Long-chain lecithin

Bian, J. and Roberts, M. F. (1990). Phase separation in short-chain lecithin/gel state long-chain lecithin aggregated3iochemistry, 29, 7928-7935. 

Phospholipase Ai activity is routinely measured by titrimetry in a pH-stat using substrate emulsions of whole egg yolk [31], purified long-chain lecithin in the presence of detergents to facilitate formation of micelles [321 and radiolabeled... 

Figure 10 (Left) The rates of hydrolysis of emulsified long-chain triglycerides by pancreatic lipase. The highest rate occurs with triglycerides emulsified with gum arabic (no lecithin). All the other curves represent hydrolysis rates of triglycerides emulsified with long-chain lecithin. There is a long lag period and then a slight hydrolysis in the absence of additives. With added bile salts, the lag period is abolished, but the hydrolysis rates ate still low. Both colipase and colipase plus bile salts accelerate the hydrolytic rates. (Right) Concerted action of pancreatic lipase and phospholipase. Addition of phospholipase A2 hydrolyzes the phospholipid emulsifier (as indicated by the lysolecithin release), stops the lag phase, and initiates an accelerated triglyceride hydrolysis. (From Ref. 35.)...

Four enzymes, required for the lecithin biosynthesis are reconstituted in a soybeanPC proteoliposome. Short- and long-chain lecithin can be synthesized within such liposomes, that were prepared by the detergent depletion method. 

The conditions for surfactants to be useful to form Hquid crystals exist when the cross-sectional areas of the polar group and the hydrocarbon chain are similar. This means that double-chain surfactants are eminently suited, and lecithin (qv) is a natural choice. Combiaations of a monochain ionic surfactant with a long-chain carboxyHc acid or alcohol yield lamellar Hquid crystals at low concentrations, but suffer the disadvantage of the alcohol being too soluble ia the oil phase. A combination of long-chain carboxyHc acid plus an amine of equal chain length suffers less from this problem because of extensive ionisa tion of both amphiphiles. 

Quaternary ammonium compounds (QACs Chapter 10) such as cetrimide, and also the bisbiguanide, chlorhexidine, are notoriously prone to promote clumping. A non-ionic surface-active agent of the type formed by condensing ethylene oxide with a long-chain fatty acid such as Cirrasol ALN-WF (ICI Ltd), formerly known as Lubrol W, together with lecithin, added to the diluting fluid has been used to overcome this effect. 

Among the most abundant components of the cysteine + ribose + lecithin reaction mixture were the 2-pentylpyridine and two long-chain alkyl substituted thiophenes 2-pentyl- and 2-hexylthiophenes [31,32], together with a related compound with molecular formula and... 

The effect of various snake venoms on surface films of lecithin is to remove one of the long-chain fatty-acid groups from the molecule, causing a considerable fall in surface potential 3 this reaction is much slowed by compression of the film as the result of compression is to remove the double bonds in the oleyl group (the one split off) of the lecithin from the surface, it is possible that the lecithinase, the enzyme which splits off the oleyl group, has a molecular structure which fits both the end group and the double bond in the lecithin. 

A surfactant molecule is an amphiphile, which means it has a hydrophilic (water-soluble) moiety and a hydrophobic (water-insoluble) moiety separable by a mathematical surface. The hydrophobic tails of the most common surfactants are hydrocarbons. Fluorocarbon and perfluorocarbon tails are, however, not unusual. Because of the hydrophobic tail, a surfactant resists forming a molecular solution in water. The molecules will tend to migrate to any water-vapor interface available or, at sufficiently high concentration, the surfactant molecules will spontaneously aggregate into association colloids, i.e., into micelles or liquid crystals. Because of the hydrophilic head, a surfactant (with a hydrocarbon tail) will behave similarly when placed in oil or when put in solution with oil and water mixtures. Some common surfactants are sodium or potassium salts of long-chained fatty acids (soaps), sodium ethyl sulfates and sulfonates (detergents), alkyl polyethoxy alcohols, alkyl ammonium halides, and lecithins or phospholipids. 

These functional characteristics are primarily derived from the chemical structures of lecithin s major phospholipids (Figure 1) (7). Phospholipid molecules contain two long-chain fatty acids esterified to glycerol, as well as a phosphodiester bonding a choline, inositol, or ethanolamine group. A phospholipid s fatty acid end is nonpolar and thereby lipophilic (or fat loving). Conversely, the phosphodiester, with the above-mentioned constiments, is zwitterionic (or dipolar), which... 

Bile salts readily form mixed micelles with lipid-like molecules such as lecithins or fatty acids. These mixed micelles are structurally very different from the simple micelles and generally have a much greater solubilizing capacity for hydrophobic molecules, both biological and synthetic. The solubility of DDT, a non-polar, water insoluble molecule, for example, in bile salt micellar solution can be increased to a far greater extent by the addition of unsaturated long chain fatty acids, probably because of mixed micelle formation. 

This figure shows the Influence of the hydrocarbon chain lengths on the phase behaviour of phosphatidylethanolamines (PEs) and lecithins (PCs). If the hydrocarbon chains are relatively short, monolayers are in the gaseous (G) or liquid-expanded (LE) state, while for sufficiently long chains condensed monolayers are formed. These monolayers are already in the coexistence state between gaseous (G) and condensed phase at a surface pressure of about zero and their x(A) isotherms exhibit no plateau region at accessible temperatures. In two cases increase of the surface pressure above a particular value k results in a first order phase transi-... 

N. E. Gabriel, N.V. Agman, and M. F. Roberts. Enzymatic-hydrolysis of short-chain lecithin long-chain phospholipid unilamellar vesicles sensitivity of phospholipases to matrix phase state. Biochemistry, 1987, 26, 7409-7418. 

The monolayers chosen included cephalins and lecithins as examples of molecules expected to have a high polarizability normal to the interface (9, 26). Long chain sulfate and quaternary ammonium ions were studied as examples of monolayers with diffuse ionic double layers. Other experiments were made with protein films, with a long chain /5-alanine, and with monolayers of equimolar mixtures of long chain sulfates and quaternary ammonium ions. The various results can be explained by the effects illustrated below for long chain sulfates and lecithin. 

Fat-soluble vitamins such as retinol and )3-carotene are readily dissolved in mixed lipid-bile salt micelles in vitro. Retinol is approximately 10 times more readily dissolved in such micelles than /3-carotene [105]. It is likely that these two substances occupy different regions of the micelle. The difference in solubility, therefore, may reflect the limited capacity of the nonpolar core of the micelle for the relatively bulky /3-carotene molecule. Retinol, on the other hand, may occupy a more hydrophilic region of the micelle. In a mixed oil/micellar system, a-tocopherol distributes between the two phases, its concentration in the micellar phase being enhanced by expansion of the micelles with monoglycerides and lecithin of long-chain fatty acids. However, lipids containing medium-chain fatty acids do not expand the micelles as effectively as their long-chain counterparts such that there is less solubilization of a-tocopherol in the micellar phase [106]. 

FinaUy, certain long-chain molecules are able to bind fuUerenes by micelle formation and to finely disperse them in a medium. The examples reported for this kind of interaction mostly use surfactants like Triton X-100 or lecithin. The hydro-phobic fullerene is incorporated into the miceUe, partly in its center, but partly also in its periphery. Among other effects, this interaction leads to the solubility of such adducts in water. The embedding in long-chain, amphiphilic molecular units is also used to prepare artificial membranes holding fuUerenes. 

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