Studies on curcumin and curcuminoids XXXI.: Symmetric and asymmetric curcuminoids:: Stability, activity and complexation with cyclodextrin

A series of curcummoids, including curcumin, were studied with the main focus on their solubility, phase-distribution, hydrolytic stability and photochemical stability in cyclodextrin (CD) solutions. Their radical scavenging properties were also briefly studied. All the investigated derivatives were more stable towards hydrolytic degradation in CD solutions than curcumin, and the general order of the stabilising effect was HP beta CD > M beta CD >> HP gamma CD. In contrast, the photochemical studies showed that curcumin is generally more stable than its derivatives. Solubility and phase-distribution studies showed that curcuminoids with side groups on the phenyl moiety have higher affinity for the HP gamma CD than for the beta CDs and that the relative affinity of the larger HP gamma CD cavity increases with the curcuminoid molecule size. The radical scavenging studies showed that curcumin is more active than the derivatives investigated and that the free phenolic hydroxyl group may be essential for the scavenging properties. This study also indicates that the two halves of the symmetric curcumin molecule act as two separate units and scavenge one radical each. (c) 2007 Elsevier B.V. All rights reserved.