Cholesteryl polyoxyethylene

Vineland, NJ) or over-the-counter cosmetic creams promoted for improved hydration (L Oreal, Paris and Dior, Paris). More recently, parenteral liposome formulations of amphotericin B, doxorubicin, and dau-norubicin have been approved and marketed (ABELCET, Elan, the Liposome Co., Inc, Princeton, NJ AmBisome and DaunoXome, Nexstar/Fujisawa, Deerfield Park, IL Amphotec and Doxil, Sequus/ Alza, Menlo Park, CA), with others on the horizon for applications in photodynamic therapy. Although the vast majority of liposome preparations are constructed from phospholipids, other nonphospholipid materials can be used either alone or in mixtures to form bilayer arrays. One such example is Amphotec, which utilizes sodium cholesteryl sulfate as the primary lipid. Other liposome forming materials may include but are not limited to fatty-acid compositions, ionized fatty acids, or fatty acyl amino acids, longchain fatty alcohols plus surfactants, ionized lysophospholipids or combinations, non-ionic or ionic surfactants and amphiphiles, alkyl maltosides, a-tocopherol esters, cholesterol esters, polyoxyethylene alkyl ethers, sorbitan alkyl esters, and polymerized phospholipid compositions. ° ... 

Kunieda s group reported numerous viscoelastic worm-like micellar systems in the salt-free condition when a lipophilic nonionic surfactant such as short hydrophilic chain poly(oxyethylene) alkyl ether, C EOni, or N-hydroxyethyl-N-methylaUcanolamide, NMEA-n, was added to the dilute micellar solution of hydrophilic cationic (dodecyltrimethylammonium bromide, DTAB and hexade-cyltrimethylammonium bromide, CTAB) [12-14], anionic (sodium dodecyl sulfate, SDS [15, 16], sodium dodecyl trioxyethylene sulfate, SDES [17], and Gemini-type [18]) or nonionic (sucrose alkanoates, C SE [9, 19], polyoxyethylene cholesteryl ethers, ChEO [10, 20], polyoxyethylene phytosterol, PhyEO [11, 21] and polyoxyethylene sorbitan monooleate, Tween-80 [22]) surfactants. The mechanism of formation of these worm-Hke stmctures and the resulting rheological behavior of micellar solutions is discussed in this section based in some actual published and unpublished results, but conclusions can qualitatively be extended to aU the systems studied by Kunieda s group. 

Maestro et al. (2004) [9] studied the R effect on the formation and disruption of the transient network formed by worm-hke micelles, using C12EO4 as the cosurfactant Oscillatory results at low and intermediate frequencies were fitted to the Maxwell model, as had been done in other pubUcations [9j. The obtained parameters Go and Tm are presented in Eigure 12.8 vs. ratio R. It can be observed that when R is increased. Go continuously grows, nearly reaching a plateau. On the other hand, Tm quickly increases up to the R for which the viscosity maximum is found, and then decreases up to phase separation. Kunieda s group found the same tendencies for other worm-hke micellar systems, like the water-polyoxyethylene cholesteryl ether Ch(EO) -Ci2(EO) systems [lOj. Eigure 12.9 shows some until... 

Figure 12 (a) Partial phase diagram of the water/polyoxyethylene cholesteryl ether(ChEOio)-Ci2E03 system, in the dilute region at 25 °C, (b) Variation of zero-shear... 

TABLE 4 Thermodynamic Parameters of Polyoxyethylene (30) Cholesterol CMC Values, Micellar Weight, and Aggregation Numbers of Polyoxyethylene Cholesteryl Ethers in Water... 

FIG. 2 Critical micelle concentration (CMQ of polyoxyethylene derivatives of (-0-) cholesterols (from [11,13]), ( ) lanolin alcohols [10], (x) phytosterol [16], ( ) cholesteryl carbonate [24], and (A) octylphenol [21]. Increasing the length of the polyoxyethylene chain causes a decrease in the CMC for the sterol derivatives, initially causes a decrease in the CMC (minimum at 15 oxyethylene imits) for the lanolin alcohols and then an increase, while for the octylphenol derivatives the CMC increases with increasing hydrophilicity. 

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