Encapsulation effects on the structure and tautomeric distribution of curcumin in the β-cyclodextrin cavity: an ion mobility study

Abstract

Encapsulated 1 : 1 and 1 : 2 complexes of the bioactive compound curcumin in the β-cyclodextrin (βCD) cavity have been investigated by drift tube ion mobility mass spectrometry (DTIMS) in combination with the collision induced dissociation (CID) method. The bioavailability of curcumin, which depends on its solubility in an aqueous medium, is enhanced significantly as a result of encapsulation in highly water-soluble βCD. The mass spectrometry data reveal that the abundance of the 1 : 2 complex is nearly twice compared to that of the 1 : 1 complex. The preference of the tautomeric distribution of curcumin is altered significantly upon encapsulation in favor of the folded diketo tautomer over the extended keto–enol tautomeric form, and the effect is observed in the case of both 1 : 1 and 1 : 2 complexes of curcumin with βCD. The binding interaction of curcumin with βCD was theoretically computed using the AutoDock 4 software package. Comparison of the experimentally measured collision cross-section (CCS) values from the DTIMS method with those predicted theoretically by the MobCal program showed an overestimation of approximately 6–7%, which is within the accepted uncertainty range (∼5–7%) for the N₂-parameterized MobCal code. By elucidating the conformational behavior of the curcumin–βCD complex and the preferred tautomeric form of curcumin, this research provides valuable insights into the complex's behavior, with potential applications in drug delivery and therapeutics.