Salen‑manganese complexes for controlling ROS damage: Neuroprotective effects, antioxidant activity and kinetic studies

A new manganese(III) complex [MnL1(DCA)(H2O)](H2O),1 [H2L1 is the chelating ligand N,N′-bis(2-hydroxy-3-methoxybenzylidene)-1,2-diaminopropane, and DCA is dicyanamide], has been prepared and characterized by different analytical and spectroscopic techniques. The tetragonally elongated octahedral geometry for the manganese coordination sphere was revealed by X-ray diffraction studies for 1. The antioxidant behavior of this complex and other manganese(III)-salen type complexes was tested through superoxide dismutase and catalase probes, and through the study of their neuroprotective effects in SH-SY5Y neuroblastoma cells. In this human neuronal model, these model complexes were found to improve cell survival in an oxidative stress model. During studies aimed to getting a better understanding of the kinetics of the processes involved in this antioxidant behavior, an important effect on the solvent in the kinetics of reaction of the complexes with H2O2 was revealed that suggests a change in the mechanism of reaction of the complexes. The kinetic data in methanol and buffered aqueous solutions correlate well with the results of the test of catalase activity, thus showing that the rate determining step in the catalytic cycle corresponds to the initial reaction of the complexes with H2O2. Salen‑manganese complexes with superoxide dismutase and catalase activity can protect cells from oxidative damage and ameliorate the mitochondrial function in a human neuronal model. Kinetic studies using hydrogen peroxide as oxidant showed a solvent-dependent mechanism, the rate determining step being the initial reaction of the complexes with the substrate. [Display omitted] •A new Mn(III)-Schiff base-dicyanamide catalase mimic has been obtained.•The new salen-Mn(III) and other related complexes show antioxidant activity.•These complexes improve cell survival against oxidative stress in a human neuronal model.•The mechanism of reaction of this type of complex with H2O2 is solvent-dependent.•Catalase cycle: initial reaction of the complexes with H2O2 is the rate determining step.