Crystalline transition temperature

Crystalline polyimide powders, 304 Crystalline transition temperature. See Melting temperature (Tm) Crystallization rate, for processing semicrystalline polymers, 44 CTE. See Coefficient of thermal expansion (CTE)... 

The chloroform solution of lipids (Solution A) is placed in a 50-mL round-bottomed spherical Quick-fit flask. Following evaporation of the solvent in a rotary evaporator at about 37°C, a thin lipid film is formed on the walls of the flask. The film is flushed for about 60 seconds with oxygen-free nitrogen (N2) to ensure complete solvent removal and to replace air. Two milliliters of distilled water and a few glass beads are added into the flask, the stopper is replaced, and the flask shaken vigorously by hand or mechanically until the lipid film has been transformed into a milky suspension. This process is carried out above the liquid-crystalline transition temperature (7/) of the phospholipid component of liposomes (> 7/) by prewarming the water... 

DNA arranges into rectangular superlattice in the low-temperature gel phase of saturated cationic lipids [83, 84]. This is evidenced by two or three diffuse reflections in addition to the set of lamellar reflections these are attributed to DNA ordering both within the layer and across the lipid bilayers, from one DNA layer to another. These reflections index on a centered rectangular lattice. Noteworthy, DNA does not affect the gel-liquid crystalline transition temperatures of the lipoplexes [16, 19, 84]. This transition is associated with loss of the DNA inter-lamellar correlation. 

Calamitic compounds which exhibit a smectic and/or nematic phase usually consist of a relatively rigid central core containing co-linear six-membered rings, either aromatic rings, such as 1,4-disubstituted-phenylene, 2,5-disubstituted-pyridine, 2,5-disubstituted-pyrimidine, 3,6-disubstituted-pyridazine, and alicyc-lic rings, such as /ra j-l,4-disubstituted-cyclohexane, 1,4-disubstituted-bicy-clo[2.2.2]octane, 2,5-disubstituted-dioxane. Heteroaromatic rings tend to lead to the formation of smectic phases rather than the nematic phase unless combined with a polar terminal function, such as a cyano group. The dependence of the liquid crystalline transition temperatures on the nature of... 

An obvious hypothesis is that this unusual membrane lipid composition is related directly to membrane function in some way. Within the restricted area of lipid bilayers, lipid composition is known to be an important determinant of physical properties. There are several prominent examples. First, the temperature at which the hydrocarbon chains melt when assembled in bilayers (the gel-to-liquid-crystalline transition temperature, marks an abrupt change in many of the physical properties of such bilayer systems for example, water permeability through such bilayers increases by several orders of magnitude above the transition. Second, the presence of cholesterol within bilayers composed of amphipathic lipids has a profound effect on lipid motion, mechanical properties (such as resistance to shear), and permeability to water. 

Recently, a molecular dynamics study of the phospholipid DLPE was reported by Damodaran et al. using a united atom model. The model was built from the crystal structure of DLPE reported by Elder et al. The fully hydrated DLPE bilayer has an interlamellar water layer of 5 A. The bilayer was solvated by 553 SPCE waters ( 11 water molecules/lipid) in the head group region. This lipid has a gel-to-liquid-crystalline transition temperature of... 

Poly(tetrafluoroethylene) exhibits a melting point of 327°C and a glass-transition temperature of 120°C. The helix of the fluorine atoms, which occurs below GG = 19°C, changes at this crystalline-crystalline transition temperature into a ISv helix. The helix of the chain, however, remains the same above and below 19°C, e.g., 13. Above torsional oscillations begin to occur about the helical backbone. A glass-glass transition observed at Tgg — — 120°C has not as yet been given a molecular interpretation. 

In contrast with the results obtained with the apoHBD-diCl4 liposomes complexes (cf Table 1), with the diCl4 substituted membranes, no HBD activity is detected at temperatures below 24 C (Fig. 6) which is near the gel-to-liquid crystalline transition temperature of diCl4 (the difference could be due to the effect to the protein). HBD activity appeared at 26°C and increased sharply with temperature the activation energy being about 7.4 kcal/mol. 

FIG. 2 Plots of ( ) the solid ctystaUine-soM crystalline and (O) solid crystalline-liquid crystalline transition temperatures and ( ) the temperature of isotropization as a function of the total number of C atoms, 2n, in molecules of symmetrical alkylammonium alkyl sulfate. 

Polyquinolines having directly bonded quinoline units in the 6-positions and connected in the 2-positions by -phenylene units (eg. 5) are rigid rods that are highly crystalline, having crystalline transition temperatures at 500 C or above.These polymers are soluble only in the polymerization medium... 

Vesicles form spontaneously from extended sheets when phospholipids or surfactants are dissolved in water, and heated above the gel-to-liquid crystalline transition temperature. Bergstrom and Eriksson (5) suggested that the free energy required to form a spherical bilayer from sheets is made up of two contributions, i.e. an energy associated with bending the monolayers and the work required to stretch the bilayer, with the latter being determined by the planar bilayer tension. A major... 

First of all, biochemists studied the process in model systems, employing lipid vesicles. It has been recognized for some time that such vesicles can be induced to fuse when incubated in the region of their gel to liquid-crystalline transition temperature. Furthermore, it was also noted that Ca addition would induce fusion in phosphatidylserine-containing systems possibly by causing local crystalline points for fusion. The role of Ca in many (but not all) natural fusion events led to a great deal of interest in this phenomenon. 

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