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.