Cyclodextrins nanocavities effects on basic and acid fluorescence quenching of hydroxy-indoles

• The cyclodextrins effects on 5-hydroxy-indoles fluorescence emission in acid and alkaline quenching conditions were analyzed.
• In both media a decrease in the values of KQ was measured in the presence of cyclodextrins.
• A complete quenching inhibition produced by ionized cyclodextrins was determined for both substrates.
• This study is particularly important for analytical determinations in such media.
• The quenching protection by CDs and the quenching inhibition by ionized CDs is a general behavior of indole compounds.

The cyclodextrins effects on the serotonin (5HT) and 5-hydroxy-3-indolyl acetic acid (5HIA) fluorescence emission in acid and alkaline quenching conditions were analyzed. From Stern–Volmer plots, the quenching constants (KQ) were determined in the presence and absence of β-cyclodextrin (βCD) and hydroxypropyl-β-cyclodextrin (HPβCD). In both media a decrease in the values of KQ was observed in the presence of CDs, as compared with their absence. In acid media, the decrease was: 36–39% with βCD and 48–54% with HPβCD for 5HIA and 5HT, respectively. In basic media, with the neutral receptors, these values are 69–29% with βCD and 56–43% with HPβCD for 5HIA and 5HT, respectively. Moreover, a complete quenching inhibition produced by ionized cyclodextrins was determined for both substrates. The results showed a net protective effect due to the guest inclusion into the cyclodextrin nanocavity. This study is particularly important for analytical determinations in such media.