Investigation of oxidation attack sites in sterols: Thermodynamics of hydrogen atom transfer

- The attention is focused on 7 naturally occurring sterols and 15 steroid nuclei.
- OH and CH bond dissociation enthalpies are studied by DFT/B3LYP approach.
- Investigated CH bonds are more labile than OH bonds.
- Sterol nucleus is more susceptible to oxidation than side chain.

B3LYP study of 7 naturally occurring sterols was carried out in terms of OH and CH bond dissociation enthalpies (BDE) to identify thermodynamically favored oxidation attack site. In all compounds, OH BDEs are significantly higher than CH BDEs. Found results showed that sterol nuclei are more susceptible to the oxidation than side chains. Lowest BDE values were found for the C14H bond in the majority of molecules with C14 atom in the α-position to a CC double bond. C5C6C7C8 alternating double bonds cause further drop in C14H BDE. Because the nuclei are responsible for the reported oxidation instability of sterols, 15 various steroid nuclei were also investigated.