PROPERTIES OF LIPID VESICLES 115 Table I Aqueous Volume Capture and Mean Vesicle Diameters of Three Types of Sarcosinate Vesicles Sarcosinate Mean diameter pH (microns) (ml/g) Aqueous volume (ml/mMol) N-lauroyl 3.67 0.600 4.16 1.12 N-cocoyl 3.24 0.466 4.08 1.14 N-oleoyl 3.54 0.399 2.55 0.89 Table II Aqueous Volume Capture and Mean Vesicle Diameters of Three Types of Sarcosinate/Cholesterol Vesicles Sarcosinate Mean diameter pH (microns) f (ml/g) Aqueous volume (ml/mMol) N-lauroyl 3.67 0.209 4.41 1.19 N-cocoyl 3.24 0.339 4.41 1.23 N-oleoyl 3.54 0.255 2.19 0.76 Table III Oil Capture and Mean Vesicle Diameters of Three Types of Sarcosinate and Sarcosinate/Cholesterol Vesicles Oil uptake Sarcosinate (ml/g) (ml/mMol) N-lauroyl 12.5 3.38 N-lauroyl/cholesterol 16.2 4.37 N-cocoyl 7.1 2.00 N-cocoyl/cholesterol 10.3 2.88 N-oleoyl 7.1 2.49 N-oleoyl/cholesterol 13.2 4.62 0.75, the vesicles are multilamellar with typical birefringence patterns. At a ratio of 0.75 the N-lauroyl sarcosinate gives a gel phase that gives rise to multilamellar vesicles upon mixing with water. Important features of sarcosinate/cholesterol vesicles (3/1 M/M) formed using delonized water as aqueous phase are given in Table II. Oil uptake by sarcosinate and sarcosinate/ cholesterol vesicles (3/1 M/M), formed using deionized water as aqueous phase, are given in Table III. Lipid vesicles made of N-acyl sarcosinates as sole amphiphiles (or sarcosinate/cholesterol combinations) are stable at neutral and acidic pH values. At pH 8 or higher, they disintegrate as the amphiphiles go into solution. The cholesterol of sarcosinate/ cholesterol vesicles precipitates under these circumstances. Vesicles made of mixtures of N-acyl sarcosinates and nonionic amphiphiles are less pH-sensitive than vesicles made only of N-acyl sarcosinates. Figure 1 shows the freeze fracture appearance of N-cocoyl

116 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Figure 1. Freeze fracture electron micrograph of N-cocoyl sarcosinate vesicles laden with Dior fragrance 37 D. Most of the fields show 300-500-nm vesicles with two membranes. An occasional large multilamellar vesicle (inset) is observed, revealing greater structural detail. Magnification 45,000X.