Double-chain amphiphiles

The conditions for surfactants to be useful to form Hquid crystals exist when the cross-sectional areas of the polar group and the hydrocarbon chain are similar. This means that double-chain surfactants are eminently suited, and lecithin (qv) is a natural choice. Combiaations of a monochain ionic surfactant with a long-chain carboxyHc acid or alcohol yield lamellar Hquid crystals at low concentrations, but suffer the disadvantage of the alcohol being too soluble ia the oil phase. A combination of long-chain carboxyHc acid plus an amine of equal chain length suffers less from this problem because of extensive ionisa tion of both amphiphiles. 

Okane et al. measured the CMC values of a-sulfonated fatty acid higher alcohol esters. These molecules can be regarded as double-chain amphiphiles, but the CMC values are about three to six orders of magnitude larger than expected for double-chain amphiphiles that can spontaneously form vesicles in water [60]. 

Structural characterizations of the immobilized bilayer assemblies are essential for the molecular design of the functional materials. On the bases of the systematic crystallographic investigation of single crystals of double-chain ammonium amphiphiles [9], Okuyama wrote a computer simulation program for the calculation of bilayer structures in cast bilayer films and bilayer thicknesses estimated from the repeating period in the X-ray diffraction data have been exclusively used for structural discussions [10,11]. 

The effect characteristic of a multi-chain hydrophobe, that is, increase in the cmc and simultaneous decrease in the cloud point, appears to be inconsistent with the well-known HLB concept in surfactants. Tanford has pointed out that based on geometric considerations of micellar shape and size, amphiphilic molecules having a double-chain hydrophobe tend to form a bilayer micelle more highly packed rather than those of single-chain types ( ). In fact, a higher homologue of a,a -dialkylglyceryl polyoxyethylene monoether has been found to form a stable vesicle or lamellar micelle (9 ). Probably, the multi-chain type nonionics listed in... 

Inorganics can also be synthesized and used as templates. Thus, controlled siloxane networks were formed when dispersions of alkoxysilanes (such as (MeO)3SiMe) are mixed with the suitable template matrixes. Ultrafine particles of metal oxides can be used as starting materials for the formation of metal oxide films. For instance, a mixture of a double-chained ammonium amphiphile and an aqueous solution of aluminum oxide particles (diameter about 10 100 nm) gives a multilayered aluminum oxide film when calcinated at over 300°C. 

Spontaneous aggregation of lipids — double chain amphiphiles — in aqueous medium (smectic phase). Hydrophobic core of long alkyl chains (lamellar orientation) is covered by hydrophilic headgroups (see Figs. 2, 15). 

In addition to the chain length, the hydrocarbon chain unsaturation also plays a very important role. This is clearly shown by the data on cationic PCs, which demonstrate drastic transfection increase with increase of the number of double bonds per lipid from 0 to 2 (Fig. 13a). Studies on double chained pyridinium compounds SAINT (Synthetic Amphiphile INTeraction) (Fig. 17, inset) have shown that, while elongation of the saturated alkyl chains from 06 0/06 0 to 08 0/08 0 resulted in a reduction by a factor of about two in the transfection efficiency, introduction of double bonds reversed this effect and resulted in very strong increase of the transfection efficiency (Fig. 17). When substituting only one of the saturated 08 0 alkyl chains for unsaturated 08 1 chain, the transfection efficiency increased by an order of magnitude, while the diunsaturated compound,... 

It was generally found that double chain ammonium glutamic acid amphiphiles of the general formula 2Cn-Glu-CmN+ (15) typically form typical bilayer vesicles above their phase transition temperature.118 It is interesting to refer to the compound 2Ci2-Glu-CnN+ (15b, n = 12)111,119 in which the predominant superstructures were flexible filaments with... 

Jaeger et al. described [46] some novel double-chain vesicle-forming cleav-able amphipiles which were synthesized via ion-pairing of two oppositely charged head groups. These amphiphiles formed giant vesicles which cleave at the labile carbon-nitrogen double bond around pH 3. 

Y. Ishikawa, H. Kuwahara, T. Kunitake, Self-Assembly of BUayers from Double-Chain Fluorocarbon Amphiphiles in Aprotic Organic Solvents Thermodynamic Origin and Generalization of the Bilayer Assembly , J. Am. Chem. Soc., 116,5579 (1994)... 

As already discussed, the assumption that the surface area Oo is not much affected by doubling the number of chains is supported by the observation that these areas are independent of chain length, and have much the same values for both single chained and double chained amphiphiles. This is also expected on theoretical grounds for hydrocarbon chains in the fluid state. 

Reversible polymerization or cross-linking by oxidative coupling of hydrosulfides to sulfides is often employed in biological protein chemistry. This principle can be also realized in membrane assemblies, where two terminal SH-groups are introduced into double-chain amphiphiles" (Scheme 2.15). Vesicles made from such amphiphiles form (on average) 20-mers with hydrogen peroxide and are depolymerized by 1-octanethiol. 

Electron microscopy provides perfect pictures of vacuum collapsed vesicle membranes after negative staining with heavy metal salts. BLMs appear usually as collapsed balls, MLMs often as flat disks (see Figure 4.29). There is no requirement for double-chain amphiphiles in order to form vesicles. The same single-chain amphiphiles which form micelles also form vesicles if their charge is neutralized. This was practised, for example, via the protonation of soaps or through addition of an amphiphilic counterion. In both cases, fatty acids function perfectly well in the form of vesicles. 

The vesicle-forming ethylenediaminediacetic acid derivative 10 complexes metal ions (e.g. Cu " ) from the aqueous phase. Since ftietal ions cannot generally penetrate hydrophobic vesicle membranes, literally any redox-active ions can be fixed to the inner and/or outer membrane surfaces. Cationic metallovesicles were also obtained from the double chain amphiphile 11 synthe-... 

Certain pathological cells produce excessive amounts of a particular enzyme, e.g. neuroblastoma/acetylcholinesterase. If such an enzyme is capable of breaking open specially designed vesicles which encapsulate a cytotoxic drug, then cell selective therapeutic activity can be achieved. The double-chain amphiphile 23 forms vesicles and incorporates an acetylcholine-like head group which was readily hydrolyzed by acetylcholinesterase (AcE). The primary alcohol then ejected one of the two tails and the remaining single chain amphiphile destroyed the bilayer membrane-bound fluorescent dyes were set free within seconds. ... 

Double-chain ammonium amphiphiles based on glutamic acid of the general formula 2C -Glu-C N" (65) typically give typical bilayer vesicles by dispersion in water with sonication above the phase transition temperature (Chart 11). The dispersion of 2C,2-L-G1u-C,iN (65b, n = showed, a few hours after... 

More recent studies showed that liposomes from POPC (a double-chain amphiphile, 1-palmitoyl-2-oleoyl-phosphatidylcholine) could also be utilized for such experiments. In these studies, the liposomes containing the enzyme were made semipermeable by adding sodium cholate, a well-described detergent. By using this technique, liposomes containing the appropriate enzyme (and template if... 

However, using double-chain ionic surfactants, e.g. sodium-bis-ethylhexylsulfo-succinate (AOT) [9, 67] and didodecyl dimethyl ammonium bromide (DDAB) [68], no co-surfactant is necessary to time the mean curvature of the amphiphilic film from positive to negative. In the following the quaternary (pseudo-ternary) system H20/NaCl (A)-n-decane (B)-AOT (D) will be discussed to show the main features of ionic microemulsions. Subsequently, the knowledge gained for alkylpolyglucoside micro emulsions (see Section 1.2.3) will be applied to understand the complex behaviour of five component ionic mixtures. 

PLGA has been widely known to show a specific conformational change between an a-helix and a random coil induced by varying pH, ion strength, and so on. We have prepared a double-chain amphiphile containing a PLGA segment (1L) and have described its peculiar conformational behavior on water. 

---