Design, synthesis, structural, spectral, and redox properties and phenoxazinone synthase activity of tripodal pentacoordinate Mn(ii) complexes with impressive turnover numbers

Kumbhakar, Sadananda and Giri, Bishnubasu and Muley, Arabinda and Karumban, Kalai Selvan and Maji, Somnath (2021) Design, synthesis, structural, spectral, and redox properties and phenoxazinone synthase activity of tripodal pentacoordinate Mn(ii) complexes with impressive turnover numbers. Dalton Transactions, 50 (45). pp. 16601-16612. ISSN 1477-9226

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Catechol oxidase (CO) and phenoxazinone synthase (PHS) are two enzymes of immense significance due to their capability to oxidize catechols and o-aminophenols to o-quinones and phenoxazinones, respectively. In this connection two mononuclear manganese complexes with the molecular framework [MnII(Ln)Cl]Cl {L1: tris((1H-benzo[d]imidazol-2-yl)methyl)amine; n = 1 and L2: tris(N-methylbenzimidazol-2-ylmethyl)amine; n = 2} have been designed to be potential catalysts for OAPH (o-aminophenol) oxidation. Both the ligands and their corresponding metal complexes have been successfully synthesized and thoroughly characterized by different spectroscopic and analytical techniques such as FT-IR, 1H NMR, UV-vis spectroscopy, EPR spectroscopy and ESI mass spectroscopy. The molecular structures of [MnII(L1)Cl]Cl (1) and [MnII(L2)Cl]Cl (2) have been revealed by a single-crystal X-ray diffraction study. The spectral properties and redox behaviour of both the complexes were examined. Under ambient conditions, 1 and 2 show excellent phenoxazinone synthase activity as both are very susceptible to oxidize o-aminophenol to phenoxazinone. The kinetic parameters for both complexes have been determined by analyzing the experimental spectroscopic data. The turnover numbers (kcat value) of these two complexes are extremely high, 440 h-1 and 234 h-1 for 1 and 2, respectively. The present report offers a thorough overview of information involving the role of the metal ions and their extent of phenoxazinone synthase mimicking activity. The oxidation of o-aminophenol to 2-amino-3H-phenoxazine-3-one (APX) by catalytic oxidation of oxygen (O2) by the reaction with transition metal complexes has been an important study for the last few decades. The current study evidently showed better performance of our synthesized Mn(ii) complexes than all the predecessors. The plausible mechanism has been reiterated based on the experimental data via ESI-MS spectra and considering the concepts from the previously reported mechanisms involved in the formation of hydrogen peroxide (H2O2) as an intermediate substrate is fairly indicating the involvement of molecular oxygen in the catalytic cycle. © 2021 The Royal Society of Chemistry.

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IITH Creators:
IITH CreatorsORCiD
Maji, Somnath
Item Type: Article
Additional Information: Financial support received from the Science and Engineering Research Board (SERB), Department of Science and Technology, India: project no. ECR/2016/000382 (fellowship to S. K.), the Council of Scientific and Industrial Research (CSIR) (fellowship to B. G., A. M., and K. S.) and the Indian Institute of Technology Hyderabad is gratefully acknowledged. We would also like to thank Mr Hemant Rawat for the measurement of a single crystal of complex 2. Special thanks to Dr Shaikh M. Mobin for helpful crystallographic discussion.
Uncontrolled Keywords: Catechol oxidase; Design synthesis; Manganese complexes; O aminophenols; O-quinones; Redox property; Spectral properties; Synthases; Synthesised; Turnover number
Subjects: Chemistry
Divisions: Department of Chemistry
Depositing User: . LibTrainee 2021
Date Deposited: 17 Aug 2022 13:59
Last Modified: 17 Aug 2022 13:59
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