A new article published in Photochemical and Photobiological Sciences stated that menthyl anthranilate (MA, tradename meradimate) is a UV-A absorber—interactions of ground-state molecular oxygen with the long-lived triplet state of MA produce singlet oxygen through energy transfer.

The authors reported that the quantum yield of singlet oxygen generation is 0.12 in air-saturated ethanol. Fluorescence and transient absorption measurements suggest that Trolox – a water-soluble analogue of vitamin E and a quencher of singlet oxygen, and α-tocopherol – vitamin E, a natural antioxidant, quench the lowest excited singlet and triplet states of MA. As a result, Trolox and α-tocopherol suppress MA-photosensitized singlet oxygen generation.

Additionally, the suppression of singlet oxygen generation is the mechanism of antioxidant properties of Trolox and α-tocopherol for MA. The ability of α-tocopherol to suppress the MA-photosensitized singlet oxygen generation in isododecane – a solvent for an oil-soluble UV absorber, is close to that in ethanol.

This article summarized that the suppression of sunscreen-photosensitized singlet oxygen generation is an important method for the formulation of safe cosmetic sunscreens.

Source: Photochemical and Photobiological Sciences. 2020 Jun 2. doi: 10.1039/d0pp00023j.