Mechanism study of selected phenolic compounds determination using β-cyclodextrin-coated CdSe/ZnS quantum dots

Abstract

β-Cyclodextrin (βCD)-coated CdSe/ZnS quantum dots (QDs), provide a sensitive method for the determination of phenolic compounds. The current study aimed to explain the mechanisms involved in photoluminescence quenching of CdSe/ZnS QDs, during the determination of quercetin and gallic acid, and select derivatives thereof. Quercetin, quercetin glycosides, gallic acid and gallate esters, were investigated to understand how the glycoside moiety in glycosides and the hydrocarbon chain in esters, affect the interactions of the investigated polyphenols with βCD-coated QDs. The phenomenon of βCD-coated CdSe/ZnS photoluminescence quenching, is caused by the effective formation of host-guest inclusion complexes between polyphenols and βCD. The presence of the glycoside moiety in the quercetin molecule reduced the effectiveness of the complex formation, while, in contrast, the efficiency of complexation increased with increasing hydrocarbon chain length of the gallate ester molecule. QD photoluminescence quenching may be a consequence of the proximity between the interacting phenolic compounds with the QD surface, rather than βCDs peeling off from the QD surface, resulting in structural destabilization. From the thermodynamic parameters, it was concluded that the formation of the complexes is based both on the van der Waals interactions forces and hydrophobic interactions between guest and host molecules. Ionic interactions may also play an important role in the effectiveness of polyphenol-βCD inclusion complex formation. In order to obtain QDs with long-term stability, there is a need to increase the zeta potential value of the QD surface. Recognition of the above-described mechanisms, should enable the optimization of existing methods and the development of new applications of βCD-coated CdSe/ZnS QDs, such as determination of octyl gallate in foodstuffs.