Author: Saifunneesa Thelakkadan, Muhammed Basheer Ummathur

DOI: http://doi.org/10.31788/RJC.2026.1918560

The antioxidant activity of nine unsaturated β-ketoesters and their Cu(II) complexes was evaluated by the DPPHradical scavenging method. Compounds bearing phenolic –OH groups exhibited higher radical scavenging activity, which increased with both the number of –OH groups and the degree of electron delocalisation. Among the ligands, HL 2 , HL 3 , HL 6 , and HL 8 exhibited notable activity in the order HL 2 > HL 3 > HL 6 > HL 8 . Coordination with Cu(II) further enhanced antioxidant efficiency, attributed to the [CuL₂] stoichiometry that doubles the active phenolicsites and enables Cu(II)/Cu(I) redox cycling. Steric effects also influenced radical-scavenging capacity, emphasisingthe critical roles of phenolic substitution and metal complexation in modulating antioxidant efficacy. The studyprovides insights into structure–activity relationships in synthetic curcuminoid analogues and highlights β-ketoester- based metal complexes as promising antioxidant agents, supporting Sustainable Development Goal 3 (Good Healthand Well-being) by contributing to the development of potential therapeutic antioxidants.

Keywords: Unsaturated β-ketoesters, Cu(II) Complexes, Phenolic Hydroxyl Groups, Antioxidant Activity, DPPHMethod, Structure–Activity Relationship, Curcuminoid Analogues.