Environmental effects of inclusion complexation between methylated β-cyclodextrin and diclofop-methyl

Diclofop-methyl (DM) is a broad-spectrum herbicide but often shows a reduced biological activity against the target grasses due to its poor water solubility and slow translocation within plant tissues. Randomly methylated beta-cyclodextrin (MCD) is an effective inclusion complexation agent and, as a potential formulation additive, may thus improve the behavior of DM. We evaluated the complexing role of MCD by measuring the solubility and soil sorption of DM as a function of MCD concentration, as well as the dissolution rates of DM-MCD complexes. The complex was also extensively characterized by UV, fluorescence, Fourier transform infrared, nuclear magnetic resonance, and differential scanning calorimetry techniques. The apparent solubility of DM linearly increased with MCD concentration, indicating the formation of a 1:1 complex. In contrast, diclofop was not complexed by MCD. The DM-MCD complex appeared to have formed within the hydrophobic cavity of MCD. With the measured stability constant of 4740 L mol(-1), the complex was apparently stable, which resulted in DM resistant to hydrolysis, and hence the ratio of DM to the sum of DM and diclofop increased toward unity with increasing MCD concentration. The DM-MCD complex also quickly dissolved to a maximum within 5 min, due presumably to the hydrophilicity of MCD. The sorption of DM by soil was significantly reduced in the presence of MCD. All the results suggest that MCD may effectively improve the availability of DM to pests and for bioremediation.