Study on the inclusion interaction of ethyl violet with cyclodextrins by MWNTs/Nafion modified glassy carbon electrode

The interactions of ethyl violet (EV) with cyclodextrins (CDs) were investigated by Multi-wall carbon nanotubes/Nafion composite film modified glassy carbon electrode (MWNTs/Nafion/GCE). It was found that the MWNTs/Nafion composite film can effectively catalyze the electrode reaction of EV. The variation of the electrochemical behavior of EV upon the addition of CDs indicated the formation of the inclusion complexes of EV with beta-CD, heptakis (2,3,6-tri-O-methyl)-beta-CD (TM-beta-CD), heptakis (2,6-di-O-methyl)-beta-CD (DM-beta-CD), hydroxypropyl-beta-CD (HP-beta-CD), and carboxymethyl-beta-CD (CM-beta-CD). The stoichiometry ratios of EV and the above five CDs were found to be 1:1. The inclusion ability obeyed the order: CM-beta-CD > HP-beta-CD > TM-beta-CD > DM-beta-CD > beta-CD. The results showed that the modified beta-CDs exhibited stronger binding ability than native beta-CD, especially the charged CM-beta-CD, which implied that the inclusion capacity depends on not only size matching and hydrophobicity but also electrostatic interaction. (HNMR)-H-1 spectra and molecule mechanics calculations suggested that EV was included into the cavity of beta-CD from the wider side.