Issue 18, 2020

Synthesis of Mn3O4 nanozymes from structurally characterized phenoxazinone synthase models based on manganese(iii) Schiff base complexes

Abstract

Three mononuclear and one hexanuclear manganese(III) complexes, [Mn(L)(H2O)2]·Cl (1), [Mn(L)(H2O)2]·Br (2), [Mn(L)(H2O)2]·NO3 (3), and [Mn6(L)6(NCS)6] (4), have been synthesized using a Schiff-base ligand, namely (E)-2-((3-(2-hydroxyethylamino)propylimino)methyl)phenol (H2L), and structurally characterized by the usual physicochemical techniques such as UV-Vis, FT-IR, ESI-MS, EPR and single crystal XRD. The structure of complex 4 is unique among all four complexes as the sixth coordination position of manganese is fulfilled by the oxygen atom of a neighbouring unit by covalent interaction. The phenoxazinone synthase like activity of all four complexes has been thoroughly investigated using three different substrates, o-aminophenol (OAP), 2-amino-4-methylphenol (MAP) and 3-amino-4-hydroxybenzoic acid (CAP). All complexes were found to be active towards catalysis and complex 4 showed the highest activity. The EPR study reveals that the oxidative dimerization of the substrates occurred through metal centered redox participation rather than a radical formation pathway. The experimental observations have been supported by DFT calculations to put forward the most probable mechanistic pathways operating in the catalytic cycle. Moreover, Mn3O4 nanoparticles (NPs) having two different morphologies have been synthesized using complexes 1 and complex 4 simply by calcination, respectively, with the aim to prepare nanozymes. These two synthesized NPs were also able to show phenoxazinone synthase like activity and thus complexes 1 and 4 can be claimed as precursors of nanozymes.

Graphical abstract: Synthesis of Mn3O4 nanozymes from structurally characterized phenoxazinone synthase models based on manganese(iii) Schiff base complexes

Supplementary files

Article information

Article type
Paper
Submitted
31 Jan 2020
Accepted
03 Apr 2020
First published
04 Apr 2020

Dalton Trans., 2020,49, 5999-6011

Synthesis of Mn3O4 nanozymes from structurally characterized phenoxazinone synthase models based on manganese(III) Schiff base complexes

A. Mandal, S. Dasgupta, A. Adhikary, D. Samanta, E. Zangrando and D. Das, Dalton Trans., 2020, 49, 5999 DOI: 10.1039/D0DT00355G

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