j. Soc. Cosmet. Chem., 46, 29-38 (January/February 1995) $olubilization of vitamin E acetate in a lameliar liquid crystal GUO RONG, STIG E. FRIBERG, and ANDRe-JEAN BRIN, Center for Advanced Materials Processing and Department of Chemistry, Clarkson University, Potsd•am, NY 13699-5814 (G.R., S.E.F.), and Laboratoires Dr. N. G. Payot, 7 Boulevard d'Osny-Cergy St. Christophe, F-95808 Cergy Pontoise, France (A.-J.B.) Received November 3, 1994. Synopsis Vitamin E acetate was solubilized into a lamellar liquid crystal formed by water and triethanol/oleic acid in a 35/65 weight ratio, and the geometrical dimensions of the lamellar liquid crystal were determined using low-angle x-ray diffraction. The solubilization was huge, with maximum values reaching 63% by weight. The presence of the vitamin E acetate did not change the dimension of the amphiphilic layer of the liquid crystal, but strongly reduced the water penetration into the amphiphilic layer at small solubilization levels. INTRODUCTION Vitamin E has a significant interest for cosmetic formulations due to its anti-oxidative action. It is well known that the UV radiation from the solar spectrum damages the skin by forming free radicals (1), highly reactive molecules causing lasting damage to the skin structure by lipid peroxidation and oxidative modification of proteins and DNA. The observation that skin cancer is one of the most frequent forms of human cancers (2) is an excellent illustration of the perils related to sun radiation exposure. Vitamin E absorbs UV radiation (3), also forming radicals but of a less-reactive kind: the vitamin structure stabilizes the unpaired electron structure, and the radical molecule is comparably harmless to the skin. Unfortunately, the epidermis contains lower concen- trations of vitamin E than most other tissues in the human body, and it is essential to find a suitable vehicle to enhance and replenish the vitamin lost by UV-radiation exposure. Vitamin E itself is an oil, and its direct application is far from satisfactory from a cosmetic point of view, because of its tackiness and oily appearance. This problem is also experienced for products in which the vitamin is emulsified in water to more than a few 29

30 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS percent. With this article we present a liquid crystalline vehicle that solubilizes vitamin E to an order of magnitude higher than the values obtained in traditional emulsion systems. EXPERIMENTAL MATERIALS Materials used were triethanolamine (TEA, Fisher 99.3%, Fairlawn, NJ), oleic acid (OLA, Fisher, Fairlawn, NJ), vitamin E acetate (VE, ot-tocopherol acetate, Sigma, St. Louis, MO), and water (doubly distilled). Determination of lamellar liquid crystalline phase. The lameliar liquid crystalline phase of the TEA-OLA-water system was obtained by mixing various ratios of water with TEA and titration with OLA, and by mixing various ratios of TEA with OLA and titration with water. The boundary lines were checked by optical microscopy with polarized light and by low-angle x-ray diffractometry. The maximum amount of vitamin E in the liquid crystal of the TEA-OLA-water system was determined by addition of vitamin E to the liquid crystal systems with different composition, by observation under polarized mi- croscopy, and by small-angle x-ray diffractometry. LOW-ANGLE X-RAY DIFFRACTION Low-angle x-ray diffraction measurements were obtained by a Kiessig low-angle camera from Richard Seifert, Germany. Ni-filtered Cu radiation was used, and the reflections were determined by a Tennelec Position Sensitive detectory system (Model PSD-100). RESULTS The lameIlar liquid crystalline region in the TEA-OLA-water system are shown in Figure 1, demonstrating the tolerance of the liquid crystal to water contents reaching WATER TEA OLA Figure 1. The region of the lameliar liquid crystal in the system water, oleic acid (OLA), and triethanol- amine (TEA). The lines show compositions to which vitamin E acetate was added.