Amphiphile structure

Luisi, P.L., Straub, B.E. (eds.) Reverse Micelles Biological and Technological Relevance of Amphiphilic Structures in Apolar Media, Plenum, 1984. 

A novel polymerized vesicular system for controlled release, which contains a cyclic a-alkoxyacrylate as the polymerizable group on the amphiphilic structure, has been developed. These lipids can be easily polymerized through a free radical process. It has been shown that polymerization improves the stabilities of the synthetic vesicles. In the aqueous system the cyclic acrylate group, which connects the polymerized chain and the amphiphilic structure, can be slowly hydrolyzed to separate the polymer chain and the vesicular system and generate a water-soluble biodegradable polymer. Furthermore, in order to retain the fluidity and to prepare the polymerized vesicles directly from prev lymerized lipids, a hydrophilic spacer has been introduced. 

In the discussion above it has been shown that the lipid can been polymerized through UV irradiation of its aqueous suspension. The polymerization of the system improves the stability of the synthetic liposomes. Since there is an acetal linkage introduced between the polymer chain and the amphiphilic structure, this linkage can be slowly hydrolyzed in aqueous systems to separate the polymer chain from the lipid. 

The procedure for the formation of vesicles from this prepolymerized lipid was similar to that for the monomeric lipid. However, the concentration of the lipid in this system was lower than in the case of the monomeric lipid. Also the time of sonication for this polymerized lipid was longer than that for the monomeric lipid because of the decreased freedom of motion of the amphiphilic structure in the polymerized system. The electron microscope pictures (Figure 7) show the formation of tiny and very homogeneous vesicles. 

The incorporation of dendritic moieties into amphiphilic structures is attractive as the dendritic component provides a unique opportunity to vary, in a controlled fashion, head group properties such as size and polarity, by simply changing the generation or the nature of its surface groups. Similarly, the length of the linear fragment can easily be modified to adjust properties. 

The selective functionalization of saccharose and sorbitol with fatty acids for the construction of a perfect amphiphilic structure cannot be realized in simple technical processes because of the polyfunctionality of the molecule. This is why the products offered on the market contain different amounts of mono-, di- and... 

Whereas the dendrofullerenes are water-soluble in an almost monomeric form, the amphiphilic structures 8-12 have a strong tendency to form aggregates in water as it is detected by line broadening in UV/Vis spectra. 

Langevin D (1984) In Luisi PL, Straube BE (eds) Reverse micelles biological and technological relevance of amphiphilic structure in a polar media. Plenum, New York, p 287... 

Similar structural studies have been made, for example, by Feigin and Lvov [36] using Y layers of barium behenate and also superlattices containing this material and other amphiphiles. Structural studies of Langmuir-BIodgett films have also been made by Belbeoch et al. [37],... 

Mesophases of supermolecular structure do not need a rigid mesogen in the constituent molecules. For many of these materials the cause of the liquid crystalline structure is an amphiphilic structure of the molecules. Different parts of the molecules are incompatible relative to each other and are kept in proximity only because of being linked by covalent chemical bonds. Some typical examples are certain block copolymers50 , soap micelles 51 and lipids52. The overall morphology of these substances is distinctly that of a mesophase, the constituent molecules may have, however, only little or no orientational order. The mesophase order is that of a molecular superstructure. 

Phospholipids are found in all living cells and typically constitute about half of the mass of animal cell plasma membranes (Cevc, 1992). The reason forthe variety of membrane lipids might simply be that these amphiphilic structures have in common the ability to arrange as bilayers in an aqueous environment (Paltauf and Hermetter, 1990). Thus, the use of endogenous phospholipids to form vesicles as drug carriers may have much less adverse effects in patients compared to synthetic drui carrier molecules. 

The successful synthesis of the biohybrid members of the family of amphiphiles, the giant amphiphiles, has also attracted the spotlight of fundamental sciences. The incorporation of biological molecules (proteins and enzymes) in to the amphiphilic structure mimics the self-assembly seen in Nature by amphiphilic proteins. Though enzymes and proteins have been extensively funtionalized in the past, the realization that they can express assembling properties similar to that of their molecular and polymeric counterparts offers new methods for the construction of functional biomimetic assemblages. The future for amphiphiles appears to be unlimited. 

In nature, polypeptides with amphiphilic structures are known to form transmembrane channels formed by an assembly of several helices, so as to present their polar faces inward and their apolar faces outward. In view of such behavior, the photochromic amphiphilic polypeptide was incorporated into a cationic bilayer membrane composed of dipalmitoyl phosphatidyl choline.11201 Fluorescence and microscopic measurements provided evidence that the polypeptide was able to form bundles of helical molecules analogous to their natural counterparts, which acted as transmembrane channels for K+ ions. Irradiation, and the consequent transacts isomerization of the azobenzene link, caused a bending of the molecular structure and a destabilization of the transmembrane bundles. Therefore, formation of ion permeable channels would be favored or inhibited depending on whether the azo moiety... 

Hydrocarbon surfactant liquids are promising candidates for C02 capture with the following advantages (1) The hydrocarbon surfactants are cheap and nontoxic (2) The solubility of C02 in surfactants can be readily tuned by tailoring the amphiphilic structure of polar head and nonpolar tail (3) As the hydrocarbon surfactants are nonvolatile, C02 can be desorbed without loss of the surfactants... 

It is commonly assumed that transfer processes can be modeled by bulk phase thermodynamics and that surface or interfacial effects are negligible. These assumptions may, in the case of partitioning into amphiphilic structures formed by micelles or bilayer membranes, not always be appropriate. These interfacial solvents have a large surface to volume ratio, similar to interfacial solvents used in reversed-phase liquid chromatography. The partitioning into such phases is the basis of the chromatographic separation. 

Finally, it is shown that non-linear amphiphilic structures show different aggregation behavior as compared to block copolymers. Graft copolymers with non-polar backbone polyelectrolyte side chains have a smaller tendency to form micelles than their block copolymer analogs which is attributed to the more facile stabilization of unimers by the sidechains. In contrast, unimolecular micelles are the only possibility for core-shell nanoparticles. Janus micelles, on the other hand, form unique non-centrosymmetrical micelles that have a strong tendency to form centrosymmetrical supermicelles. 

Artificial catalysts have also been incorporated into amphiphilic structures (Guler and Stupp, 2007). These catalysts were imidazolyl-functiona-lized peptides, which demonstrate a greater rate of 2,4-dinitrophenyl acetate hydrolysis when immobilized on the peptide amphiphile than the rate observed when the same enzyme is present in solution. Although the density of the enzymes on the fiber surface has not been established, the authors attribute the increase in enzymatic activity to the likely concentration of enzyme along the fiber surface, and this study illustrates one of the advantages of enzyme immobilization. 

Fig. 4 Stability and permeability of self-assembled amphiphilic structures. Amphiphilic molecules such as fatty acids having carbon chain lengths of 9 or more carbons form bilayer membranes when sufficiently concentrated, a Pure bilayers of ionized fatty acid are relatively unstable but become markedly more stable as long chain alcohols are added, b Dimensions of the amphiphile also play a role. Shorter chain amphiphiles (9-10 carbons) are less able to form bilayers, while those of intermediate chain length (12-14 carbons) produce stable bilayers that also are permeable to ionic and polar solutes. Longer chain lengths (16-18 carbons) produce bilayers that are increasingly less permeable to solutes [48]...

Figure 4. Proposed amphiphilic structure for a proteinaceous surfactant...

Surface-active substances — are electroactive or elec-troinactive substances capable to concentrate at the interfacial region between two phases. Surface-active substances accumulate at the electrode-electrolyte - interface due to -> adsorption on the electrode surface (see -> electrode surface area) or due to other sorts of chemical interactions with the electrode material (see - chemisorption) [i]. Surface-active substances capable to accumulate at the interface between two immiscible electrolyte solutions are frequently termed surfactants. Their surface activity derives from the amphiphilic structure (see amphiphilic compounds) of their molecules possessing hydrophilic and lipophilic moieties [ii]. 

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