Gnidia glauca Leaf and Stem Extract Mediated Synthesis of Gold Nanocatalysts with Free Radical Scavenging Potential

Abstract

Development of eco-friendly and novel method for the synthesis of metal nanoparticles is one of the most popular and emerging aspect of nanobiotechnology. In this report, Gnidia glauca leaf and stem extract are used to synthesize gold nanoparticles (AuNPs). As compared to other biological methods, the syntheses were extremely rapid leading to complete reduction within 20 min. Transmission and high resolution transmission electron micrographs clearly indicated that majority of the bioreduced nanoparticles were spherical within a size range of 10 to 60 nm. Exotic shapes like gold nanotriangles and nanohexagons were found in a range between 100 to 300 nm. Dynamic light scattering validated the size range that was observed in TEM and HRTEM. Unique pattern confirming the self-assembly of spheres into anisotropic nanoparticles of larger dimensions was exhibited in HRTEM images. X-ray diffraction pattern and energy dispersive spectroscopic analysis confirmed the purity of elemental gold in the bioreduced nanoparticles. Fourier infrared spectral analysis indicated the role of the phenolic groups in reduction of chloroauric acid into AuNPs. Efficient reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in the presence of AuNPs and NaBH4 with apparent rate constants (k) 1.99 × 10-3 min-1 and 4.498 × 10-3 min-1, for AuNPs reduced by GGLE and GGSE, respectively provided strong evidence for the catalytic potential. AuNPs synthesized by GGSE and GGLE showed a second order rate constant of 1.78 × 107 and 1.31 × 107 respectively confirming the scavenging of ABTS•+ radicals.