Reactive oxygen and nitrogen species (RONS) scavenging reactions of o-vanillin: Pulse radiolysis and stopped flow studies |
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Authors: | Atanu Barik K Indira Priyadarsini Hari Mohan |
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Institution: | (1) Radiation and Photochemistry Division, Bhabha Atomic Research Centre, Trombay Mumbai, 400085, India |
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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 (CCl3O
2
·
) 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. 105 M−1s−1, 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 × 103 M−1s−1. 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−1. 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. |
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Keywords: | o-Vanillin peroxyl radical azide radical stopped flow pulse radiolysis peroxynitrite |
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