betadex and dichlorfop-methyl

Cyclodextrins (CDs) possess a hydrophilic external surface and a hydrophobic cavity. They are thus highly soluble and, in the meantime, effectively form inclusion complexes with hydrophobic organic compounds to enhance their solubilities. In this study, the complexation between modified beta-CDs and the herbicide diclofop-methyl (DM), (2-(4-(2,4-dichlorophenoxy)-phenoxy) propionate), was investigated. The complexation was confirmed by the shifts in the wavelengths of maximum ultra violet (UV) absorption and fluorescence excitation/emission. The deuterium isotope effects indicate that in the presence of beta-CDs the solubility of DM was lower while that of diclofop was higher in D2O than in H2O, suggesting the primary role of hydrophobic interactions in complexation. The solubility of DM was enhanced in the presence of beta-CDs, the extent of which depended on the modification of beta-CDs. The complexation reduced the hydrolysis of DM and hence increased its stability. The small inconsistency in the power of beta-CDs between hydrolysis retardation and solubilization suggests that hydrolysis was affected by the properties of beta-CDs and the configuration of DM in the complexes. Use of beta-CDs may thus result in the mobilization of soil DM. Properly modified beta-CDs may be utilized as formulation additives for improved delivery of DM and for enhanced environmental remediation.

Topics: Adsorption; beta-Cyclodextrins; Chromatography, High Pressure Liquid; Environment; Halogenated Diphenyl Ethers; Herbicides; Hydrolysis; Phenyl Ethers; Soil; Solubility; Spectrometry, Fluorescence; Ultraviolet Rays

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.

Topics: Adsorption; beta-Cyclodextrins; Environment; Halogenated Diphenyl Ethers; Herbicides; Methylation; Phenyl Ethers; Soil; Solubility; Spectrometry, Fluorescence; Spectrophotometry, Ultraviolet; Spectroscopy, Fourier Transform Infrared