Gamma‐irradiation of 7‐ketocholesterol in aqueous dispersions and liposomes

7‐Ketocholesterol in aqueous sodium stearate dispersions or incorporated into liposomes was exposed to gamma radiation at 0–4°C to a dose of 50 kGy. Substrate degradation was noted in all systems, but occurred to a much greater extent in dispersions (≈90%) than in liposomes (0–25%). The difference in degree of degradation is attributed to dissimilarities in the micro‐environment of 7‐ketocholesterol in the two systems. The principal decomposition product was identified as 7‐ketocholestanol, a compound that can arise from hydrogenation of the double bond of the starting material. Also detected, but in lower concentration, were the epimeric 7‐hydroxycholesterols resulting from the reduction of the original carbonyl function. Both 7‐ketocholestanol and the epimeric 7‐hydroxycholesterols are believed to be secondary species generated by the interaction of the starting material with the primary radiolysis products of water. In addition, many minor degradation products were noted but not identified.