Spectroscopic and Computational Studies of a Small-Molecule Functional Mimic of Iron Superoxide Dismutase, Iron 2,6-Diacetylpyridinebis(semioxamazide)

Abstract

Fe-dapsox [dapsox=2,6-diacetlypyridinebis(semioxamazide)] is a heptacoordinate pentagonal bipyramidal, functional mimic of iron-dependent superoxide dismutase that has been well characterized on the basis of kinetics and mechanistic studies; however, prior to our studies, its electronic structure had yet to be examined. This paper details our initial characterization of Fe-dapsox in both its reduced and oxidized states, using electronic absorption (Abs) and low temperature magnetic circular dichroism spectroscopies. Density functional theory (DFT) geometry optimizations have yielded models in good agreement with the published crystal structures. Time-dependent DFT and INDO/S-CI calculations performed on these models successfully reproduce the experimental Abs spectra and identify intense, low energy transitions in the reduced complex (FeII(H2dapsox)) as metal-to-ligand charge transfer transitions, suggesting the presence of π-back-bonding in this complex. This back-bonding along with the proton uptake accompanying metal ion reduction provide a compelling mechanism by which the metal-centered redox potential is correctly tuned for catalytic superoxide disproportionation.

Synthesis, characterization and crystal structures of two pentagonal-bipyramidal Fe(III) complexes with dihydrazone of 2,6-diacetylpyridine and Girard's T reagent. Anticancer properties of various metal complexes of the same ligand

“…Pentagonal-bipyramidal complexes of 2,6-diacetylpyridine bis(acylhydrazone) ligands have a wide spectrum of biological activities: cytotoxic [11], antimicrobial [9,10,13], SOD mimetic [14][15][16], DNA/RNA binding and nuclease activity [8,17,18]. In the previously published papers [19][20][21], synthesis, characterization and antimicrobial activity of 2,2'- [2,6-pyridinediylbis(ethylidyne-1-hydrazinyl-2-ylidene)]bis[N,N,N-trimethyl-2-oxoethanaminium] dichloride (H2LCl2) and its corresponding Mn(II) (1), Ni(II) (2), Co(II) (3 and 4), Zn(II) (5) and…”

Role of Spin State and Ligand Charge in Coordination Patterns in Complexes of 2,6-Diacetylpyridinebis(semioxamazide) with 3d-Block Metal Ions: A Density Functional Theory Study

“…22,23,25,60 Because these complexes represent mimics of superoxide dismutase (SOD) and ditopic receptors for lithium salts, they are of the utmost importance, and hence detailed kinetic and mechanistic experimental studies were reported previously. 29 2 ] n+ , explaining the nature of correctly tuned redox potentials in catalytic superoxide disproportionation.…”

Synthesis of Schiff Bases Compounds from Oxamic Hydrazide: Spectroscopic Characterization, X–ray Diffraction Structure and Antioxidant Activity Study

“…Potentially ditopic Schiff bases prepared from oxamic or thioxamic hydrazide have been widely reported in the literature by chemists and in particular those interested in coordination chemistry [1][2][3][4][5][6]. Oxamic hydrazide has two different arms.…”

“…Schiff's bases are synthesized from oxamic hydrazide and used for the preparation of complexes with transition metal and lanthanide ions [9,[22][23][24][25]. The properties of these complexes are evaluated in superoxide catalysis [2,3] and magnetism [26]. It is in this perspective that we have studied these types of ligands and reported their transition metal complexes [7,27].…”