Fabrication of supramolecular self-assembly of the Schiff base complex for improving bioavailability of aldehyde-containing plant essential oil

Plant essential oils have enormous potential in the management of crop disease for their easy availability, biocompatibility, biodegradability, and excellent antimicrobial activities. However, these substances usually show poor performance in practical applications due to the poor stability caused by their volatilization and oxidation. Herein, taking advantage of the biological characteristics that some plant pathogenic microorganisms can acidify microenvironment, a pH-responsive supramolecular self-assembly based on the Schiff base complex of cinnamaldehyde (Cin) and branched polyethylenimine (BPEI) was constructed through multiple covalent and noncovalent interactions. The results showed that the formation and physicochemical properties of the self-assembly were positively correlated with the molecular weight of BPEI. Combined with the stability, particle size, zeta potential, self-assembly rates, and morphological characteristics in different systems, BPEI with an average molecular weight of 10,000 (BPEI 10 k) was a preferable choice to push the formation of the self-assembly and the optimum mass ratio of Cin to BPEI 10 k was 3:4. The prepared spherical nanoparticles had low volatility, good surface activity, and high stability and could respond to acidic environments to release Cin by a Fickian diffusion or a non-Fickian behavior. The self-assembly exhibited superior activities against plant pathogenic fungi, desirable environmental compatibility, and convincing biosafety to the plants. These findings would provide guidance for achieving efficient utilization of aldehyde-containing plant essential oil and exploring a useful approach for sustainable plant disease management.