Lecithin amphiphilic head group

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

Amphiphiles with two chains per charged head group, such as didodecyldi-methylammonium cation, dicetylphosphate anion, and the lecithin of biomembranes tend to form bilayers, not micelles, in which the chains are presumably more ordered than those in simple micelles. Such layers can exist as flat sheets, as in multilamellar structures (21) or as the curved surface of a spherical micelle (22). N.m.r. evidence... 

The methods of preparing lipid vesicles are well known [2,5,9]. Vesicles are made predominantly from amphiphiles, a special class of surface-active molecules, which are characterized by having a hydrophilic (water soluble) and a hydrophobic (water insoluble) group on the same molecule. A typical vesicle-forming molecule, such as lecithin (see Fig. 7), has two hydrocarbon chains, also called hydrophobic or nonpolar tails, attached to a hydrophilic group, often named the polar head. In general, most of these molecules are not soluble in water however, instead of solutions they form colloidal dispersions [15]. 

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