Lipophilic tails

According to the colloid scientist Winsor, surfactants are defined as compounds which possess in the same molecule distinct regions of hydrophilic and lipophilic character. For example, in the oleate ion there is an alkyl chain that is basically hydrophobic (lipophilic tail) and a COO" headgroup that is hydrophilic (lipo-phobic). Being amphiphilic in nature, surfactants have the ability to modify the interface between various phases [66]. Their effects on the interface are the result of their ability to orient themselves in accordance with the polarities of the two opposing phases. The polar part can be expected to be oriented towards the more polar (hydrophilic, aqueous) phase, whereas the nonpolar tails should direct towards the nonpolar (lipophilic, oil) phase. 

The application of similar strategies of rigidifying and optimizing the lipophilic tail in the aminoalcohol field has led to a number of aminoalcohol analogs... 

The dyes used for probing lipid membranes consist of a fluorophore with a long lipophilic tail. The lipophilic tail inserts itself into the membrane thus locating the fluorophore label on the membrane. These products are used as lipid labels and in cell tracking as part of biophysical studies. There are two main classes of fluorophore, aminostyryls and indocarbocyanines. The most widely used indocarbocya-nine is the 18-carbon derivative of Cy3 known as dil, (3.72). 

Inhaled salmeterol has a pharmacological half-life in excess of 12 hours, much longer than either albuterol or terbutaline. The likely basis for this long half-hfe is that the long lipophilic tail of salmeterol promotes retention of the molecule in the cell membrane. Its long duration of action makes salmeterol particularly suitable for prophylactic use, such as in preventing nocturnal symptoms of asthma. Because of its relatively slow onset of action, salmeterol should not be used to treat acute symptoms. 

Several laboratories have described systems by which synthetic linear peptide chains self-assemble into desirable secondary and tertiary structures. One self-assembly approach has been the creation of a peptide-amphiphile, whereby a peptide head group has the propensity to form a distinct structural element, while a lipophilic tail serves to align the peptide strands and induce secondary and tertiary structure formation, as well as providing a hydrophobic surface for self-association and/or interaction with other surfaces. The preparation of a dialkyl ester tail first involves the acid-catalyzed condensation of H-Glu-OH with the appropriate fatty acid alcohol to form the dialkyl ester of H-Glu-OH a typical example is shown in Scheme 7. The assembly of peptide-amphiphiles with mono- and dialkyl ester tails is shown in Scheme 8. A series of studies have demonstrated that triple-helical and a-helical protein-like molecular architecture is stabilized in the peptide-amphiphile 44,63-65 ... 

An additional modelling study was undertaken to quantify these findings [41], To this end, the already geometry optimized complex of carboxylate and truncated thioperamide (18) was used as a template. This fixed template was used to construct the different benzyl analogues shown in Table 4, by attachment of the distinct lipophilic tails. In this additional modelling study, only the geometry of these lipophilic tails were optimized using the... 

Most cationic lipids are composed of either two lipophilic tails or a steroid moiety, typically based on cholesterol. The classic method for steroidyl incorporation involves the reaction of a steroidyloxycarbonyl halide (e.g. cholesteryloxycar-bonyl chloride (2)) with primary amines from the linking moiety, a method used for the synthesis of most cholesterol-based cationic lipids including DC-Chol (3) [68, 72] (Fig. 2b) and BGTC (7) [73] (Fig. 3a). 

For nonionic surfactants, an optimization of the process was achieved by using a similar approach to the so-called Cohesive Energy Ratio (CER) concept developed by Beerbower and Hill for the stability of classical emulsions (H). Its basic assumption is that the partial solubility parameters of oil and emulsifier lipophilic tail and of water and hydrophilic head are perfectly matched. Thus, the Vinsor cohesive energy ratio Ro, which determines the nature and the stability of an emulsion, is directly related to the emulsifier HliB (hydrophile-lipophile balance) by... 

---