Computational and spectroscopic analysis of the Quercetin encapsulation in (2HP-β-CD)2 and (2,6Me-β-CD)2 complexes

Abstract

Quercetin protects against many diseases due to its radical scavenging and anti-inflammatory properties. However, due to its poor bioavailability numerous types of nanocarriers have been evolved to increase quercetin solubility and to design tissue-specific delivery systems. Here, we study the entrapment of quercetin(QUE) in two dimeric assemblies formed by 2HP-β-CD and 2,6Me-β-CD, employing DFT calculations, NMR and fluorescent spectroscopy. Via NMR and fluorescent spectroscopy, it was revealed that the QUE:CDs stoichiometry for optimal complex formation follows a 1:2 pattern. DFT indicated that although both dimeric assemblies of 2HP-β-CD and 2,6Me-β-CD, as well as their encapsulation quercetin complexes are stable, the former dimer and the QUE@2HP-β-CD2 complex demonstrate the highest level of stability. The absorption spectrum of QUE in CD and CD2 was calculated. Encapsulation influences it, resulting in red and blue shifts, and in differences in the intensities. Only, the dimeric assemblies affect the electron density of QUE resulting in major peaks at about 250 nm, which are charge transfer (CT) or partially CT excitations. Finally, for the encapsulated QUE in CDs, the calculated T1→S0 vertical de-excitation is about 570 nm in the single CDs and about 800 nm in the dimeric complexes, making these complexes potential candidates for PDT.