Mn and Cu complexes of a novel malic acid–cysteine ligand with remarkable ROS scavenging activity†

The scientific community is very interested in investigating antioxidant activity using various assays to treat oxidative stress and reduce the harmful effects of free radicals. Cysteine, a sulfur-containing compound can treat oxidative stress. The primary objective of this study was to create a novel ligand through the combination of L-cysteine with malic acid and its metal complexes with copper and manganese. The following discussion focuses on how the complexes mimic natural antioxidant enzymes and explains how they could be used to remove reactive oxygen species. Various methods were used to verify the synthesis, including FT-IR, UV-vis, TGA, CHNS, EDX, SEM, mass, and fluorescence. These techniques indicated structural changes upon complexation and integration with β-CD. Spectrophotometric tests were used to evaluate the compounds' peroxidase-, catalase-, and superoxide dismutase-like activities under different conditions. Cytotoxicity was evaluated using HFF-2 cells and the MTT test. The amounts of carbon, hydrogen, nitrogen, and sulfur were 39.48, 4.7, 6.58, and 15.23, and the ligand formula is C₇H₁₁NSO₆. Changes in infrared spectral signals upon metal interaction, particularly in the carboxylate region, indicate significant metal–ligand bonding. The results showed that the β-CD-modified complexes, especially Cu-complex/β-CD and Mn-complex/β-CD, had better antioxidant activity (91% and 78%, respectively). They were better at scavenging O₂˙⁻ radicals and breaking down H₂O₂ into safe byproducts. Additionally, Mn-complex/β-CD was less cytotoxic. In conclusion, the produced complexes are promising antioxidants and potential treatments for diseases linked to oxidative stress, especially the β-CD derivatives.