Spectrophotometric and thermoanalytical study of cypermethrin/cyclodextrin complexes

Cypermethrin/beta-CD complexes were prepared at 1:2 cypermethrin/beta-CD molar ratio by different complexation methods: conventional coprecipitation, suspension and kneading methods as well as "melting in solution" technique, which was developed in our laboratory. The complexes were investigated by UV-spectrophotometry and thermal analysis. It was found that complexes made by coprecipitation, suspension and kneading methods contained cypermethrin not only in complexed but also in uncomplexed form. The guest molecule in the complex prepared by "melting in solution" technique showed to be completely complexed, so it was the most effective complexation method studied. Investigating the solubility of cypermethrin with different cyclodextrins (CDs), it was established that the increase of solubility of cypermethrin was the highest in case of methylated cyclodextrins. The equilibrium constants were calculated from solubility isotherms. On the basis of these results, the heptakis(2,6-di-O-methyl)-beta-cyclodextrin (DIMEB) complex was the more stable. By UV-irradiation measurements it was found that the photodegradation of cypermethrin was inhibited by methylated beta-CDs. (C) 2004 Elsevier B.V. All rights reserved.