A combined approach of electronic spectroscopy and quantum chemical calculations to assess model membrane oxidation pathways

Abstract

Determining the UV absorbances at 234 nm and 280 nm enables a quick determination of the oxidation progress in lipid membranes. Nevertheless, experimental spectral results indicate a significant overlapping of bands arising from different oxidation products. The calculation of theoretical electronic spectra of the plausible oxidation products can provide strong support for spectral interpretation. The goal of this work was to set up a UV-based method to assess the peroxidation products of lecithin liposomes. UV spectra of liposomes exposed to H₂O₂ and CuSO₄ were recorded and peak-fitted to determine the overlapping bands contributing to the experimental features. Time-dependent density functional theory (TD-DFT) calculations were used to optimize the molecular structures and assess the theoretical UV spectra of all possible oxidation products. Two oxidation routes were considered; one of them regarding the formation of conjugated dienes and the other related to the formation of hydroxy fatty acids. The integrated experimental and theoretical analysis of the UV spectra showed the presence of conjugated dienes M and N in the experimental spectra, occurring at λ_max ≅ 240 nm and fitting well in the band at λ_max ≅ 237 obtained after deconvolution. In turn, compounds A, D, H and I, arising from the hydroxy fatty acid pathway, were those leading to the experimental bands at λ_max ≅ 225, 232 and 244 nm, respectively. The integrative computational and experimental approach conducted in this work provides a better understanding of lipid peroxidation processes.