An antioxidant mechanism of morphine and related derivatives

A structural and computational study of the morphine mechanism as an antioxidant or oxidant compound is performed by density functional theory (DFT) calculations. The geometry was obtained using the B3LYP/6-31G(d,p) method. The antioxidant property of morphine is related to the highest occupied molecular orbital (HOMO) energy, ionization potential (IP), stabilization energy (ΔΕiso), bond dissociation energy (BDE), and spin density distribution for the electron abstraction at the amine position, which is more favored than other positions for morphine. The decrease in the HOMO and IP values, together with the increase in the ΔΕiso values, is related to amine groups, ether and alkyl moieties, benzene rings, hydroxyls, and double bonds. The hydrogen abstraction in the phenol position is more favored than the other positions in morphine. The prevalent spin contribution for these groups is important for the highest stability free radical and other resonance structures. Morphine is more powerful antioxidant than its de-methylated or hydroxylated derivatives.