Kinetics of the Antioxidant Activities of Solanum macrocapon and Crassocephalum rubens by DPPH Radical Scavenging Method



Kinetics of the antioxidant activities of two edible vegetables; Solanum macrocapon (S.macrocapon) and Crassocephalum rubens (C.rubens) was investigated. The methanolic extracts of the samples were tested with 2,2-diphenyl-1-picrylhydrazyl (DPPH) at different times (30, 50, 70 and 90 minutes). UV-Visible Spectroscopy technique was employed  to evaluate the ability of the plant extracts to scavenge DPPH radicals by measuring the absorbance at the various experimental times. The concentration of sample required to inhibit 50

% of the DPPH free radical (IC50) and kinetic parameter (rate constant k2) were determined from the absorbances values. S.macrocapon and C.rubens had DPPH scavenging potency with IC50 values of 2.18 x 10-2 mgml-1 and 6.27 x 10-2 mgml-1 respectively. This implied that S.macrocapon is a more potent antioxidant than C.rubens. The rate constant for the hydrogen atom abstraction by DPPH (k2) in the presence of S.macrocapon is 2.70 x 10-3 ± 0.0006 mlmg- 1min-1 with R2 value of 0.709 while for C.rubens, the rate constant is 6.89 x 10-4  ± 0.03 x 10-4 mlmg-1min-1 with R2 value of 0.987 using Pseudo-first order kinetics model. However, under second order kinetics, the rate constant, k2, for S.macrocapon is 4.73 x 10-1 ± 0.020 mM-1min-1 with R2 value of 0.993 while C.rubens has k2 value of 5.55 x 10-2 ± 0.00236 mM-1min-1 with R2 value of 0.795. Thus, the depletion of DPPH by S.macrocapon followed a second order kinetics while that of C.rubens followed a Pseudo first order kinetics.


Keywords: Kinetics, DPPH, Antioxidant, UV-Vis spectroscopy, IC50


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