One-Step Encapsulation of ortho-Disulfides in Functionalized Zinc MOF. Enabling Metal-Organic Frameworks in Agriculture

Abstract

Application of natural products as new green agrochemicals with low average lifetime, low concentration doses, and safety is both complex and expensive due to chemical modification required to obtain desirable physicochemical properties. Transport, aqueous solubility, and bioavailability are some of the properties that have been improved using functionalized metal-organic frameworks based on zinc for the encapsulation of bioherbicides (ortho-disulfides). An in situ method has been applied to achieve encapsulation, which, in turn, led to an improvement in water solubility by more than 8 times after 2-hydroxypropyl-β-cyclodextrin HP-β-CD surface functionalization. High-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) and integrated differential phase contrast (iDPC) imaging techniques were employed to verify the success of the encapsulation procedure and crystallinity of the sample. Inhibition studies on principal weeds that infect rice, corn, and potato crops gave results that exceed those obtained with the commercial herbicide Logran. This finding, along with a short synthesis period, i.e., 2 h at 25 °C, make the product an example of a new generation of natural-product-based herbicides with direct applications in agriculture.

Keywords: MOF; encapsulation; herbicide; iDPC; weed control.

Figure 1

Ortho-disubstituted disulfides selected for encapsulation in zinc imidazolate frameworks and their molecular volumes.

Figure 2

Low (A) and medium (B) magnification HAADF images of the MOF@DiS–NH₂ sample. (C) MOF particle size distribution histogram.

Figure 3

STEM-XEDS chemical maps and HAADF image of MOF@DiS–NH₂. The Zn and S intensity profiles extracted from the red arrow marked on the Zn–S map (Zn is shown in blue and S in black).

Figure 4

High-resolution high-angle annular dark-field scanning transmission electron microscopy (HR HAADF-STEM) and integrated differential phase contrast (iDPC) images of MOF@DiS–NH₂. Enlargement and the digital diffraction pattern (DDP) of the whole image are shown as insets in the iDPC image.

Figure 5

Results of a coleoptile bioassay at pH 7.0 during 24 h.

Figure 6

(Top) ¹H NMR kinetic study to analyze the integral value with time. (Bottom) Changes in the integrals with time.

Figure 7

(Top) SEM images of the samples modified using different concentrations of the surface functionalizing agent. (Bottom) ζ-potential values for each concentration.

Figure 8

Low (A) and medium (B) magnification HAADF images of MOF@DiS–NH₂ functionalized with 0.6 mg/mL HP-β-CD. (C) Crystallite size histogram of the functionalizedMOF@DiS–NH₂ sample.

Figure 9

STEM-XEDS chemical maps and HAADF image of the functionalizedMOF@DiS–NH₂ sample. Zn and S intensity profiles along the red arrow marked on the combined Zn–S map are also displayed.

Figure 10

Integrated differential phase contrast (iDPC) image recorded on the functionalizedMOF@DiS–NH₂ sample. The DDP of the whole image is shown as an inset.

Figure 11

HPLC release study of DiS–NH₂ from 0.6 mg/mL HP-β-CD functionalizedMOF@DiS–NH₂.

Figure 12

Coleoptile bioassay at pH 5.6 during 48 h.

Figure 13

Results of the phytotoxicity bioassay against E. crus-galli, A. viridis, and L. rigidum. Positive values indicate stimulation of growth vs the control and negative values indicate inhibition. Significance levels p < 0.01 (a) or 0.01 < p < 0.05 (b).