title: The aqueous solubility and thermal stability of α-lipoic acid are enhanced by cyclodextrin.
abstract: 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, β-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-β-CD enhancing solubility the most. The thermal stability of α-lipoic acid in the solid state was improved by the addition of G2-β-CD(®), a commercial product of 6-O-α-maltosyl-β-CD. The thermal stability of α-lipoic acid was also improved by the addition of β-CD. Analysis by differential scanning calorimetry showed that G2-β-CD(®), a mixture of maltosyl-β-CDs, and β-CD efficiently formed complexes with α-lipoic acid. These results suggest that the sizes and shapes of these β-CD compounds are compatible with complexation with α-lipoic acid. Moreover, both the formation of an aqueous complex with G2-β-CD(®) and an insoluble complex with β-CD increased the thermal stability of α-lipoic acid.
authors.affiliation: Carbohydrate Research Laboratory, Ensuiko Sugar Refining Co., Ltd., Japan. htakahashi@ensuiko.co.jp
authors.forename: Hideki
authors.initials: H
authors.lastname: Takahashi
authors.forename: Yuri
authors.initials: Y
authors.lastname: Bungo
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Mikuni
mesh_terms: D002152:Calorimetry, Differential Scanning; D003505:Cyclodextrins / Q000737:chemistry*; D004355:Drug Stability; D011208:Powders; D012995:Solubility; D013696:Temperature; D008063:Thioctic Acid / Q000737:chemistry*; D014867:Water / Q000737:chemistry*
chemical_list: D003505:Cyclodextrins; D011208:Powders; D014867:Water; D008063:Thioctic Acid