Oxidation of sterols: Energetics of C–H and O–H bond cleavage

Abstract

Abstract Phytosterols, as components of human diet, received much attention because of their cholesterol-lowering and antioxidant properties. We have theoretically studied sterols oxidation in terms of O–H and C–H bond dissociation enthalpies (BDE). In 17 Δ 5 - and Δ 7 -sterols, BDEs were obtained for reported sites of oxidation attack. Obtained results indicate that Δ 7 -sterols are more susceptible to oxidation attack in comparison to Δ 5 -sterols. In sterol nuclei, the lowest BDE was found for C7–H bond in Δ 5 -sterols and for C14–H in Δ 7 -sterols. When Δ 5 -sterol has a C C double bond in the side chain, the lowest BDEs are usually found for C–H bonds in α-positions to this bond. The homolytic cleavage of hydroxyl O–H bond requires larger energy in comparison to the studied C–H bonds. We have shown that the C–H bonds with lowest BDE values actually correspond to the dominant sites of oxidation attack.