Characterization of free fatty acids photo‐oxidation under UV radiations: A stepwise Raman study

Ali Assi (1) , Rime Michael‐jubeli (1) , Arlette Baillet‐guffroy (1) , Ali Tfayli (1)

1 Lip(Sys)² - Lipides : systèmes analytiques et biologiques

Abstract Lipid peroxidation (LPO) is an oxidative deterioration when oxidants such as reactive oxygen species attack lipids that contain double bonds especially polyunsaturated fatty acids (PUFAs). The mechanism of LPO is composed of three steps: initiation, propagation, and termination. It can result from several reaction pathways: (1) auto‐oxidation, (2) enzymatic oxidation, or (3) photo‐oxidation. UV solar exposition is a major concern in skin research, dermatology, and cosmetic science. Skin surface lipids (SSLs) and stratum corneum (SC) lipids are among the first skin components exposed to external insults such as UV radiations. Fatty acids represent a major lipid class in SSLs and SC. The aim of this paper is to study the photo‐oxidation of fatty acids under UV solar radiations using Raman spectroscopy. Vibrational spectroscopies are useful techniques to follow the LPO in its different stages of oxidation: (1) the initiation step by following the CH 2 /CH 3 stretching bands ratio that decreases due to the hydrogen abstraction in alpha position; (2) the propagation step where primary oxidation products are formed such as hydroperoxides, which was evaluated by following the 1165/1640 cm −1 ((δ(OH) and ν(CO))/ν(CO)) ratio that increases during oxidation process; and finally, (3) the termination step that is marked by the formation of aldehydes, alcohols, ketone, trans secondary oxidation products, and others, which was monitored by following the 1730/1640 cm −1 (ν(CO) (ald.)/ν(CO) (acid)) ratio and the trans ν(CC)/ cis ν(CC) ratio that increase indicating the formation of secondary oxidation products. To our knowledge, this work is the first to put together different spectral descriptors enabling to follow, step by step, the different modifications of free fatty acids structures during the oxidation process.

Mots clés: LPO: Lipid peroxidation. MDA: Malondialdehyde Palmitic acid Fatty acids Lipid Peroxidation Solar radiation Vibrational spectroscopy Malondialdehyde; LPO: Lipid peroxidation. MDA: Malondialdehyde Palmitic acid Fatty acids; Lipid Peroxidation; Solar radiation; Vibrational spectroscopy; Malondialdehyde; LPO: Lipid peroxidation. MDA: Malondialdehyde Palmitic acid Fatty acids Lipid Peroxidation Solar radiation Vibrational spectroscopy Malondialdehyde

Domaines: Chimie

Ali Assi, Rime Michael‐jubeli, Arlette Baillet‐guffroy, Ali Tfayli. Characterization of free fatty acids photo‐oxidation under UV radiations: A stepwise Raman study. Journal of Raman Spectroscopy, 2022, 54 (1), pp.24-36. ⟨10.1002/jrs.6449⟩. ⟨hal-04528003⟩