Interaction of gold nanoparticles with free radicals and their role in enhancing the scavenging activity of ascorbic acid.
The present study investigates the interaction of citrate stabilized gold nanoparticles (12±1.5nm) (GNPs) with free radicals; 1,1-diphenyl-2-picrylhydrazyl (DPPH) stable and electrochemically generated superoxide, O2(-). Different experiments were designed to understand the interaction between GNPs and DPPH by employing cyclic voltammetry, UV-vis spectroscopy and computational chemistry using 6-311G basis set. The increase in heterogeneous rate constant, ksh, of DPPH upon addition of GNPs pointed towards possible complex formation, DPPH-GNPs which were further explained by a model assuming surface adsorption of DPPH on GNPs. Further, the model was validated by studying interaction of GNPs with a biologically important free radical, O2(-). Exciting result in terms of disappearance of anodic peak after GNPs addition confirmed that gold nanoparticles interacted with stable as well as unstable free radicals. Also, the stoichiometry of the most stable complex GNP-DPPH was determined from UV-vis spectroscopy by applying Job's method. The GNP-DPPH complex was found to be active with 46.0% reduction of the IC50 value of standard antioxidant, ascorbic acid (AA), indicating its role in enhancing antioxidant activity. Hence, this study presents a simple and potential approach to enhance the efficiency of natural antioxidants without modifying their structure, or involving the complex functionalization of GNPs with antioxidants.
Nanoscience and Catalysis Division, National Centre for Physics, Islamabad 44000, Pakistan.
Humaira
H
Razzaq
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan.
Farhat
F
Saira
Chemistry Division, Directorate of Science, Pakistan Institute of Nuclear Science and Technology (PINSTECH), P.O. Nilore, Islamabad 45650, Pakistan.
Azra
A
Yaqub
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan. Electronic address: r_qureshy@yahoo.com.
Rumana
R
Qureshi
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan.
Misbah
M
Mumtaz
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan.
Samia
S
Saleemi
D000975:Antioxidants / Q000737:chemistry; D001205:Ascorbic Acid / Q000737:chemistry*; D055664:Electrochemical Techniques; D005609:Free Radicals / Q000737:chemistry*; D006046:Gold / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*
D000975:Antioxidants; D005609:Free Radicals; D006046:Gold; D001205:Ascorbic Acid
Cyclic voltammetry; Free radical; Gold nanoparticles; Heterogeneous kinetics; Surface adsorption