Phytochemicals, antioxidant studies of deinbollia pinnata (Poir.) schumach. & thonn. and its uses in the synthesis of titania nanoparticles

Abstract

Sapindaceae is a tropical and sub-tropical continental plant. Phytochemical studies on D. pinnata, its antioxidant activity and application in the photodegradation of methyl orange dye were conducted. The sonication/agito-sonication method was used for leaves and root bark samples. Optimal sonication conditions were obtained at a temperature of 45°C, a time of 35 mins and a solvent ratio MeOH:H2O (1:1) for a yield of 83.01%. Fractionation and purification on the extracts of the aerial parts and root bark using chromatographic methods produced eighteen compounds. The compounds were identified spectroscopically and compared with literature data. These compounds include pyrogallol, methyl gallate, ethyl gallate, methyl-ß-D-glucopyranoside, squalene, γ-sitosterol, lupeol, stigmasterol, taraxasterol and stigmasta-5,22-diene-3-ol acetate, ethyl oleate, ethyl stearate, stearic acid, palmitic acid, myristic acid, phytyl palmitate, and 4,8,12,16-tetramethylheptadecan-4-olide. Alkaloids, sugars, phenolics, tannins and steroids were present in all the plant parts. Saponins, terpenes and flavonoids were found in leaves and root bark, while root bark and heartwood possessed quinones. The methanol extracts demonstrated total phenolic content at 75.93 ± 2.05 GAE (mg GAE/g dw) and total flavonoid content at 88.41 ± 0.56 QUE (mg QUE/g dw). The extracts showed good DPPH (2,2-diphenyl-1-picrylhydrazyl) scavenging activity with a percentage inhibition of more than 70% at 125 ppm. The methanol extracts showed excellent antioxidant activity towards (ABTS) (2,2’-azino-bis-3-ethylbenzthiazoline-6-sulphonic acid) assay with SC50 value of 13.68 µg/mL. The methanolic extracts also exhibited an equivalent FRAP (Ferric reducing antioxidant power) value of 3.45 ± 1.30 mM. Methyl gallate displayed the highest antioxidant radical scavenging activity towards DPPH assay with an SC50 value of 0.19 µg/mL and pyrogallol showed the highest ABTS activity with an SC50 value of 7.44 µg/mL. Ethyl gallate showed good potential as a ferric ion reducer from 0.69 ± 0.00 to 3.22 ± 0.03 mM FRAP, respectively. The TiO2 NPs was prepared using D. pinnata leaves extracts of different polarities. X-ray diffraction (XRD) pattern confirmed the synthesized TiO2 consisted of anatase phase in high purity, with average crystallite size in the range of 19 - 21 nm. Characterization using field emission scanning electron microscopy (FESEM) showed uniform semi-spherical shape in the size range of 33 - 48 nm. The energy dispersive X-ray (EDX) spectrum shows two peaks for the main elements of Ti (61 wt.%) and O (35 wt.%). The 3.2 eV band-gap energy was determined using UV-Vis spectroscopy. Nitrogen sorption analysis showed that the type V isotherm was obtained, with a Brunauer-Emmett-Teller (BET) surface area of 31.77 m2/g. The photocatalytic activity of TiO2 NPs was evaluated for methyl orange (MO) photodegradation under UV light irradiation. TiO2 NPs synthesized with ethyl acetate extract of D. pinnata leaves showed the most effective photodegradation performance, achieving 98.7% of MO conversion within 150 mins. The application of plant extracts using TiO2 successfully produced crystalline TiO2 anatase with superior photocatalytic activity in the process of photodegradation of organic dyes.