Cobalt(II), Zinc(II), Iron(III), and Copper(II) Complexes Bearing Positively Charged Quaternary Ammonium Functionalities: Synthesis, Characterization, Electrochemical Behavior, and SOD Activity

Abstract

We have synthesized and characterized Co(II) (1), Zn(II) (2), Fe(III) (3) and Cu(II) (4) complexes of 2,2'‐[2,6‐pyridinediylbis(ethylidyne‐1‐hydrazinyl‐2‐ylidene)]bis[N,N,N‐trimethyl‐2‐oxoethanaminium] dichloride (H2LCl2) by NMR, IR, and X‐Band EPR spectroscopy, respectively, as well as by single‐crystal X‐ray structural analysis. H2LCl2 belongs to the class of diacetylpyridine bis(hydrazone) ligands and bears two positively charged quaternary ammonium functionalities. The complexes 1–3 possess a pentagonal‐bipyramidal geometry, whereas 4 has square‐pyramidal geometry. Redox reactivity and SOD activity of the complexes was studied by means of electrochemical measurements in aqueous‐buffer and DMF or DMSO solutions, respectively, as well as by stopped‐flow measurements. Complexes 1–3 do not have SOD activity, whereas 4 exhibits a high catalytic rate constant for the superoxide dismutation, kcat = 1.73 × 107 m–1 s–1 (in MOPS buffer solution of pH = 7.4). The results were discussed in terms of complex redox potentials, electrostatic interactions and their spatial distribution, kinetic lability of metal centers, and stability of peroxo intermediates, respectively.

New Insights into the Physicochemical and Electrochemical Characterization of Gold Phthalocyanine-Based Materials

“…While the redox pair C 1 /C 2 -C 2 ' is attributed to the behavior of gold (oxidation in C 1 and reduction in C 2 -C 2 '), the unexpected redox pair A 1 '/A 2 ' could be the trace amount of dissolved oxygen. 71 Similar to the above discussion in aqueous media, 32,61,[69][70][71] we hypothesize that the other observed redox A 1 /A 2 and B 1 /B 2 -B 2 ' peaks are due to the phthalocyanine ring reduction and oxidation, AuPc/[AuPc] − , [AuPc] − /[AuPc] 2− and [AuPc] 2− /[AuPc] 3− . The discrepancy in the behavior of redox processes between aqueous and non-aqueous electrolytes could be explained by competitive HER in aqueous media that reduce the potential window where we could observe all redox processes.…”

“…7f and S16) demonstrates that the electrochemical process is in a mixed regime of adsorption and diffusion. [66][67][68] Leveraging on the existing electrochemistry literature of other metallophthalocyanines 32,61,[69][70][71] and gold porphyrin, 21,22 8a-8c where the "blank" refers to the absence of compound. In order to rationally assign the different redox processes, we performed control experiments using a bare gold electrode, which is reported in Fig.…”

Copper(II) Complexes of Pyridine-2,6-dicarboxamide Ligands with High SOD Activity

“…17 Moreover, the metal complexes of diacetylpyridinebis(hydrazone) type ligands exhibit remarkable superoxide dismutase (SOD) activity. 20 Up to date, pyridine-based pentaazamacrocyclic ligands are one of the most prominent classes of non-peptidyl SOD mimetics. 21 SODs are a dedicated class of enzymes which are required to keep the concentration of the superoxide anion radical under a controlled low limit via the disproportionation of superoxide anion to molecular oxygen and hydrogen peroxide.…”

“…33 Earlier studies revealed that the presence of positively charged groups (arginine moieties, quaternary ammonium groups) facilitates the interaction with the superoxide anion and significantly affects the SOD activity. 20,32 In addition to positively charged groups, the hydroxyl groups are also capable of altering the SOD activity. 34 In the iron, manganese, or nickel containing SOD enzymes, the role of the phenolic hydroxyl group of the tyrosine residue has clearly been confirmed.…”

“…Thus, these complexes are excellent models of oxygenase enzymes . Moreover, the metal complexes of diacetylpyridine-bis­(hydrazone) type ligands exhibit remarkable superoxide dismutase (SOD) activity . Up to date, pyridine-based pentaazamacrocyclic ligands are one of the most prominent classes of non-peptidyl SOD mimetics …”