RESUMEN
We investigated the effects of various cyclodextrins (CDs) on the aqueous solubility and thermal stability of α-lipoic acid, a compound with low water solubility. α-CD, ß-CD, and γ-CD had little effect on the aqueous solubility of α-lipoic acid. In contrast, 6-O-α-maltosyl-CDs increased it in a concentration-dependent manner, 6-O-α-maltosyl-ß-CD enhancing solubility the most. The thermal stability of α-lipoic acid in the solid state was improved by the addition of G2-ß-CD(®), a commercial product of 6-O-α-maltosyl-ß-CD. The thermal stability of α-lipoic acid was also improved by the addition of ß-CD. Analysis by differential scanning calorimetry showed that G2-ß-CD(®), a mixture of maltosyl-ß-CDs, and ß-CD efficiently formed complexes with α-lipoic acid. These results suggest that the sizes and shapes of these ß-CD compounds are compatible with complexation with α-lipoic acid. Moreover, both the formation of an aqueous complex with G2-ß-CD(®) and an insoluble complex with ß-CD increased the thermal stability of α-lipoic acid.