Versatile Activity of a Copper(II) Complex Bearing a N₄‐Tetradentate Schiff Base Ligand with Reduced Oxygen Species

Abstract

The reactivity of the Cu(II) complex of N,N'-bis(pyridin-2-ylmethylene)propane-1,3-diamine (py 2 pn), [Cu(py 2 pn)(ClO 4 ) 2 ], toward O 2and H 2 O 2 has been examined. The complex reacts with O 2 *À with fast second order kinetics, k McF = 4.05 × 10 6 M À 1 s À 1 , employing the Cu(II)/Cu(I) couple proved by spectroscopic detection of the reduced form at low temperature. At À 40 °C in DMF, the reaction of the complex with H 2 O 2 /Et 3 N yields an stable end-on Cu(II)-hydroperoxide, with k OOH = 0.31 min À 1 , the formation of which has been established by DFT calculations, electronic and EPR spectra. At room temperature, the end-on Cu(II)-hydroperoxide reacts with a second Cu(II) complex to evolve O 2 , with k CAT = 83.2 M À 2 s À 1 . The Cu(II)-hydroperoxide can mediate phenol oxidation, probably through a trigonal bipyramidal ternary transition state based on DFT analysis, favored over catalase activity when low proportion of catalyst is used. In these reactions, structural constraints imposed by the ligand distort the coordination geometry of the metal and controls reactivity.

Improvement of Peptidyl Copper Complexes Mimicking Catalase: A Subtle Balance between Thermodynamic Stability and Resistance towards H2O2 Degradation

“…A Clark-type electrode can be used to monitor O 2 formation when H 2 O 2 is added to the complex solution (see Figure S5 for representative experiments). The catalase activity of many complexes mimicking CAT has only been studied in organic solvents or at relatively high pH [ 29 , 32 , 35 ], except for a few [ 31 , 35 , 36 , 37 ]. With peptidyl complexes, aqueous solubility at pH around 7 allowed us to conduct studies in more biologically relevant conditions, namely, in aqueous MOPS buffer (50 mM) at pH 7.5.…”

“…So far, the majority of bioinspired mimics have been mononuclear Fe or Mn porphyrinic complexes [ 18 , 23 ], with the ligand porphyrin being easily oxidizable and participating in the bi-electronic exchange, and di-nuclear non-heme Mn complexes [ 17 , 24 ]. A few examples of nanoparticles and metal–organic framework (MOF) nanoparticles have also been identified as CAT mimics [ 25 , 26 ], as well as a few copper complexes [ 27 , 28 , 29 , 30 , 31 , 32 ]. However, their catalytic activity was often reported in organic solvents or at non-physiological pH because of their low solubility in aqueous pH 7.5 conditions or the need for an external base.…”

Effect of Metal Environment and Immobilization on the Catalytic Activity of a Cu Superoxide Dismutase Mimic

“…norganics 2023, 11, x FOR PEER REVIEW form of the enzyme, the Cu(II) ion is bound to the N4-donor set of four hist and one water molecule, adopting a distorted square-pyramidal geometry ion is bridged to the Zn(II) ion through the imidazolate ring from one o residues, and the Zn(II) coordination sphere is completed by two histidine a tate residues disposed in a distorted tetrahedral geometry (Figure 1) [5,6]. In the search for efficient SOD mimics, a number of Cu(II) complexes w ligand scaffolds bearing an N4-donor set have been synthesized and their evaluated [7][8][9][10][11][12][13][14][15][16][17]. During the redox cycle, the switch between Cu(II) and C states involves changes in coordination number and geometry around the from tetragonal to tetrahedral [18,19].…”

“…Results obtained via employing these lization approaches are compared with the intention to ascertain the effe covalent binding of the catalyst on the support of the turnover numbers an covery. In the search for efficient SOD mimics, a number of Cu(II) complexes with nonheme ligand scaffolds bearing an N 4 -donor set have been synthesized and their SOD activity evaluated [7][8][9][10][11][12][13][14][15][16][17]. During the redox cycle, the switch between Cu(II) and Cu(I) oxidation states involves changes in coordination number and geometry around the metal ion, i.e., from tetragonal to tetrahedral [18,19].…”

“…It must be noted that the absence of a re-dissolution peak upon anodic polarization scans indicates that no copper is released from the Cu(I) complex generated at the electrode. For comparison, [Cu(py 2 pn)] 2+ , formed with the Schiff base N,N'-bis(2-pyridylmethylen)propane-1,3-diamine, is reduced at −0.044 V vs. SCE [7]. Therefore, the more flexible N 4 -diamine/dipyridine ligand stabilizes Cu(II) toward reduction better than the N 4 -diimine/dipyridine one, reflecting the higher electron-donor ability of pypapn.…”