The study aimed to prepare inclusion complexes of 1,3-diphenylurea
(DPU) with β-cyclodextrin (βCD) and 2-hydroxypropyl-β-cyclodextrin
(HP-βCD) 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
(
K
s
) and complexation efficiency (CE)
of βCD/DPU were found to be
K
1/1
= 250 M
–1
, CE = 2.48× 10
–3
. The
K
s
and CEs of HP-βCD/DPU
were found to be
K
1/1
= 427 M
–1
, CE = 3.93 × 10
–3
and
K
2/1
= 196 M
–1
, CE = 1.93 × 10
–3
respectively. The powder X-ray diffraction results of 3DGM (βCD/DPU
= 2/1, HP-βCD/DPU = 2/1) showed that the diffraction peaks originating
from the DPU and βCD disappeared, indicating a halo pattern.
Differential scanning calorimetry results showed an endothermic peak
at 244 °C derived from the melting point of DPU, but the endothermic
peak disappeared in the 3DGM (βCD/DPU = 2/1, HP-βCD/DPU
= 2/1). Near-infrared absorption spectra showed peak shifts in 3DGM
(βCD/DPU and HP-βCD/DPU) at the −CH and −NH
groups of DPU and the −OH groups of βCDs and free water.
In the dissolution test (after 5 min), the concentration of intact
DPU was 0.083 μg/mL. However, the dissolution concentrations
of DPU in the 3DGM (βCD/DPU = 1/1), 3DGM (βCD/DPU = 2/1),
3DGM (HP-βCD/DPU = 1/1), and 3DGM (HP-βCD/DPU = 2/1) were
3.27, 3.64, 5.70, and 7.03 μg/mL, respectively, indicating higher
solubility than that of the intact DPU. Further,
1
H–
1
H NOESY NMR spectroscopic measurements showed cross-peaks
between H-A (7.32 ppm) and H-B (7.12 ppm) of DPU and H-6 (3.79 ppm)
in the βCD cavity of the 3DGM (βCD/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 βCD cavity. The results of the broccoli sprout
cultivation experiment showed that 3DGM (βCD/DPU = 1/1), 3DGM
(βCD/DPU = 2/1), 3DGM (HP-βCD/DPU = 1/1), and 3DGM (HP-βCD/DPU
= 2/1) increased the stem thickness compared with that of the control
group (DPU). These results indicated that the βCD/DPU and HP-βCD/DPU
inclusion complexes were formed by the three-dimensional mixing and
milling method, which enhanced the solubility and plant growth-promoting
effects.