Inclusion complexes of Schiff bases as phytogrowth inhibitors

This article details the preparation, characterization and phytotoxic evaluation of several Schiff base inclusion complexes obtained from β-cyclodextrin and p-sulfonic acid calix[6]arene. The inclusion complexes (1:1 molar ratio) were prepared by mixing a 5 mmol L^?1 aqueous solution (containing 1 % DMSO) of Schiff bases (guests) with aqueous solution (containing 1 % DMSO) of 5 mmol L^?1 of β-cyclodextrin or p-sulfonic acid calix[6]arene (hosts). The host–guest systems were characterized via a series of NMR experiments. The ability of the complexes to interfere with the radicle elongation of Sorghum bicolor (dicotyledonous species) and Cucumis sativus (monocotyledonous species) was evaluated. After 48 h, the inclusion complexes inhibited the radicle elongation of both species from 11 to 56 %. The formation of inclusion complexes was also investigated theoretically by molecular dynamics simulations in aqueous solution through implicit approach. Based on the experimental observation, the phytotoxic activity evaluated can be attributed to the formation of host–guest systems. This was supported by the theoretical findings based on stable interaction energy analyses for all the studied supramolecular systems.