Fluorinated amphiphiles

LS. In the LS phase the molecules are oriented normal to the surface in a hexagonal unit cell. It is identified with the hexatic smectic BH phase. Chains can rotate and have axial symmetry due to their lack of tilt. Cai and Rice developed a density functional model for the tilting transition between the L2 and LS phases [202]. Calculations with this model show that amphiphile-surface interactions play an important role in determining the tilt their conclusions support the lack of tilt found in fluorinated amphiphiles [203]. 

M.P. Krafft, Fluorocarbons and fluorinated amphiphiles in drug delivery and biomedical research, Adv. Drug Deliv. Rev. 47 (2001) 209-228. 

M.P. Krafft, J.G. Riess, Highly fluorinated amphiphiles and colloidal systems, and their applications in the biomedical field—A contribution, Biochimie 80 (1998) 489-514. 

The extensive studies of the behavior of mixed monolayers or bilayers of di-acetylenic lipids and other amphiphiles parallel to some degree the studies of dienoyl-substituted amphiphiles. Since the dienoyl lipids do not contain a rigid diacetylenic group in the middle of the hydrophobic chains, they tend to be miscible with other lipids over a wide range of temperatures and compositions. In order to decrease the lipid miscibility of certain dienoyl amphiphiles, Ringsdorf and coworkers utilized the well-known insolubility of hydrocarbons and fluorocarbons. Thus two amphiphiles were prepared, one with hydrocarbon chains and the other with fluorocarbon chains, in order to reduce their ability to mix with one another in the bilayer. Of course it is necessary to demonstrate that the lipids form a mixed lipid bilayer rather than independent structures. Elbert et al. used freeze fracture electron microscopy to demonstrate that a molar mixture of 95% DM PC and 5% of a fluorinated amphiphile formed phase-separated mixed bilayers [39]. Electron micrographs showed extensive regions of the ripple phase (Pb phase) of the DM PC and occasional smooth patches that were attributed to the fluorinated lipid. In some instances it is possible to... 

Vierling, P., Santaella, C. and Greiner, J. (2001) Highly fluorinated amphiphiles as drug and gene carrier and delivery systems. J. Fluorine Chem., 107, 337-354. 

Fluorocarbons and fluorinated amphiphiles have found a variety of applications in materials science and medicine [1-5]. As many of these applications involve colloidal systems stabilized by a monolayer of fluorinated amphiphiles, it is essential to understand the structure and properties of these interfacial films. Such knowledge can provide improved control over the engineering and properties of highly fluorinated colloids and interfaces [6]. 

Surface micelles of fluorinated amphiphiles have potential as templates for the elaboration of metallic nanodot arrays. Hexagonal arrays of gold and silver nanodots, a few nM in size, have been observed by AFM to form when a thin layer of metal was deposited through vacuum evaporation on a silicon wafer covered with hemimicelles of the F8H16 diblock (E. Charrault, P. Muller, M. Maaloum, M.P. Krafft, C. Petit, P. Petit, unpublished). 

Giulieri, F., and Krafft, M. R (2003), Tubular microstructures made from nonchiral single-chain fluorinated amphiphiles Impact of the structure of the hydrophobic chain on the rolling-up of bilayer membrane, J. Coll. Interf. Sci., 258, 335-344. 

Figure 19 General structure for designed fluorinated amphiphilic oxadiazoles.

Key words Vesicle - fibril - cryo-TEM - small-angle X-ray scattering -fluorinated amphiphile... 

Microemulsions of surfactants in SCFs have emerged as effective supercritical solvent systems for the preparation and processing of materials. Microemulsions are particularly useful in the case of SCFs such as CO2 that are environmentally benign but of relatively low solvent strength. However, because most conventional surfactants contain no C02-philic moieties, microemulsions in CO2 require special surfactants such as fluorinated amphiphilic molecules (229-235). Other commonly used SCFs are simple hydrocarbons, which are compatible with conventional surfactants such as AOT. A unique advantage of SCF-based microemulsions is that properties of the microemulsions may be varied via changes in the pressure and temperature of the SCF (Figure 24) (236-244). 

Meinert et al. [104-106] found that already small quantities [1 or 2% (w/v)] of partially fluorinated alkanes, C, F2 ,+ iC H2h+i, stabilize perfluorodecalin-Pluronic F68 emulsions. Riess et al. [130] deseribed a binary emulsifier system, consisting of a nonfluorinated surfactant in conjunction with a partially fluorinated alkene. Riess et al. [130] named the fluorinated amphiphile a dowel," suggesting that its fluorophilic end adsorbs in the fluorocarbon surface and its lipophilic end penetrates the lipophilic part of the egg-yolk phospholipid. The dowel, C8Fi7CH=CHCsHi7, increased the stability of a perfluorooctyl bromide (PFOB)-egg-yolk lipid emulsion stability considerably. The droplet size (0.25, m) remained constant over 9 months, even at 40 C. In the absence of the dowel, the droplet size more than doubled at 25 C to 0.49 jum. 

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