Efficient scavenging of β-carotene radical cations by antiinflammatory salicylates

Abstract

The radical cation generated during photobleaching of β-carotene is scavenged efficiently by the anion of methyl salicylate from wintergreen oil in a second-order reaction approaching the diffusion limit with k₂ = 3.2 × 10⁹ L mol⁻¹ s⁻¹ in 9 : 1 v/v chloroform–methanol at 23 °C, less efficiently by the anion of salicylic acid with 2.2 × 10⁸ L mol⁻¹ s⁻¹, but still of possible importance for light-exposed tissue. Surprisingly, acetylsalicylate, the aspirin anion, reacts with an intermediate rate in a reaction assigned to the anion of the mixed acetic–salicylic acid anhydride formed through base induced rearrangements. The relative scavenging rate of the β-carotene radical cation by the three salicylates is supported by DFT-calculations.