Abstract

One colorimetric and one fluorescent-indicator displacement assay (IDA) were studied to assess their interaction with methyl viologen (MV), an herbicide commercially known as paraquat. The host-guest complexes formed by cucurbit[7]uril (CB[7]) and the 4-nitroaniline (NA) or Berberine (Be) dyes function as colorimetric- and fluorescent-IDA for MV, respectively. The CB[7]@NA and CB[7]@Be complexes were characterized by UV-vis, fluorescence spectroscopy, and dynamic simulations. Isothermal titration calorimetry (ITC) experiments and dynamic simulations were employed to obtain thermodynamic data for the formation of the 1:1 inclusion complexes. Finally, NA is proposed as a reference colorimetric dye for determining CB[7]-binding affinities using competitive host-guest titrations, and the fluorescent-IDA as the best assay proposed, as it exhibits a high binding constant, a good detection limit of 2.7 x 10-6 mol L-1, good linearity in the range from 4 x 10-6 mol L-1 to 3.5 x 10-5 mol L-1, in aqueous solution. One colorimetric- and one fluorescent-IDA were tested to determine methylviologen. 4-Nitroaniline is tested as the reference colorimetric dye for determining CB[7]-binding affinities. The proposed IDA assays were selectives to MV over the other pesticides.image