Characterization and Properties of capsaicin / CD system

The binary systems of capsaicin (CP) andβ-cyclodextrin (βCD) or hydroxypropyl-β-cyclodextrin (HPβCD) were investigated in an attempt to improve formulations of this pesticide. UV spectral shift methods indicated guest-host complex formation between CP and the two cyclodextrins. Phase solubility analysis showed Bs type diagrams with (3CD, AL type with HPPCD indicating the formation of an inclusion complex at 1:1 stoichiometric ratio in solution state. Solubility profiles indicated a 50-fold enhancement of CP solubility could be achieved in the presence of 60 mM HPβCD with respect to CP alone. Solid co-evaporated systems with 1:0.5-1:5 molar ratios of CP/CDs were physicochemically characterized by differential scanning calorimetry (DSC), X-ray diffractometry (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM), revealing that the true inclusion complexes could be formed in the solid CP/βCD systems with 1:5 molar ratio and in the solid CP/HPPCD systems with the molar ratios more than 1:3, respectively. In contrast, crystalline drug was detectable in all other systems. Compared with corresponding physical mixtures, the co-evaporated systems exhibited significant enhancement with regard to CP dissolution. Fruthermore, the stability of CP the co-evaporated systems could increase 10% approximately under the accelerated conditions, compared with pure CP. It was also revealed that complexation of CP with HPβCD had a pronounced improved effect on the pesticide formulations and greatly reduced the amount of CP adsorbed in the soil. For instance,16.7% of CP could be desorped from the soil by complextion while only 3.5% of CP could be desorped without complextion. These results demonstrate that HPβCD may be a preferred excipient, enabling more efficient and intelligent use of CP/CDs inclusion complexes in the development of pesticide formulations.