Radical Pathway in Catecholase Activity with Zinc-Based Model Complexes of Compartmental Ligands
| Autor: | Averi Guha, Somen Goswami, Debasis Das, Tapan Kumar Mondal, Madhuparna Mukherjee, Ennio Zangrando, Tanmay Chattopadhyay, Nanda D. Paul |
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| Přispěvatelé: | Averi, Guha, Tanmay, Chattopadhyay, Nanda Dulal, Paul, Madhuparna, Mukherjee, Somen, Goswami, Tapan Kumar, Mondal, Zangrando, Ennio, Debasis, Das |
| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: |
Structure analysis
Free Radicals Pyridines Catechols chemistry.chemical_element Zinc Thiophenes Crystallography X-Ray Ligands Medicinal chemistry Catalysis Piperazines Inorganic Chemistry chemistry.chemical_compound Biomimetic Materials Coordination Complexes Pyridine Thiophene Benzene Derivatives Benzoquinones Organic chemistry Phenol Physical and Theoretical Chemistry zinc complex catalysis Molecular Structure Electron Spin Resonance Spectroscopy Substrate (chemistry) Kinetics chemistry Spectrophotometry Quantum Theory Methanol Oxidation-Reduction Catechol Oxidase |
| Popis: | Four dinuclear and three mononuclear Zn(II) complexes of phenol-based compartmental ligands (HL(1)-HL(7)) have been synthesized with the aim to investigate the viability of a radical pathway in catecholase activity. The complexes have been characterized by routine physicochemical studies as well as X-ray single-crystal structure analysis: [Zn(2)(H(2)L(1))(OH)(H(2)O)(NO(3))](NO(3))(3) (1), [Zn(2)L(2)Cl(3)] (2), [Zn(2)L(3)Cl(3)] (3), [Zn(2)(L(4))(2)(CH(3)COO)(2)] (4), [Zn(HL(5))Cl(2)] (5), [Zn(HL(6))Cl(2)] (6), and [Zn(HL(7))Cl(2)] (7) [L(1)-L(3) and L(5)-L(7) = 2,6-bis(R-iminomethyl)-4-methylphenolato, where R= N-ethylpiperazine for L(1), R = 2-(N-ethyl)pyridine for L(2), R = N-ethylpyrrolidine for L(3), R = N-methylbenzene for L(5), R = 2-(N-methyl)thiophene for L(6), R = 2-(N-ethyl)thiophene for L(7), and L(4) = 2-formyl-4-methyl-6-N-methylbenzene-iminomethyl-phenolato]. Catecholase-like activity of the complexes has been investigated in methanol medium by UV-vis spectrophotometric study using 3,5-di-tert-butylcatechol as model substrate. All complexes are highly active in catalyzing the aerobic oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to 3,5-di-tert-butylbenzoquinone (3,5-DTBQ). Conversion of 3,5-DTBC to 3,5-DTBQ catalyzed by mononuclear complexes (5-7) is observed to proceed via formation of two enzyme-substrate adducts, ES1 and ES2, detected spectroscopically, a finding reported for the first time in any Zn(II) complex catalyzed oxidation of catechol. On the other hand, no such enzyme-substrate adduct has been identified, and 3,5-DTBC to 3,5-DTBQ conversion is observed to be catalyzed by the dinuclear complexes (1-4) very smoothly. EPR experiment suggests generation of radicals in the presence of 3,5-DTBC, and that finding has been strengthened by cyclic voltammetric study. Thus, it may be proposed that the radical pathway is probably responsible for conversion of 3,5-DTBC to 3,5-DTBQ promoted by complexes of redox-innocent Zn(II) ion. The ligand-centered radical generation has further been verified by density functional theory calculation. |
| Databáze: | OpenAIRE |
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