Theoretical study on the chemical fate of adducts formed through free radical addition reactions to carotenoids
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It is well known that free radicals are responsible for oxidative stress and cause numerous health disorders. As a result, the study of molecules that can scavenge free radicals is significant. One of the most important classes of free radical scavengers are carotenoids (CAR). In this work, the effectiveness of the CAR in terms of the radical adduct formation (RAF) reaction is studied using density functional theory calculations (in polar and non-polar environments). The reactions between four CAR [β-carotene (BC), zeaxanthin (ZEA), canthaxanthin (CANTA) and astaxanthin (ASTA)] with eight different radicals (•OH, •OOH, •CH3, •O–CH3, •OO–CH3, •SH, •O–CH2–CH=CH2, and •OO–CH2–CH=CH2), as well as substantial further reactions involved in the radical chain propagation, are analyzed. According to our results, the RAF reactions are controlled to a larger extent by the nature of the free radical than by the particular CAR they are reacting with. Thermochemistry calculations predict that each CAR molecule is able to scavenge at least two free radicals, which would lead to the termination of the radical chain process. Epoxy and diepoxy CAR species can be formed, being epoxy molecules as good free radical scavengers as their parent CAR. ASTA and CANTA are predicted to be less reactive, when reacting through RAF mechanism, than BC and ZEA.
KeywordsCarotenoids Radical reactions Computational chemistry Antioxidants Thermochemistry
This study was made possible due to funding from the Consejo Nacional de Ciencia y Tecnología (CONACyT), as well as resources provided by the Instituto de Investigaciones en Materiales IIM, UNAM. The work was carried out, using a KanBalam supercomputer, provided by DGSCA, UNAM and the facilities at Laboratorio de Supercómputo y Visualización en Paralelo of UAM Iztapalapa. The authors would like to acknowledge both Oralia L. Jiménez A and María Teresa Vázquez for their technical support. A.M. is grateful for financial support from DGAPA-UNAM-México, and R.V. for the financial support from CONACYT, through project 49057-F.
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