Types of Amphiphile

Much of the early work on amphiphiles was undertaken on soaps and lipids based on fatty acids, and the corresponding non-systematic chemical names of these parent compounds and their derivatives are still commonly encountered. For convenience, Table 4.1 lists the systematic and trivial names of fatty acids, along with their structures. The names of derivatives are based on these for example sodium dodecyl sulphate is (still ) sometimes referred to as sodium lauryl sulphate. Other non-systematic names also exist to cause further confusion For example, hexadecyl (Cie chain) compounds are often termed cetyl derivatives. The use of the term fatty here and elsewhere is used to indicate an alkyl chain with 12 or more carbon atoms, i.e. a hydrocarbon that forms fats. 

In the following, we give examples of typical amphiphiles. The term surfactant is used somewhat interchangeably with amphiphile, although surfactant is usually implied in this book to mean a man-made snbstance, as opposed to a biological lipid. This convention is not, however, nniversal. 

Number of C atoms Common name of acid Systematic name of acid Structure 

Sodium alkyl ether sulphate/ carboxylate/phosphate 

Typical nonionic surfactant structures are shown in Fig. 4.3, along with some common names. The hydrophilic group of nonionic surfactants is usually a polyether chain, and more rarely a polyhydroxyl chain. The hydrophobic tail is often simply an alkyl chain. The fatty alcohol ethoxylates (also known as polyoxyethylene glycol monoethers) are a particularly important class that is widely used and extensively studied. They are abbreviated to C ,E , where C stands for methyl and E for oxyethylene and the subscripts 

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Arpagaus, M., Richier, P., Berge, J.-B. and Toutant, J.-P. (1992) Acetylcholinesterases of the nematode Steinemema carpocapsae. Characterization of two types of amphiphilic forms differing in their mode of membrane association. European Journal of Biochemistry 207, 1101-1108. 

Two types of amphiphilic quaternary 3-pyridinium ketoximes (253a, b) with different positioning of the hydrophobic alkyl chain have been synthesized and tested as hydrolytic micellar catalysts. A considerable positive deviation from the expected first-order curve was observed in the absorbance vs time plot when p-nitrophenyl diphenyl phosphate (252 R = Ph) and p-nitrophenyl diethyl phosphate... 

The most simple type of amphiphile film or a polymer film would be a gaseous state. This film would consist of molecules that are at a sufficient distance apart from each other such that lateral adhesion (van der Waals forces) are negligible. However, there is sufficient interaction between the polar group and the subphase that the filmforming molecules cannot be easily lost into the gas phase, and the amphiphiles are almost insoluble in water (subphase). 

Several additional studies were carried out to obtain information about the precise behavior of the various components in the model system. The interplay between the manganese porphyrin and the rhodium cofactor was found to be crucial for an efficient catalytic performance of the whole assembly and, hence, their properties were studied in detail at different pH values in vesicle bilayers composed of various types of amphiphiles, viz. cationic (DODAC), anionic (DHP), and zwitterionic (DPPC) [30]. At pH values where the reduced rhodium species is expected to be present as Rh only, the rate of the reduction of 13 by formate increased in the series DPPC < DHP < DODAC, which is in line with an expected higher concentration of formate ions at the surface of the cationic vesicles. The reduction rates of 12 incorporated in the vesicle bilayers catalyzed by 13-formate increased in the same order, because formation of the Rh-formate complex is the rate-determining step in this reduction. When the rates of epoxidation of styrene were studied at pH 7, however, the relative rates were found to be reversed DODAC DPPC < DHP. Apparently, for epoxidation to occur, an efficient supply of protons to the vesicle surface is essential, probably for the step in which the Mn -02 complex breaks down into the active epoxidizing Mn =0 species and water. Using a-pinene as the substrate in the DHP-based system, a turnover number of 360 was observed, which is comparable to the turnover numbers observed for cytochrome P450 itself. 

Hyde et al. (24) found that the peak apparent viscosity of lamellar liquid crystal fell by about two orders of magnitude as alcohol chain length was reduced from 15 to five in water-alcohol-Teepol systems. However, the complete picture of how various types of amphiphilic compounds and their mixtures influence viscosity is not available. In particular, it is not known under what conditions fairly low viscosities of liquid crystals can be achieved although Hallstrom and Friberg (22) report viscosities of about 0.2 poise for some compositions in the water— monocaprylin-tricaprylin system. As indicated previously, low viscosities increase the possibilities for occurrence of hydrodynamic instabilities involving cellular convection. 

These examples emphasize that not only the macromolecular architecture plays an important role in the determination of the aggregate morphology, but that also interactions between block copolymer segments can strongly influence the final structure of the assemblies formed by these types of amphiphiles as seen for the smaller molecular amphi-philes. 

Kobayashi et al. [143-146] have synthesized several types of amphiphilic po-ly(2-oxazoline), 34 and its block cooligomers, 53-55, and applied them to soap-free emulsion copolymerization of styrene and vinyl acetate to produce mono-disperse, submicron-sized latex particles. They found that the particle size significantly depended on the type of macromonomer used and generally decreased with increasing the macromonomer concentration. 

A comparison of the yy values obtained for different types of film and different types of amphiphile molecules at various temperatures show that they do not vary much yy = 0.5 to... 

The lamellar phase exists by virtue of the fact that amphiphilic molecules assemble into such a phase under given circumstances. One challenge is to relate properties of such a mesophase to macroscopic relevant properties, which was addressed in Section 9.2. In Section 9.3 a scheme has been given that was introduced by Israe-lachvili, which is useful in describing why certain amphiphiles form certain meso-phases. This scheme has been successfully applied to many amphiphilic systems. One of the challenges addressed in Section 9.3 is to see how that scheme may be also applied to the assembly of proteins, as another type of amphiphile, in particular how to explain recently observed phenomena of protein fibrillisation. 

Monolayers and LB Films - Controllable Layered Assembly Some types of amphiphile form monolayer structures on the surface of water. These compressed monolayers can be transferred onto a sohd support in a layer-by-layer manner. This permits well-oriented multilayers to be created with defined numbers and sequences of layers. 

Many types of amphiphile can form these supramolecular structures (see Fig. 4.52). Most of these have the abiUty to form hydrogen bonds - hydrogen bond formation significantly increases the stabihty of a supramolecular assembly. The presence of a chiral center sometimes leads to the formation of ribbon-Uke structure and twisted fibers. 

Rod—coil copolymers are a type of amphiphile that can self-assemble into a variety of ordered nanostructures in a selective solvent.36-37-71 In solvents that selectively dissolve only coil blocks, rod—coil copolymers can form well-defined nanostructures with rod domain consisting of the insoluble block. This results in an increase of the relative volume fraction of the coil segments relative to the rod segments, which gives rise to various supramolecular structures. Particularly, poly(alkylene oxide) as the coil block of rod—coil molecule has additional advantages due to complexation capability with alkali metal cation, which can provide an application potential for solid polyelectrolytes and induce various supramolecular structures.72-75... 

Less successful was the use of achiral catalysts in chiral micelles. The induced enantioselectivity in the resulting a-amino acid derivatives was in all cases below 10% ee depending on the type of amphiphile [59]. Other asymmetric reac-... 

Fig. 1 Principle of self-organization of different types of amphiphiles (all the sketches are idealized).

O. The B -state /J-strnctnre therefore manifests a type of amphiphilicity (cationic character at each C, anionic character at O) that is expected to lead to enhanced donor-acceptor interactions in this spin set. 

New types of amphiphiles have recently been investigated which contain several ionic residues and also hydrophobic groups, and which may behave like an ionic micelle, but be monomeric, or aggregates of a relatively few monomers. One such material is hexapus (7) [125]. 

Polysiloxane-containing amphiphilic block copolymers have been prepared by different approaches. Coupling of an end-functionalized polydimethylsiloxane with a functionalized poly(ethylene oxide) led to the formation of PDMS- -PEO diblock copolymers. The sequential anionic ring-opening polymerization of tetramethyltetravinylcyclotetrasiloxane and hexamethylcyclotetrasiloxane resulted in the formation of a vinyl-substituted diblock copolymer, the vinyl groups of which could be modified by further reactions so as to import amphiphilic character. The phase behavior of short-chain PDMS-Z -PEO diblock copolymers revealed the preferred formation of lamellar phases by this type of amphiphile... 

The rates of these hydrolysis reactions (Nu = H2O) can be compared with nucleophilic substitution by bromide ions (Nu = Br ). A kinetic study has been made of these reactions in the presence of vesicles formed from synthetic amphiphiles, phospholipids, and mixtures of both types of amphiphiles. °° Particular attention was paid to the effect of addition of n-dodecyl-j8-glucoside (C Glu) as a mimic for glycohpids. Kinetic data were... 

The terms Y -shaped [109], tripodal , 1,1-double-tailed or peg-shaped [110] describe the molecular geometry of this type of amphiphile. At the hydrophilic head two hydrophobic tails are joined close together or even by a common link to the headgroup. Very famous examples for this molecular architecture are the biologically active phospholipids and sphingolipids [111]. Lipids occur in all biological cells and have common solubility properties generally they are water-insoluble, amphiphilic molecules... 

Hybrid Colloids Composed of Two Types of Amphiphilic Azo Polymers... 

Mesoporous organosilicates are synthesized using similar self-assembly approaches as pure silica meso-phases the main difference being the silicon-containing precursors that consist of bridged silsesquioxanes, (RO)3Si-R -Si(OR)3. Different types of amphiphile molecules, including cationic (alkyltrimethylammonium),... 

In this study, the authors investigate the living cationic polymerization of polar monomers in the presence of added bases to prepare living polymers of various properties and shapes. Based on the results, various types of amphiphilic copolymers are designed, and the stimuli-induced self-association of the products, such as thermosensitive physical gelation, is characterized. 

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