The binary systems of capsaicin (CP) and b-cyclodextrin (bCD) or hydroxypropyl-b-cyclodextrin (HPbCD) 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 (CDs). Phase solubility analysis showed B s type diagrams with bCD, A L type with HPbCD 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 HPbCD with respect to CP alone. Solid co-evaporated systems (CES) with 1:0.5-1:5 molar ratios of CP/CDs were physicochemically characterized, revealing that the true inclusion complexes could be formed in the solid CP/bCD systems with 1:5 molar ratio and in the solid CP/HPbCD 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 (PMs), the CES exhibited significant enhancement with regard to CP dissolution and the protection from CP degradation under the accelerated conditions. It was also revealed that complexation of CP with HPbCD had a pronounced improved effect on the pesticide formulations and greatly reduced the amount of CP adsorbed in the soil. These results demonstrate that HPbCD may be a preferred excipient, enabling more efficient and intelligent use of CP/ CDs inclusion complexes in the development of pesticide formulations.

No abstract