Synthesis, Characterization and Combined Superoxide Dismutase and Catalase Activities of Manganese Complexes of 1,4‐Bis(salicylidenamino)butan‐2‐ol

Abstract

Two MnIV complexes of general formula [Mn(salbutO)X] [H3salbutO = 1,4-bis(salicylidenamino)butan-2-ol, 1:X=N3, 2: X = SCN] have been prepared and structurally characterized. The crystal structure of 1 shows that salbutO3– acts as a pentadentate ligand through the two phenolato-O, two imino-N, and one alcoholato-O atoms, and the sixth coordination position is occupied by the azido-N atom, resulting in a slightly distorted N3O3 donor set around the MnIV ion. ESIMS, UV/Vis, and 1H NMR spectroscopy were used for solution studies. In methanol and dmf, the starting complexes are converted into [MnIII(salbutO)] and its dimeric form. The E1/2 of MnIII/MnIV (ca. 0.4 V vs. Ag/AgCl) allows this couple to efficiently catalyze the dismutation of O2 ·– with catalytic rate constant and IC50 values of 1.91 106 M–1 s–1 and 1.43 µM, respectively, which were obtained through the nitro blue tetrazolium photoreduction inhibition SOD assay, in aqueous solution of pH 7.8. The Mn-salbutO complexes also show catalase activity in methanol and dmf, with kcat = 1.6 M–2 s–1 and 5.6 M–1 s–1, respectively, an advantageous property for acting as scavenger of reactive oxygen species (ROS). This valuable conjunction of properties results from the conversion of [MnIV(salbutO)X] into [MnIII(salbutO)]2 in equilibrium with its monomer [MnIII(salbutO)].