ABSTRACT

Objectives:

This study focused on phytochemicals, insecticidal, and bactericidal activities of Cassia nigricans, as well as the molecular docking analysis for acetylcholinesterase inhibitor (AChEI) as a promising natural insecticide.

Material and 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. Compound 1 was analyzed for physicochemical and pharmacokinetic parameters and molecular docking against an AChE protein (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. Emodin could be a promising candidate for insecticidal pest control.