Gnidia glauca and Dioscorea bulbifera are traditional medicinal plants that can be considered as sources of natural antioxidants. Herein we report the phytochemical analysis and free radical scavenging activity of their sequential extracts. Phenolic and flavonoid content were determined. Scavenging activity was checked against pulse radiolysis generated ABTS•+ and OH radical, in addition to DPPH, superoxide and hydroxyl radicals by biochemical methods followed by principal component analysis. G. glauca leaf extracts were rich in phenolic and flavonoid content. Ethyl acetate extract of D. bulbifera bulbs and methanol extract of G. glauca stem exhibited excellent scavenging of pulse radiolysis generated ABTS•+ radical with a second order rate constant of 2.33×106 and 1.72×106, respectively. Similarly, methanol extract of G. glauca flower and ethyl acetate extract of D. bulbifera bulb with second order rate constants of 4.48×106 and 4.46×106 were found to be potent scavengers of pulse radiolysis generated OH radical. G. glauca leaf and stem showed excellent reducing activity and free radical scavenging activity. HPTLC fingerprinting, carried out in mobile phase, chloroform: toluene: ethanol (4: 4: 1, v/v) showed presence of florescent compound at 366 nm as well as UV active compound at 254 nm. GC-TOF-MS analysis revealed the predominance of diphenyl sulfone as major compound in G. glauca. Significant levels of n-hexadecanoic acid and octadecanoic acid were also present. Diosgenin (C27H42O3) and diosgenin (3á,25R) acetate were present as major phytoconstituents in the extracts of D. bulbifera. G. glauca and D. bulbifera contain significant amounts of phytochemicals with antioxidative properties that can be exploited as a potential source for herbal remedy for oxidative stress induced diseases. These results rationalize further investigation in the potential discovery of new natural bioactive principles from these two important medicinal plants.

The reaction of hydroxyl radical ((•)OH) with guanine was investigated under restricted pH condition (pH 4.6) using pulse radiolysis technique. The time-resolved optical transient absorption spectra showed two peaks centered at 300 and 330 nm at 4 μs after the pulse which exhibited different reactivity toward molecular oxygen (O(2)). The peak at 300 nm was found to be relatively more stable than the peak at 330 nm. The peak corresponding to 330 nm decayed within 20 μs having a first order rate constant 4-7 × 10(4) s(-1) and was pH dependent. On longer time scale, the species decayed by a bimolecular process. The presence of O(2) did not affect its decay rate constant. The (•)OH reacts with guanine at pH 4.6 with a diffusion-controlled second order rate constant of ≥1 × 10(10) mol(-1) dm(3) s(-1). The reaction of Br(2)(•-), O(2)(•-), and 2-hydroxy-2-propyl radical with guanine was also investigated to differentiate among the one-electron oxidized, one-electron reduced species of guanine and the guanine-OH adducts formed in the reaction of (•)OH at pH 4.6. On the basis of the spectral characteristics and reactivity toward O(2), two guanine-OH adduct species were identified (i) the C4-OH adduct species absorbing at 330 nm which has not been reported so far and (ii) the C8-OH adduct species absorbing at 300 nm in agreement with the known literature absorption features. Quantum chemical calculations using BHandHLYP with 6-31+G(d,p) basis set and excited state calculations using TDDFT for all possible transients complement the assignment of the observed spectral peak at 330 nm to the C4-OH adduct of guanine. Furthermore, steady state radiolysis revealed the formation of 8-hydroxy-guanine whose precursor is known to be the C8-OH adduct species.

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The radical scavenging ability of malonamides has been explored by use of the pulse radiolysis technique.