Autosensitized Photooxidation of the Rose Hip (Wild Rose) Oil - Mechanism and Quantum Yield for Singlet Molecular Oxygen O2 (1 Δg) Generation

The autosensitized photooxidation of the fatty acid components of rose hip (Wild Rose) oil was studied. Two important facts arise from the present investigation: a) Fatty acids of rose hip oil decompose upon visible light irradiation in the absence of external sensitizers by a mechanism that involves O₂(¹Δ_g). The pigments present in rose hip oil themselves efficiently sensitize the generation of O₂(¹Δ_g) with a quantum yield of 0.038 (upper limit). b) Visible irradiation also produces the degradation of the anthocyanines, native pigments which could behave as O₂(¹Δ_g) sensitizers in the oil. In this case a mechanism involving the production of superoxide ions by the pigment and further attack of the radicals on the phenol groups of the anthocyanine could account for the observed experimental evidences. These results should be carefully considered in a practical sense when rose hip oil is stored or employed under daylight conditions. Exposure to visible radiation may cause irreversible transformations in rose hip oil.