Ahmed S., Shakeel F. (2012). Antioxidant activity coefficient, mechanism, and kinetics of different derivatives of flavones and flavanones towards superoxide radical. Czech J. Food Sci., 30: 153-163.A systematic investigation of the electrochemically generated superoxide radical (O 2•-) has been conducted in the presence of some flavonoids. Cyclic voltammetry was used to generate O 2 •-by reducing the molecular oxygen in DMSO at room temperature. The scavenging of the radical was monitored by the decrease in anodic or/and cathodic currents while linearly increasing the concentration of the flavonoid. The strength of interaction was quantified in terms of the binding constant (K b ) values ranging from 1 × 10 2 and 5 × 10 3 M -1 . The antioxidant activity coefficient (K ao ) was calculated from the linear part of the plot of 'current decrease vs. flavonoid concentration' . Radical scavenging mechanism of the antioxidant was proposed and discussed in terms of the structure activity relationship. Nicholson-Shain method was employed to estimate the bimolecular homogeneous kinetics and on this basis control use of antioxidant is pointed out.
A cyclic voltammetric method is presented for the determination of antioxidant activity of flavonoids in the presence of DPPH • as target radical. The method depends on the scavenging effect of the radical as monitored by the decrease in peak currents accompanying an increase in the concentration of flavonoids. For this purpose the electrochemical behavior of DPPH was investigated in DMSO at 25 ± 0.5 • C. The antioxidant activity coefficient, (K ao ), was estimated from the linear part of a plot of the change in current density vs flavonoid concentration. The antioxidant capacity index (IC 50 , corresponding to 50% consumption of DPPH • ) was also calculated from the proportional current decrease for a relative comparison among the flavonoids. Mechanism of the electrochemical process is explicated and it is proposed that hydrogen atom transfer (HAT) from the flavonoid to DPPH • is responsible for the antiradical activity. The proposed electrochemical analysis is validated by the well established UV-Visible spectroscopic method.
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