Razzaq Humaira, Saira Farhat, Yaqub Azra, Qureshi Rumana, Mumtaz Misbah, Saleemi Samia
Nanoscience and Catalysis Division, National Centre for Physics, Islamabad 44000, Pakistan.
Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan.
J Photochem Photobiol B. 2016 Aug;161:266-72. doi: 10.1016/j.jphotobiol.2016.04.003. Epub 2016 Apr 9.
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.
本研究调查了柠檬酸盐稳定的金纳米颗粒（12±1.5纳米）（GNPs）与自由基的相互作用；1,1-二苯基-2-苦基肼（DPPH）稳定自由基以及电化学产生的超氧阴离子O2(-)。设计了不同的实验，通过循环伏安法、紫外-可见光谱法以及使用6-311G基组的计算化学方法来理解GNPs与DPPH之间的相互作用。加入GNPs后DPPH的异相速率常数ksh增加，表明可能形成了复合物DPPH-GNPs，这通过一个假设DPPH在GNPs表面吸附的模型得到了进一步解释。此外，通过研究GNPs与一种具有生物学重要性的自由基O2(-)的相互作用对该模型进行了验证。加入GNPs后阳极峰消失这一令人兴奋的结果证实了金纳米颗粒与稳定和不稳定的自由基都发生了相互作用。同时，通过应用乔布法从紫外-可见光谱法确定了最稳定的复合物GNP-DPPH的化学计量比。发现GNP-DPPH复合物具有活性，标准抗氧化剂抗坏血酸（AA）的IC50值降低了46.0%，表明其在增强抗氧化活性方面的作用。因此，本研究提出了一种简单且有潜力的方法，无需改变天然抗氧化剂的结构，或使GNPs与抗氧化剂进行复杂的功能化，就能提高其效率。
