Interaction of Astaxanthin with Iron Salts Fe2+ and Fe3+ in Organic Solvents

The carotenoid astaxanthin has a variety of biological activities and antioxidant properties. Due to its lipophilic nature, astaxanthin can be used to protect against lipid peroxidation, in which iron ions play an important role. The effect of Fe²⁺ ions on the oxidative degradation of astaxanthin in phospholipid liposomes was previously studied. In this paper, we study the interaction of astaxanthin with Fe³⁺ and Fe²⁺ in organic solvents of various polarities in the absence of lipids. It is shown that in the presence of Fe³⁺, astaxanthin oxidation and degradation occurs in methanol and dichloromethane. The formation of an intermediate product with an absorption maximum at 876 nm is recorded spectrophotometrically. Electron paramagnetic resonance (EPR) proves the radical nature of the intermediate product, whose signal intensity decreased over time, with the signal remaining for up to 3 days. Based on the obtained results, it can be assumed that the radical product formed in the reaction with Fe³⁺ is the radical cation of astaxanthin. At the same time, no changes are detected when astaxanthin is incubated with Fe²⁺: the absorption spectrum does not change and no radical product is formed.