and worm-like micelles were observed. Other colloidal particles were also observed as minor structures in the presence of these predominant colloids including helices, layered structures and lamellae (hexagonal pattern of ring-like micelles). In terms of the conditions which appeared to promote the formation of ISCOM matrices, the area of the phase diagrams associated with systems containing these structures increased in the order: hydrated in water/short equilibration period < hydrated in buffer/short equilibration period < hydrated in water/prolonged equilibration period. ISCOM matrices appeared to form over time from samples, which initially contained a high concentration of ring-like micelles suggesting that these colloidal structures may be precursors to ISCOM matrix formation. Helices were also frequently found in samples containing ISCOM matrices as a minor colloidal structure. Equilibration time and presence of buffer salts also promoted the formation of liposomes in systems not containing Quil A. These parameters however, did not appear to significantly affect the occurrence and predominance of other structures present in the pseudo-binary systems containing Quil A. Pseudo-ternary phase diagrams of PC, Chol and Quil A are important to identify combinations which will produce different colloidal structures, particularly ISCOM matrices, by the method of lipid film hydration. Colloidal structures comprising these three components are readily prepared by hydration of dried lipid films and may have application in vaccine delivery where the functionality of ISCOMs has clearly been demonstrated. (C) 2003 Elsevier B.V. All rights reserved.

A comparison of pseudo-ternary diagrams of aqueous mixtures of Quil A, cholesterol and phospholipid prepared by lipid-film hydration and dialysis

Pseudo-ternary diagrams for Quil A, phospholipid (phosphatidylcholine (PC) or phosphatidylethanolamine (PE)) and cholesterol were established in order to identify combinations that result in the formation of immune-stimulating complex (ISCOM) matrices and other colloidal structures produced by these three components in aqueous systems following lipid-film hydration or dialysis (methods that can be used to produce ISCOMs). In addition, the effect of equilibration time (1 month at 4degreesC) on the structures formed by the various combinations of the three components was investigated. Depending on the ratio of Quil A, cholesterol and phospholipid, different colloidal particles, including ISCOM matrices, liposomes and ring-like micelles, were found irrespective of the preparation method used. In contrast, worm-like micelles were only observed in systems prepared by lipid-film hydration. For samples prepared by dialysis, ISCOM matrices were predominantly found near the Quil A apex of the pseudo-ternary diagram (> 50% Quil A). On the other hand, for samples prepared by lipid-film hydration, ISCOM matrices were predominantly found near the phospholipid apex of the pseudo-ternary diagram (> 50% phospholipid). The regions in the pseudo-ternary diagrams in which ISCOM matrices were observed increased following an extended equilibration time, particularly for samples prepared by lipid-film hydration. Differences were also observed between pseudoternary diagrams prepared using either PE or PC as phospholipids.

Automated layout of small lattices using layer diagrams

Good quality concept lattice drawings are required to effectively communicate logical structure in Formal Concept Analysis. Data analysis frameworks such as the Toscana System use manually arranged concept lattices to avoid the problem of automatically producing high quality lattices. This limits Toscana systems to a finite number of concept lattices that have been prepared a priori. To extend the use of formal concept analysis, automated techniques are required that can produce high quality concept lattice drawings on demand. This paper proposes and evaluates an adaption of layer diagrams to improve automated lattice drawing. © Springer-Verlag Berlin Heidelberg 2006.

Mean-field phase diagrams of imbalanced Fermi gases near a Feshbach resonance

We propose phase diagrams for an imbalanced (unequal number of atoms or Fermi surface in two pairing hyperfine states) gas of atomic fermions near a broad Feshbach resonance using mean-field theory. Particularly, in the plane of interaction and polarization we determine the region for a mixed phase composed of normal and superfluid components. We compare our prediction of phase boundaries with the recent measurement and find a good qualitative agreement.