Inclusion complexation of carbaryl and β-cyclodextrin in solution and in the solid state

This study was carried out with the aim of investigating the interactions between β-cyclodextrin and carbaryl, a carbamate pesticide, and their effect on some physico-chemical properties of carbaryl, such as aqueous solubility and lipophilicity. The interactions between carbaryl and β-cyclodextrin were thoroughly investigated both in solution and in the solid state. The effect of β-cyclodextrin on the aqueous solubility of carbaryl was evaluated by the phase solubility method. The amount of carbaryl dissolved increased linearly with the addition of β-cyclodextrin according to an AL type plot and without precipitation of the complex. The apparent stability constant of the complex was 289 ± 21 M-1, assuming a 1:1 stoichiometry; this value was confirmed by a method based on circular dichroism measurements. Equimolar carbaryl/β-cyclodextrin solid systems were prepared by physical-mixing and freeze-drying, and fully characterised by Differential Scanning Calorimetry, X-ray powder diffractometry and Fourier Transform Infra-Red analysis. The results of the solid state study demonstrated that the freeze-drying method yields a system with a high degree of amorphisation and yields an inclusion complex. The dissolution profile of the pesticide was affected by the physico-chemical properties of each solid system, the freeze-dried form dissolving more rapidly. However, the physical association of β-cyclodextrin and carbaryl enhanced the aqueous solubility of the insecticide as well.