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.…”

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.…”

Synthesis of Zn( ii ) coordination complexes, their molecular design and docking with SARS-CoV-2 RBD protein and Omicron spike protein

“…Such a type of electrochemistry behaviour for the Zn( ii ) complexes has also been reported in the literature. 69…”

Highly active superoxide dismutase mimic: pyridine carboxamide-based copper( ii ) complexes

“…The excellent SOD activity was determined by considering the interaction between the superoxide anion and the hydroxyl group of tyrosine, which promotes the binding of the superoxide anion to the metal center and enhances the proton transfer in the dismutation cycle. Earlier studies have also shown that positively charged substituents (cationic Mn( iii ) porphyrins, 13 cationic polyarginine peptides 14 or transition-metal complexes with positively charged quaternary ammonium functions 15 ) of the SOD mimics facilitate the electrostatic interaction with the superoxide anion and increase the SOD activity of the complexes. An in-depth investigation of the characteristics of complexes formed with more dedicated ligands is essential to understand how the structure and composition of the ligands modulate the catalytic activity of SOD mimics.…”

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.…”

Synthesis of Zn( ii ) coordination complexes, their molecular design and docking with SARS-CoV-2 RBD protein and Omicron spike protein

“…Such a type of electrochemistry behaviour for the Zn( ii ) complexes has also been reported in the literature. 69…”

Highly active superoxide dismutase mimic: pyridine carboxamide-based copper( ii ) complexes

“…The excellent SOD activity was determined by considering the interaction between the superoxide anion and the hydroxyl group of tyrosine, which promotes the binding of the superoxide anion to the metal center and enhances the proton transfer in the dismutation cycle. Earlier studies have also shown that positively charged substituents (cationic Mn( iii ) porphyrins, 13 cationic polyarginine peptides 14 or transition-metal complexes with positively charged quaternary ammonium functions 15 ) of the SOD mimics facilitate the electrostatic interaction with the superoxide anion and increase the SOD activity of the complexes. An in-depth investigation of the characteristics of complexes formed with more dedicated ligands is essential to understand how the structure and composition of the ligands modulate the catalytic activity of SOD mimics.…”

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.…”

Synthesis of Zn( ii ) coordination complexes, their molecular design and docking with SARS-CoV-2 RBD protein and Omicron spike protein

“…Such a type of electrochemistry behaviour for the Zn( ii ) complexes has also been reported in the literature. 69…”

Highly active superoxide dismutase mimic: pyridine carboxamide-based copper( ii ) complexes

“…The excellent SOD activity was determined by considering the interaction between the superoxide anion and the hydroxyl group of tyrosine, which promotes the binding of the superoxide anion to the metal center and enhances the proton transfer in the dismutation cycle. Earlier studies have also shown that positively charged substituents (cationic Mn( iii ) porphyrins, 13 cationic polyarginine peptides 14 or transition-metal complexes with positively charged quaternary ammonium functions 15 ) of the SOD mimics facilitate the electrostatic interaction with the superoxide anion and increase the SOD activity of the complexes. An in-depth investigation of the characteristics of complexes formed with more dedicated ligands is essential to understand how the structure and composition of the ligands modulate the catalytic activity of SOD mimics.…”