Synthesis and antioxidant properties of dicationic ionic liquids

Hydroxyl functionalized ammonium dicationic ionic liquids containing naturally derived ions and ether linkage between cationic head groups were synthesized and described as a novel form of antioxidant. A simple neutralization reaction with protocatechuic and gentisic acids as the source of anions was used for the preparation of ionic liquids. All compounds were characterized in terms of phase transitions and thermal stability via differential scanning calorimetry and thermogravimetric analysis techniques. In addition, the structures of salts were confirmed by nuclear magnetic resonance spectroscopy. Antioxidant activity was evaluated using free radical quenching and reducing power assays as well as lipid peroxidation inhibition. The studies confirmed that the obtained dicationic ionic liquids with 3,4- or 2,5-dihydroxybenzoate anions exhibit significant radical scavenging activity or reducing power. The results were better than those obtained with commonly used antioxidants, such as Trolox. However, only the protocatechuate DILs exhibited linoleic acid peroxidation inhibition.