Amphiphilic lipopeptides

Maleimide-functionalized peptides react quantitatively with thiols and thus with di-fatty acid substituted thioglycerol, a fact which facilitates purification of the amphiphilic lipopeptide derivatives by simple precipitation as required for separation of the excess lipid building block (Scheme 16).t163 164 167l... 

Amphiphilic lipopeptides with a hydrophobic paraffinic chain containing from 12 to 18 carbon atoms and a hydrophilic peptidic chain exhibit lyotropic meso-phases and good emulsifying properties. The X-ray diffraction study of the mesophases and of dry lipopeptides showed the existence of three types of mesomorphic structures lamellar, cylindrical hexagonal and body-centred cubic. Two types of polymorphism were also identified one as a function of the length of the peptidic chain and the other as a function of the water content of the mesophases. The emulsifying properties of the lipopeptides in numerous pairs of immiscible liquids such as water/ hydrocarbons and water/base products of the cosmetic industry showed that small amounts of lipopeptides easily give three types of emulsions simple emulsions, miniemulsions and microemulsions. 

In order to obtain surfactemts able to emulsify base products for cosmetic industry without presenting adverse side effects to the skin and tissues, it was necessary to synthesize new surfactants. We have chosen as new surfactants the amphiphilic lipopeptides (5-6). 

Amphiphilic lipopeptides Cfj(AA)p are formed by a hydrophobic lipidic chain containing from 12 to 18 carbon atoms linked... 

A—B—A block copolymers assessment of samples, 23—24 construction of phase diagrams, 24 light-scattering measurements, 24—25 preparation of samples, 23 Adsorbed polymer layer around a sphere, self-similar picture, 32132 323 Ammonia—ammonium thiocyanate mixtures, solvents for cellulose, 157 Amphiphilic lipopeptides advantages, 117... 

Structure and Polymorphism of Lipopeptides. Amphiphilic lipopep-tldes Cjj(AA)p exhibit mesophases in aqueous solution for water concentrations smaller than about 60 %, The structure of the mesophases and of the dry lipopeptides obtained by evaporation of the mesophase water at a slow rate was determined by X-ray diffraction. Lipopeptides X-ray diagrams obtained are similar to those exhibited by classical amphiphiles (11). They have allowed us to establish the existence of three types of liquid-crystalline structures Isunel-lar, hexagonal and cubic. 

For non-ionic polysoaps the situation is quite different. Whereas in the case of oligoethyleneoxide head groups thermotropic mesophases seem to be absent [87, 121-124, 126, 231, 403, 409], polysoaps with liposaccharide [230,240, 300] surfactant fragments or with lipopeptide [244, 400-402] ones frequently show lamellar mesophases (e.g. of smectic A type) and even nematic ones (Fig. 39). It should be emphasized that the thermotropic mesophases here are not the result of mesogenic groups being present, but are the consequence of the amphiphilic character of the polysoaps and the resulting microphase separation. 

A wide variety of microorganisms also produce many kinds of surface-active lipoproteins or lipopeptides [63]. Mostly they exhibit the typical amphiphilic character and are generally extracellular. Representative of such surface-active lipopeptides is surfactin produced by Bacillus subtilis. It is composed of a heptapeptide cycle closed by a C14.15 P-hydroxy fatty acid that forms a lactone ring system (Fig. 15) [64]. This structure resembles those of iturins, another class of lipopeptides also produced by Bacillus subtilis [65]. 

In nature, there are many physiological structures and functions supported by amphiphilic molecules (namely, surfactants), such as lecithin, fatty acid, Upoamino acids, and lipopeptides. From this viewpoint, amino acid- and protein-based surfactants are logically one of the most important materials to be reviewed and developed. 

Natural phospholipids, sterols, glycopepetides, lipopeptides, polyether lipids, and sulfo-lipids, as well as synthetic amphiphiles and even certain silanes, can assemble to form bilayer lipid membranes (BLMs), which can be free or supported on mercury, gold, silver, graphite, clay, etc. [121-123]. Amphiphilic membrane proteins and soluble proteins mod-... 

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