The leaves were dried in a hot air oven at 60°C for 24 h. The dried sample was ground into moderate powder. Then, 100 g of the powder was exhaustively extracted with 70% v/v ethanol (EtOH) (1 : 10 w/v) while shaking at 25°C, 120 rpm for 12 h on a shaker. The mixture was filtered through Whatman filter paper no. 1, and the filtrate was concentrated using a rotary evaporator at 40°C. The dark green viscous ethanolic extract (C1) was kept in a tightly closed brown vial at 4°C until used.
A stock solution of the extract was prepared by complete dissolving of 342 mg of the ethanolic extract in 1 mL EtOH using sonication for 30 min. The stock solution was kept at −80°C until used. The working solutions were prepared by diluting the stock solution with EtOH to the concentrations of 3.42, 34.2 and 100 mg/mL.