Ferric chloride

The 2,2′-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,4,6-tripyridyl-s-triazine (TPTZ), potassium persulfate, hydrochloric acid, ferric chloride, iron(II) sulfate heptahydrate, sodium phosphate, sodium hydroxide and ammonium persulfate were purchased from Sigma-Aldrich (Milan, Italy). The phenolic compounds, gallic acid and quercetin, were purchased from Sigma Chemical Co. (St Louis, MO, USA). Analytical grade reagents, such as sodium carbonate, potassium hydroxide, Folin-Ciocalteu reagent, ethanol, methanol and hexane were obtained from Panreac (Barcelona, Spain). Aluminum chloride, potassium ferricyanide, ferric chloride and trichloroacetic acid were from Sigma Chemical Co. (St. Louis, MO, USA). The water was treated in a Milli-Q water purification system (TGI Pure Water Systems, Brea, CA, USA). Coomassie Brilliant blue G250 was purchased from Bio-Rad (Richmond, CA, USA). The spectrophotometer UV-VIS Spectrophotometer 1204 (Shimadzu, Japan) was used. MINOLTA Chromameter CR-300 (Minolta Camera Corp., Meter Division, Ramsey, NJ, USA) equipped with a D65 illuminant, 10° Observer and zero and white calibration was used to measure the color parameters (CIE L*, a*, b*).

To prepare iron oxide nanoparticles, 0.61 g and 1.22 g of ferric chloride (Sigma-Aldrich, Inc., St. Louis, MI, USA) were separately dissolved in distilled water (75 mL) with constant stirring (200 rpm), resulting in 0.05 and 0.1 M ferric chloride solutions. Then, 0.51 and 1.02 mL, containing 50 and 100 mg, respectively, of the concentrated stem bark methanol extract, were separately diluted in 25 mL of distilled water. At room temperature, an aliquot of 50 mg and 100 mg extract solutions (25 mL) was added dropwise to the iron chloride solution (0.05 and 0.1 M, 25 mL) aided by continuous stirring (200 rpm) for 30 min. The production of iron oxide nanoparticles was revealed by a brownish-black colloidal solution (Figure S1). The synthesized nanoparticles were centrifuged (12,000 rpm, 10 min). The residue was dried at 50 °C and kept at 4 °C until use. Accordingly, 50 mg and 100 mg of the extract each were separately reacted with 0.05 M and 0.1 M of the ferric chloride solution, synthesizing four different iron oxide nanoparticles.