Hybridization of the natural antibiotic, cinnamic acid, with layered double hydroxides (LDH) as green pesticide.

BACKGROUND, AIM, AND SCOPE: Heavy application of highly toxic synthetic pesticides has been committed to protect crops against insects and diseases, which have brought about serious environmental problems. Thus, an inevitable and fundamental issue has been how to protect crops without harmful effects on nature. As a fascinating nature-compatible approach, we have attempted to hybridize soil-compatible layered double hydroxides (LDHs) with natural antibiotic substances. Only a few of natural antibiotic substances are available for pest control mainly because of their inherent properties such as easy degradability, high minimum inhibition concentration for practical application, and often extremely low availability, whereas LDHs exhibit unique properties such as anion exchange capacity, acid lability, and high affinity to ubiquitous carbonate ion which make them an excellent inorganic matrix to carry labile biomolecules in soils. This study focuses on the behavior of cinnamate-LDH hybrid in soils and the evaluation of its potentials as a green pesticide. MATERIALS AND METHODS: The cinnamate-LDH hybrid was synthesized by a typical coprecipitation method. Cinnamic acid was analyzed by high performance liquid chromatography which was operated at 280 nm with C18 column. Its controlled release property was evaluated in a cultivated soil as well as a simulated soil solution. Its antifungal activity was examined against the growth of Phytophyhora capsici in a potato dextrose agar medium and a red pepper seedling, respectively. RESULTS AND DISCUSSION: Structural characterization by X-ray diffraction, infra-red, and thermal analysis indicates that cinnamate molecules are safely intercalated into the interlayer space of inorganic layers of LDH by the electrostatic interaction to have an empirical formula of Mg(3)Al(OH)(8).CAN . 3.1H(2)O. The overall release pattern of the intercalated cinnamate in the soil solution could be best described by the power-function equation [Formula: see text]. This suggests that diffusion-controlled processes besides simple ion-exchange process play an important role in release of the intercalated cinnamate. Furthermore, its behavior in a cultivated soil clearly shows that hybridization leads to protection of cinnamate against the degradation as well as to a controlled release in soils. Its antifungal activity against the growth of P. capsici in a potato dextrose agar medium and a red pepper seedling definitely shows that the hybrid is very effective in controlling the root rot of red pepper. CONCLUSION: This study demonstrates that the hybridization of natural antibiotic substances with layered double hydroxides could be a fascinating alternative for green formulation of pesticides. This unique hybrid system leads to the salient features such as protection of the substances against chemical and microbial degradations, controlled release, and nature compatibility. RECOMMENDATIONS AND PERSPECTIVES: This study suggests one of the sound strategies to make a breakthrough in the formulation of green pesticides. Hybridization with inorganic matrixes not only enables the natural antibiotic substances to replace the synthetic ingredients but also adjuvants to be excluded from the formulations. Furthermore, the resulting hybrid exhibits a controlled release of the intercalated substances. Although substantiated further, this study is expected to attract a great deal of attention to reliable application of natural antibiotic substances in green protection of crops and agricultural products.

Characteristics of nitrogen release from synthetic zeolite Na-P1 occluding NH4NO3.

Zeolites can accommodate a considerable amount of occluded salt such as NH4NO3, which can serve as a good source of slow-release plant nutrient. This study evaluates the kinetics of ion release from NH4NO3-occluded Na-P1 (N-NaP) using a simulated soil solution and deionized water as leaching solutions. The patterns of ion releases were examined as a function of leaching time under both static and continuous-flow conditions for more than one month. Releases of both NH4+ and NO3- from N-NaP were found to be slow and steady under both the above conditions. The soil solution affected the release of NH4+ and NO3- differently, while deionized water released nearly the same equivalents of these ions. This clearly indicates that ion release from salt-occluded zeolite involves two different reactions, cation exchange and dissolution. The kinetics of ion release from occluded NH4NO3 under static condition was best described by the standard Elovich model while the power function model best expressed these under continuous-flow condition. The initial ion release patterns under both conditions exhibited considerable deviation from the simulated models, probably as a result of the presence of hydrated occluded NH4NO3. Flow condition and the presence of electrolytes in leaching solution affected the release kinetics significantly. Release of occluded NH4NO3 was delayed by the presence of the NH4NO3 coated on zeolite crystals. These results indicate that the ion release property of occluded salt could be predicted and controlled. This study clearly shows that NH4NO3-occluded zeolites could be developed as slow release fertilizers.