Insecticidal and Bactericidal activities of Cassia Nigricans and Molecular Docking analysis on Insect Acetylcholinesterase

INTRODUCTION: This study focused on phytochemicals, insecticidal and bactericidal activities of Cassia nigricans, as well as the molecular docking analysis for acetylcholinesterase inhibitor (AChEI) as promising natural insecticides.
METHODS: The leaves of C. nigricans were extracted successively with n-hexane, acetone, and methanol. Silica gel column chromatography of the methanol extract yielded compound 1. The insecticidal properties of the extracts and compound 1 were evaluated by contact toxicity against Sitophilus zeamais.The bactericidal activity was achieved by photodynamic inactivation of faecal coliforms and faecal enterococci in water using extracts and compound 1 as natural photosensitizers. Molecular docking and ADMET properties were performed for compound 1 against one protein of insect AChE (6XYU).
RESULTS: Compound 1 was characterized as emodin (1,3,8-trihydroxy-6-methylanthracene-9,10-dione) using 1D-2D-1H-13C NMR and MS methods. The insecticidal properties showed that emodin exhibited the highest toxicity with an LC50 = 5.00 mg/mL compared to all extracts. The n-hexane extract showed the highest insecticidal activity (LC50 = 177.48 mg/mL) compared to the methanol (LC50 = 195.08 mg/mL) and acetone (LC50 = 374.14 mg/mL) extracts. Complete inhibition of faecal enterococci by photosensitization was observed after 60 minutes of light exposure of emodin treated water at all concentrations used (1-5 mg/mL) and 120 minutes for faecal coliforms under the same conditions.Based on the docking score, the binding energy of emodin (-6.38 kcal/mol) is close to that of the marketed insecticide pirimiphos-methyl (-6.25 kcal/mol). In addition, emodin was subjected to insecticide probability prediction and absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis and was found to be satisfactory as a natural insecticide.
DISCUSSION AND CONCLUSION: This study reported the isolation of emodin from C. nigricans for the first time. The leaves of C. nigricans could be used as a natural insecticide and bactericidal agent. Emodin could be a promising candidate for insecticidal pest control.