LG 106W AND INCLUSION COMPLEXES 233 I i i 20000 - •, 15000 • 10ooo • • ---'} •--•• ..... {A) 5000 (B) (c) (,) I I , 10.0 20.0 30.0 20( ø ) Figure 4. Powder X-ray diffraction patterns of LG106W-HP-[•-CyD system. (A) LG106W alone (B) HP-[•-CyD alone (C) complex of LG106W with HP-[•-CyD (D) physical mixture of LG106W and HP-[3-CyD. derivatives. Based on the solubility diagrams, the following results could be attained: In the case of •-CyD and HP-•-CyD, the solubility of LG106W increased linearly as a function of CyD concentrations, and the solubility curves can be classified as type AL. In these diagrams, due to the limited solubility of •-CyD, it was hard to measure the solubility increase with enough range compared to the other CyDs. The apparent 1:1 stability constants, Kc, were calculated from the initial straight line portion of the solubility diagrams. The stability constants are listed in Table I. On the other hand, the 25. 20. 1õ. 10. Concentration of CyDs ( x 10-3M) Figure 5. Phase solubility diagrams of LG106XV with three types of CyDs in 0.1 M phosphate buffer (pH 7.0) at 25 øC. O, [3-CyD O, HP-[3-CyD •r, DM-[3-CyD.

234 JOURNAL OF COSMETIC SCIENCE Table I Stability Constant of LG106W Complexes in Phosphate Buffer (pH 7.0) at 25øC CyDs K•:•(M -•) K•:2(M -•) [3-CyD 3,897 HP-[3-CyD 3,964 DM-[3-CyD 6,186 2.0 solubility of LG106W with DM-[3-CyD showed a different diagram, where the solu- bility curve can be classified as Ap. The ascending curvature of DM-[3-CyD in the figure was quantitatively analyzed according to the optimization technique previously pub- lished in another paper (12) to obtain the stability constant of high-order complexes. It is important to determine the Kc value with accuracy, because this parameter is a useful index for estimating the changes in physicochemical properties of the guest molecule upon inclusion. The Kc values increased in the order of DM-[3 HP-[3 [3-CyD, and they generally formed a 1:1 complex. From the above results, we chose HP-[3-CyD, one of the most widely used ones, as a model CyD and then continued with the following experiment. Figure 6 shows the time course of recovery rate of LG106W in free or HP-[3-CyD complex form with the temperature (A) and the pH (B). The stability of LG106W, especially at 50øC, was improved by complexation with HP-[3-CyD. From the results of pH stability (Figure 6B), it was apparent that the stability of LG106W was improved by complexation with HP-[3-CyD in the pH range employed. Skin care cosmetics in markets usually contain water as a main component, and so it is important to maintain the stability of the active compound in aqueous solution and to search for tools for improving the stability. From this point of view, HP-[3-CyD might be one of the lOO• r..D 60 40 • 20 (A) 40' 20' 0 0 4'0 ='0 a'0 io ø0 4'0 i0 10 i0 Time (Days) Time (Days) Figure 6. Effect of HP-[3-CyD on the stability of LG106W in 1,3-butylene glycol solution at different temperatures (A): 25øC, O 40øC, W] 50øC, V and at different pH (B): 4.5, O 6.5, [-] 8.5, V. The closed and open symbols show the material alone and the HP-[3-CyD complex, respectively.