In the present work, we report the results of a spin trapping ESR study of four essential oils widely used for skin care products such as creams and bath salts. The studied essential oils are Rosmarini aetheroleum (rosemary), Menthae piperitae aetheroleum (mint), Lavandulae aetheroleum (lavender), and Thymi aetheroleum (thyme). Fenton reaction in the presence of ethanol was used to generate free radicals. The N-tert-butyl-α-phenylnitrone (PBN) was used as a spin trap. In the Fenton reaction, the rosemary oil had the lowest effect on radical adduct formation as compared to the reference Fenton system. Since essential oils are known to be lipid soluble, we also conducted studies of essential oils in Fenton reaction in the presence of lipids. Two model lipids were used, namely 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC). The obtained results suggested that in the presence of DOPC lipids, the •OH and PBN/•CHCH3(OH) radicals are formed in both phases, that is, water and lipids, and all the studied essential oils affected the Fenton reaction in a similar way. Whereas, in the DPPC system, the additional type of PBN/X (aN = 16.1 G, aH = 2.9 G) radical adduct was generated. DFT calculations of hyperfine splittings were performed at B3LYP/6-311+G(d,p)/EPR-II level of theory for the set of c-centered PBN adducts in order to identify PBN/X radical.
