The following presentation is based on experimental work we have already developed and published. We investigated the nitrogen oxides in different solvents and analyzed their reaction with β‐carotene. The electron paramagnetic resonance spectroscopy (EPR) and ultraviolet and visible (UV‐vis) spectroscopy were applied to investigate the reaction of β‐carotene with nitrogen dioxide and nitric oxide in both pure dioxane and dioxane/water solvent. Free radicals were detected and evaluated with the EPR technique, which is highly selective and sensitive. A reaction mechanism was proposed on the basis of the experimental kinetic and EPR results. The validity of the mechanism was checked by applying simulation set up conditions that reproduced the results achieved. The radical intermediates proposed in the reaction: the β‐carotene neutral radicals and the cyclic nitroxide neutral radicals were theoretically studied. For that purpose, the density functional theory (DFT) level was applied, selecting the most suitable method, the unrestricted Becke‐style 3‐parameter with the Lee‐Yang‐Parr correlation functional (UB3LYP) and the 6‐31G(d) basis sets (d orbital functions). We developed an appropriate discussion on the importance of carotenoids compounds and their reactions in biological media. Also, we evaluated the role and the possible reactions of nitroxide intermediates.
Part of the book: Carotenoids