Lipid melting points

Finally, even when HC composition and cuticular transpiration are correlated, causation cannot be assumed. For example, higher cuticular water-loss rates in the desert ant, Pogonomyrmex barbatus, are correlated with a decrease in abundance of an n-alkane and an increase in a methylalkane (Figure 6.2 Johnson and Gibbs, 2004). This is exactly what one would expect if lipid melting points affect cuticular permeability, but this increase is also accompanied by a change in mating status. Mated, de-alate queens that have founded... 

In the solvent method the separation of the solubilised or dispersed material from the solvent phase can be explained by precipitation or phase change induced by solvent evaporation, addition of electrolyte, pH modification or heat treatment (Krochta and McHugh 1997). Such treatments can be adjusted to enhance film formation or specific properties. For composite emulsion-based films or coatings a lipid material and most likely a surfactant, is added to the solution, which is then heated above the lipid melting point and homogenised. The prepared solution is then applied on an appropriate support and the solvent evaporates. 

The melting points of even-numbered-carbon fatty acids increase with chain length and decrease according to unsaturation. A triacylglycerol containing three sam-rated fatty acids of 12 carbons or more is solid at body temperature, whereas if the fatty acid residues are 18 2, it is liquid to below 0 °C. In practice, natural acylglyc-erols contain a mixture of fatty acids tailored to suit their functional roles. The membrane lipids, which must be fluid at all environmental temperatures, are... 

The drug dissolved or dispersed in the melted lipid is poured into an aqueous emulsifier phase of the same temperature. By means of a rotor-stator homogenizer (e.g., an Ultra-Turrax), an o/w preemulsion is prepared and is then homogenized at high pressure and at a temperature at least 10°C above the melting point of the lipid. In most cases, nanoemulsion arises after only three to live homogenization cycles at 500 bar. Nanoparticles are formed by cooling the nanoemulsion to room temperature. 

From these descriptions, it is seen that the films may, under given experimental conditions, show three first-order transition states, such as (i) transition from the gaseous film to the liquid-expanded (Lex), (ii) transition from the liquid-expanded (Lex) to the liquid-condensed (Lco), and (iii) from Lex or Lco to the solid state if the temperature is below the transition temperature. The temperature above which no expanded state is observed has been found to be related to the melting point of the lipid monolayer. 

Lipofullerenes such as 35-37 self-assemble within lipid bilayers into rod-like structures of nanoscopic dimensions [61, 62]. These anisotropic superstructures may be important for future membrane technology. Significantly, lipofullerenes 35 and 37 have very low melting points, 22 and 67 °C (DSC, heating scan), respectively, with 35 being the first liquid fuUerene derivative at room temperature. 

Melting Points of Lipids The melting points of a series of 18-carbon fatty acids are stearic acid, 69.6 °C oleic acid, 13.4 °C linoleic acid, - 5 °C and linolenic acid, - 11 °C. (a) What structural aspect of these 18-carbon fatty acids... 

Membrane fluidity and life. In agreement with the known behavior of bilayers, the lipids of most membranes in all organisms are partially liquid at those temperatures suitable for life. Organisms have developed at least three distinct means of ensuring that membrane lipids remain liquid.145 (1) In our bodies (as well as in E. colt) the unsaturated fatty acids that are present lower the melting point. Mutants of E. coli that are unable to synthesize unsaturated fatty acids cannot live unless these materials are supplied in the medium.146 (2) In Bacillus subtilis, which contains no unsaturated fatty acids when grown at 37°C, and in other gram-positive bacteria, more than 70% of membrane... 

Draw the structure of the product you would obtain on hydrogenation of the lipid in Problem 24.72. What is its name Would the product have a higher or lower melting point than the original lipid Why ... 

The phase behavior of a synthetic lecithin, dipalmitoyllecithin, as analyzed by Chapman and co-workers (5), is diagrammed in Figure 3. The main features are the same as in the phase diagram of egg lecithin a mixture of numerous homologs. As a consequence of the variation in fatty acid chain length, the chain melting point is lowered which means that the critical temperature for formation of liquid crystalline phases is reduced. This temperature is about 42 °C for dipalmitoyllecithin, and, if the lamellar liquid crystal is cooled below this temperature, a so-called gel phase is formed. The hydrocarbon chains in the lipid bilayers of this phase are extended, and they can be regarded as crystalline. The gel phase and the transitions between ordered and disordered chains are considered separately. 

Antioxidants are tested for purity by melting point and TLC on heat-activated silica using solvent systems 1) chloroform, 2) chloroform/methanol, 19/1, 3) chloroform/methanol/acetic acid, 19/1/0.1. Antioxidants are added at 0.1% by weight of dispersed lipid. In a typical test, 50 ml of the lecithin microdispersion... 

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