Res. Chem. Intermed.
, Vol. 32, No. 9, pp. 837–845 (2006)
Also available online - www.brill.nl/rci
Reactive oxygen and nitrogen species (RONS) scavenging
reactions of o-vanillin: pulse radiolysis and stopped ﬂow
, K. INDIRA PRIYADARSINI and HARI MOHAN
Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay,
Received 5 June 2006; accepted 10 August 2006
Abstract—Reactions of peroxyl radicals and peroxynitrite with o-vanillin (2-hydroxy 3-methoxy
benzaldehyde), a positional isomer of the well-known dietary compound vanillin, were studied to
understand the mechanisms of its free radical scavenging action. Trichloromethylperoxyl radicals
) were used as model peroxyl radicals and their reactions with o-vanillin were studied using
nanosecond pulse radiolysis technique with absorption detection. The reaction produced a transient
with a bimolecular rate constant of approx. 10
, having absorption in the 400–500 nm region
with a maximum at 450 nm. This spectrum looked signiﬁcantly different from that of phenoxyl
radicals of o-vanillin produced by the one-electron oxidation by azide radicals. The spectra and
decay kinetics suggest that peroxyl radical reacts with o-vanillin mainly by forming a radical adduct.
Peroxynitrite reactions with o-vanillin at pH 6.8 were studied using a stopped-ﬂow spectrophotometer.
o-Vanillin reacts with peroxynitrite with a bimolecular rate constant of 3 × 10
. The reaction
produced an intermediate having absorption in the wavelength region of 300–500 nm with a absorption
maximum at 420 nm, that subsequently decayed in 20 s with a ﬁrst-order decay constant of 0.09 s
The studies indicate that o-vanillin is a very efﬁcient scavenger of peroxynitrite, but not a very good
scavenger of peroxyl radical. The reactions take place through the aldehyde and the phenolic OH
group and are signiﬁcantly different from other phenolic compounds.
Keywords: o-Vanillin; peroxyl radical; azide radical; stopped ﬂow; pulse radiolysis; peroxynitrite.
Phenolic compounds are among the most widely distributed plant products found
in vegetables, fruits, nuts, spices, etc. The ability of phenolic compounds to
act as antioxidants has recently been recognised and a number of low-molecular-
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