Characterization, Preparation, and Promotion of Plant Growth of 1,3-Diphenylurea/-Cyclodextrin Derivatives Inclusion Complexes

The study aimed to prepare inclusion complexes of 1,3-diphenylurea (DPU) with ss-cyclodextrin (ss CD) and 2hydroxypropyl-ss-cyclodextrin (HP-ss CD) using a three-dimensional ground mixture (3DGM). Their physicochemical properties, intermolecular interactions, solubilities, and plant growth-promoting activities were investigated on broccoli sprouts. Phase-solubility diagrams indicated the stability constant (Ks) and complexation efficiency (CE) of ss CD/DPU were found to be K1/ 1 = 250 M-1, CE = 2.48x 10-3. The Ks and CEs of HP-ss CD/DPU were found to be K1/ 1 = 427 M-1, CE = 3.93 x 10-3 and K2/ 1 = 196 M-1, CE = 1.93 x 10-3 respectively. The powder X-ray diffraction results of 3DGM (ss CD/DPU = 2/1, HP-ss CD/DPU = 2/1) showed that the diffraction peaks originating from the DPU and ss CD disappeared, indicating a halo pattern. Differential scanning calorimetry results showed an endothermic peak at 244 degrees C derived from the melting point of DPU, but the endothermic peak disappeared in the 3DGM (ss CD/DPU = 2/1, HP-ss CD/DPU = 2/1). Near-infrared absorption spectra showed peak shifts in 3DGM (ss CD/DPU and HP-ss CD/DPU) at the -CH and -NH groups of DPU and the -OH groups of ss CDs and free water. In the dissolution test (after 5 min), the concentration of intact DPU was 0.083 mu g/mL. However, the dissolution concentrations of DPU in the 3DGM (ss CD/DPU = 1/1), 3DGM (ss CD/DPU = 2/1), 3DGM (HP-ss CD/DPU = 1/1), and 3DGM (HP-ss CD/DPU = 2/1) were 3.27, 3.64, 5.70, and 7.03 mu g/mL, respectively, indicating higher solubility than that of the intact DPU. Further, 1H-1H NOESY NMR spectroscopic measurements showed cross-peaks between HA (7.32 ppm) and H-B (7.12 ppm) of DPU and H-6 (3.79 ppm) in the ss CD cavity of the 3DGM (ss CD/DPU = 2/1). A cross-peak was also observed among DPU H-A (7.32 ppm), H-B (7.11 ppm), and H-6 (3.78 ppm) in the ss CD cavity. The results of the broccoli sprout cultivation experiment showed that 3DGM (ss CD/DPU = 1/1), 3DGM (ss CD/DPU = 2/1), 3DGM (HP-ss CD/ DPU = 1/1), and 3DGM (HP-ss CD/DPU = 2/1) increased the stem thickness compared with that of the control group (DPU). These results indicated that the ss CD/DPU and HP-ss CD/DPU inclusion complexes were formed by the three-dimensional mixing and milling method, which enhanced the solubility and plant growth-promoting effects.