A new type of manganese-Schiff base complex, catalysts for the disproportionation of hydrogen peroxide as peroxidase mimics

Abstract

New manganese(II) and manganese(III) complexes of substituted N,N 0 -bis(salicylidene)-1,2-diimino-2methylethane have been prepared and characterized. Elemental analysis, IR and EPR spectroscopies, mass spectrometry, magnetic measurements and the study of their redox properties have confirmed their respective formulae as Mn II L(H 2 O) 2 and Mn III L(H 2 O) n (ClO 4 ). Electron-withdrawing substituents on the phenyl rings of the ligand stabilize the oxidation state (II) for manganese, but the electron-donating substituents on the Schiff bases are those that lead to Mn(III) complexes, which behave as efficient peroxidase mimics in the presence of the water-soluble trap ABTS. The rate of peroxidase activity of the present complexes is significantly higher than that of other series of Mn-Schiff base compounds, probably due to their versatility in adopting in solution a structure that allows the coordination of the hydrogen peroxide substrate molecule to the manganese.

Biomimetic Catalysts for Oxidation of Veratryl Alcohol, a Lignin Model Compound

“…174.32 (7) O10-Mn1-N41 94.00(7) O10-Mn1-O1w 90.66 (7) O30-Mn1-O1w 90.11 (6) The axial positions of the octahedron are occupied by a capping water molecule and a dicyanamide molecule. The Jahn-Teller elongation expected for d 4 high-spin manganese(III) appears outstanding in the axis orthogonal to the plane of the Schiff base ligand, with distances ranging from 2.26 to 2.30 Å, considerably longer than the equatorial Mn-O bond lengths quoted earlier [12][13][14][15].…”

“…In our search of biomimetic models for peroxidase, we have also reported active manganese complexes involving tetradentate ONNO Schiff bases, and the influence of the geometry around the manganese ion on peroxidase activity has also been studied by us [12][13][14].…”

Structure and Heme-Independent Peroxidase Activity of a Fully-Coordinated Mononuclear Mn(II) Complex with a Schiff-Base Tripodal Ligand Containing Three Imidazole Groups

“…EPR experimental conditions: microwave frequency, 9.22 GHz; modulation amplitude, 5 G; modulation frequency, 100 kHz; time constant, 0.3 sec; scan time, 4 minutes; and temperature, 110 K. 650, 740, and 835 nm while the reduced form, ABTS, is colorless. [7][8][9]22,28 Peroxidase-like reaction was initiated by adding 1 mL of the methanolic solution of complex 1 (1.5 × 10 -9 mol of…”

“…7,8 They suggested that highly symmetric environments of the metal center could dimerize by itself or via exogenous axial ligand during the catalytic process, fulfilling the requirements of the peroxidase activity. [7][8][9] Guilherme et al recently reported a mononuclear manganese(II) complex, fully-coordinated by two N,N-bis (2-pyridylmethyl)amine (bmpa) ligands, to exhibit catalase-like function. 10 The authors proposed that one of the two pyridyl groups in one of two bmpa ligands was labile to form a high valent Mn(IV)=O intermediate or to form a dimer bridged by a hydrogen peroxide for the catalytic process.…”

Synthesis and Physicochemical Properties of Schiff Base Macrocyclic Ligands and Their Transition Metal Chelates

“…1 For example, manganese complexes involving tetradentate Schiff base derivatives are most versatile and interesting synthetic systems. 2 Some of these types of complexes were found to be artificial mimics of the biological enzymes such as Mncatalase, 3 Mn-superoxide dismutase, Mn-ribonucleotide reductase and in particular, the Mn-peroxidase that protects cells against hydrogen peroxide induced oxidative stress. It has been observed that the catalytic activity of the Schiff base complexes is very sensitive to minor structural changes.…”