A 7-COORDINATE MANGANESE(II) COMPLEX FORMED WITH A SINGLE TRIPODAL HEPTADENTATE LIGAND AS A NEW SUPEROXIDE SCAVENGER

A new manganese(II) complex, Mn(II)-tris[2-[N-(2-pyridylmethyl)amino] (Mn-TPAA), has been synthesized, its X-ray crystal structure resolved, and its superoxide stoichiometric scavenging activity established. Th e complex has been formed with the tripodal potentially heptadentate l igand TPAA which turns out to be the single ligand coordinated to the metal ion and therefore achieves the seven coordination. The complex c rystallizes in the space group P2(1)2(1)2(1), a = 19.654(9) Angstrom, b = 15.416(5) Angstrom, c = 10.425(4) Angstrom, with four formula unit s per unit cell. The manganese is bonded to three pyridine nitrogen at oms, to three amine groups, and to the tripodal bridging nitrogen N. T he reactivity toward superoxide has been investigated using the indire ct xanthine-xanthine oxidase-cytochrome c method, the electrochemical reaction of in-situ generated superoxide, and gamma and pulse radiolys is measurements. From the cytochrome c assay, it has been found that t he IC50 value is equal to 4.4 mu M. From electrochemical experiments p erformed in dry acetonitrile and in the presence of oxygen, the comple x appears to induce the one-electron reduction of oxygen to split into two separate steps. Electrochemistry also shows that superoxide react s with the complex. Confirmation of this reaction is obtained with pul se radiolysis which allows the observation of a transient, visualized by its difference absorption spectrum, with a rate constant of 1.05 x 10(7) M(-1) s(-1). Inhibition of the formation of H2O2 is also found.