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

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.


Synthesis of MOF@ DiS-NH2 and MOF@DiS-O-Acetyl.
The method is a modification of that reported by Liédana [13] . DiS-NH2 (0.4 mmoles) was dissolved in MeOH (30 mL) together with Zn(NO3)2 (1 mmol). This mixture was added dropwise to a solution of 2methylimidazole (10 mM) in MeOH. The mixture was stirred at room temperature for 2 h.
The resulting solution was centrifuged at 15000 rpm for 15 min and the supernatant was removed. The solid precipitate was washed three times with distilled water and dried in a vacuum oven (35 ºC) overnight. Samples were stored at -20 ºC under a nitrogen atmosphere.
Electron microscopy studies. Samples for scanning electron microscopy were prepared by depositing a tiny portion of the solid directly onto a 3 mm, lacey-carbon coated 200 mesh copper grid.
The large area views of the samples were recorded using the scanning transmission electron microscopy (STEM) detector installed on an FEI Nova NanoSEM 450 scanning electron microscope. Bright-field (BF), dark-field (DF), and high-angle annular dark-field (HAADF) images were recorded using the annular-type detector installed on this microscope.
Ultra-high resolution scanning transmission electron microscopy (STEM) studies were performed on a double Aberration-Corrected (AC) FEI Titan Cubed Themis 60-300 microscope operated at 300 kV. The equipment was also equipped with a Super X-G2 X-ray high sensitivity energy-dispersive spectrometer, thus providing a tool to simultaneously combine spectroscopy and image signals. and DiS-O-Acetyl were 0.9985 and 0.9988, respectively. The gradient method is shown in Table S1 for DiS-NH2 and Table S2 for DiS-O-Acetyl. The retention time, area, mean area and standard deviation for each compound are shown in Table S3 and Table S4.

Water solubility measurements. To analyze the solubility enhancement, MOF@ DiS-NH2
and MOF@DiS-O-Acetyl were dispersed in distilled water and shaken with a vortex. After 24 h, the samples were analyzed by HPLC applying the quantification method described previously in order to ascertain the levels of disulfides that could be solubilized. The percentages shown in Tables 1 and 2 (Results and discussion) are the results obtained after applying Equation 1. All of the information related to the the HPLC analysis for the water solubility of the free compounds is provided in Table S5.

Solubility enhancement (%) = Water solubility when encapsulated
Water solubility of free compound · 100 (Eq. 1) Encapsulation efficiency. The encapsulation percentage was evaluated by the standard method reported in literature [4] . Organic solvents and ultrasound were applied to break the MOF structure and release all the encapsulated compound. The calculations were carried out using Equation 2. The information on the encapsulation percentage is provided in Table S6. Germination and growth were conducted in aqueous solutions at controlled pH by using 10 −2 M 2-[N-morpholino]ethanesulfonic acid (MES) and 1 M NaOH (pH 6.0). The compounds to be assayed were dissolved in water only and these solutions were diluted with buffer so that test concentrations for each compound (10 −3.3 × 10 −4 , 10 −4.3 × 10 −5 and 10 −5 M) were achieved. Four replicates were used for each weed species, each containing 20 seeds.
Treatment, control or internal reference solution (1 mL) was added to each Petri dish. After adding the seeds and aqueous solutions, Petri dishes were sealed with Parafilm ® to ensure closed-system models. Seeds were further incubated at 25 °C in a Memmert ICE 700 S-7 controlled environment growth chamber. The photoperiod was 16/8 h light/dark for barnyardgrass, annual ryegrass and redroot pigweed. Bioassays took 8 days. After growth, plants were frozen at −10 °C for 24 h to avoid subsequent growth during the measurement process. Evaluated parameters (germination rate, root length, and shoot length) were recorded using a Fitomed system [25] , which allowed automatic data acquisition and statistical analysis using its associated software. Data were analyzed statistically using Welch's test, with significance fixed at 0.01 and 0.05. Results are presented as percentage differences from the control. Zero represents control, positive values represent stimulation, and negative values represent inhibition.
S-8 Figure S1. XRD comparison between empty MOF and MOF@DiS-NH2 at the same temperature.