Study of antioxidant activity of pyrimidinium betaines by DPPH radical scavenging method

Free radicals cause various human diseases.1 Antioxidants are substances that eliminate free radicals and serve as a defensive factor against their effects in the body. Antioxidants play an important role in the prevention of diseases induced by free radicals2 and systematically reduce their risk by reducing their concentrations.3 They act by inhibiting the initiation and propagation steps, resulting in the end of the reaction and delaying the oxidation process.4 In biological systems, antioxidants have multiple functions, eg it defends against oxidative damage by participating in the main cell signaling pathways and by preventing cell damage caused by the action of reactive oxygen species (ROS). Therefore, antioxidant consumption and the addition of antioxidant in food materials protect the body as well as food from deterioration of oxidation.5 Numerous methods to evaluate the antioxidant activity of specific compounds have been described, but the most widely documented relates to the 2, 2-diphenyl-1-picrylhydrazyl radical (DPPH).6–9 DPPH is stable free radical that accepts an electron or hydrogen to become a stable diamagnetic molecule. In the DPPH radical-scavenging assay, antioxidants react with DPPH, and convert it to yellowcolored diphenylpicrylhydrazine. The color fading extent proves indirectly the radical-scavenging capacity of the antioxidant.6 The reduction of DPPH radical by antioxidants is evaluated by the decrease in absorbance at 517 nm. The decrease in absorbance of DPPH radical caused by antioxidants is due to the reaction between antioxidant molecules and radical progress which results in the scavenging of the radical by hydrogen donation.10 The DPPH tests provided in the literature are based on the same principle as described by BrandWilliams et al.,8 but the analytical protocols differ in several parameters. Evaluation of the methods and modifications for determination of the radical scavenging activity by DPPH shows that the main factors influenced the reproducibility are the solvent, duration of the reaction, sample to reagent ratio and the wave length for absorbance measurement of the decolouration of the reaction mixture.11 Therefore, it is obvious that these factors are of significance for the radical scavenging activity of the tested compounds. Pyrimidinium betaines constitute a class of mesoionic compounds12 which have raised much interest as biologically active compounds.13 Pyrimidinium betaines remain an important class of bioactive heterocyclics due to the presence of the pyrimidine ring in their structure. The literatures indicated that compounds having pyrimidine nucleus have a broad range of biological activities. As a result of their remarkable pharmacological activity, intensive research on pyrimidine derivatives has been focused on their activity, thus constituting an integral part of pharmaceutical industry.14