New Schiff base complexes, including diamagnetic metal ions (Pd2+/C1, Pt2+/C2, Zn2+/C3), have been synthesized via appropriate conventional methods using 1-phenyl-1-(pyridin-4-ylimino) propan-2-one oxime (PPYO) as a Schiff base ligand. Theoretical studies confirmed that the C1-C3 have high reactivity and pharmacological potential. The antioxidant activity of the C1-C3 was determined using the DPPH (2,2-diphenyl-1- picrylhydrazyl) method and the following trend was obtained: C1 > C2 > C3 > PPYO. These complexes were able to present good cytotoxic effects on HCT116 colon cancer cells. The trend of anticancer activity is as follows: C2 > C1 > C3. Considering the importance of the antioxidant enzyme catalase in removing reactive oxygen species (ROS), the binding process of C1-C3 with catalase was evaluated. The results showed that C1-C3 can inhibit the catalytic performance of catalase. The C1-C3 quenched the catalase fluorescence emission with a static quenching mechanism. The binding affinity to catalase was almost similar for all three complexes (Kb ¼ 6.37 ± 0.33, 3.23 ± 0.14 and 4.57 ± 0.36 × 105 M 1 for C1, C2 and C3, respectively at 303 K). In C1/C2 interaction with catalase, which was an exothermic and spontaneous process, hydrogen bonds, van der Waals forces, and hydrophobic interactions played a decisive role and were strongly confirmed by molecular docking data. Tracking the structural changes of catalase showed that the enzyme undergoes structural changes in the presence of complexes.
