Zwitterionic surfactant examples

An anionic surfactant is soluble only at a pH greater than tf pqf its ionizable group, whereas a cationic surfactant (e.g., primary, secondary, ortertiary amines) is soluble only at a pH less than its pKg. However, quaternary ammonium surfactants remain soluble at all pH values. Zwitterionic surfactants, for example, sulfobetaine surfactants, are neutral from pH 2 to 12, whereas some nonionic surfactants, for example, alkyldimethylamine oxides, are converted to cationic surfactants by protonation at acidic pH. 

Zwitterionic Surfactant A surfactant molecule whose polar group contains both negatively and positively charged groups. Example lauramidopropylbetaine, CnH23CONH(CH2)3N (CH3)2CH2COO" at neutral and alkaline solution pH. See also Amphoteric surfactant. 

The effect of temperature on double-chain zwitterionic surfactants and uncharged lipids is to increase v/al further beyond unity, allowing a range of aggregation states. For example, the diacyl lipid didodecyl phosphatidylethanolamine mixed with about 20% water exhibits "lamellar", cubic (V2) and reversed hexagonal (H2) phases upon heating [15]. This... 

Zwitterionic surfactants, also known as amphoteric surfactants, have both cationic and anionic centers present in the same molecule. Generally, their properties are highly dependent on the pH of the solution. The cationic part is based on primary, secondary, or tertiary amines or quaternary ammonium cations. The anionic part can be more variable and include sulfonates, as in CHAPS (3-[(3-Cholamidopropyl)dimethylammonio]-l-propanesulfonate). Other anionic groups are sultaines illustrated by cocamidopropyl hydroxysultaine. Examples of zwitterionic surfactants include betaines (such as cocamidopropyl betaine, dodecyl betaine, lauramidopropyl betaine and cocoamido-2-hydroxypropyl sulfobetaine) and phosphates (such as lecithin). 

To this point we have covered the first three of the four general classes of surfactants defined previously. To produce an example of the fourth class, an amphoteric or zwitterionic surfactant, it is only necessary to react dodecyl chloride with a difunctional material such as A,iV-dimethyl-3-aminopropane-1-sulfonic acid... 

As mentioned in Chapter 1, there can be thousands of molecules with polar heads and nonpolar tails, usable as surfactants. The applications are also many. Thus, the commercial anionic surfactants, recording about 50% of all surfactant production, are literally used all over the place shampoos, dishwashing detergents and washing powders are some common examples. Cationic surfactants likewise are used in hair-conditioners, fabric softeners, asphalt coating, corrosion inhibitor formulations for metal surfaces etc. The major applications of non-ionic surfactants are in the areas of food and drinks, as also pharmaceuticals and cosmetics. Amphoteric /zwitterionic surfactants have only limited applications one area is cosmetics, especially skin care products. 

Perfluorinated, cationic and zwitterionic surfactants are synthesized by the alkylation of perfluoroal-kanesulfonamides containing a secondary or tertiary amine function. Two examples illustrating the versatility of this approach are shown in Schemes 18.9 and 18.10. Perfluorooctanesulfonyl... 

N-alkylated perflnorooctanesnlfonamides such as PFOS (3-dimethylamino-propyl)-amide can be functionalized to yield cationic snrfactants (Scheme 18.10). For example, the methylation of this amide yields fluorinated qnatemary ammoninm surfactant that were manufactured by the 3M Company (Figure 18.2). These ammonium surfactants can be fnrther alkylated to yield cationic surfactants with both a flnorophobic and a lipophobic chain. Similarly, zwitterionic surfactants are synthesized by using chloroacetic acid, 3-propanesulfonic acid, or related compounds instead of methyl iodide as an alkylating agent. 

The three main types of surfactants are ionic, zwitterionic, and nonionic. Zwitteri-onic surfactants have anionic and cationic constituents. Examples of zwitterionic surfactants include betaines and dimethyl amine oxides. Ionic surfactants are generally classified as cationic if they are positively charged or anionic if they are negatively... 

The compounds triisobutyl (methyl) phosphonium tosylate (a) and trihexyl (tetradecyl) phosphonium bis 2,4,4-(trimethylpentyl)phosphinate (b) were synthesized (Fig. 4.14), and their surface-active properties studied.The polar compound (a) is water soluble and surface active, does not form micelles, but affects the micelliza-tion properties of ionic, nonionic, and zwitterionic surfactants more strongly than conventional electrolytes. The less polar compound (b) forms micelles and has very low aqueous solubility. Both compounds form mixed micelles with Triton X-100 nonionic surfactant in aqueous solution. Compound (a) replaces water to form microemulsions with isopropyl myristate as oil, stabilized by (b). Compound (a) showed a clear antitumor activity, for example, 5mg (a)mH in 0.9% NaCl solution caused 100% killing of Sarcoma-180 cell line in 1 h. More diluted solutions were still active 2.5 and 1 mg (a) mT caused 81 and 53% killing of the same cells, respectively. On the other hand, compound (b) was less active than (a) lOmg (b)mT in 0.9% NaCl solution caused 89% killing of Sarcoma-180 cell line in 2h. Note that the concentration of (b) employed was 33 times higher than its cmc (0.03 x 10" moll ). The efficiency of (a) with respect to (b) may be due to the fact that the former does not form micellar aggregates [89]. 

It is common to encounter a liquid-liquid miscibility gap having a lower critical temperature in nonionic surfactants. The phase boundary responsible for such behavior is termed a lower consolute boundary [62] Fig. 6 displays an example. A related kind of phase behavior that is inverted with respect to temperature has also been found, mostly among zwitterionic surfactants (Fig. 7). This boundary has an upper critical point and is termed an upper consolute boundary. Phase separation occurs on heating with the lower con-... 

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