Phenoxazinone synthase and antimicrobial activity by a bis(1,3-diamino-2-propanolate) cobalt(III) complex

Abstract

In this work, we have synthesised and structurally characterized a mononuclear cobalt(III) complex, $$[\hbox {Co(2-O-pn)}_{2}]\hbox {Cl}^{.} \hbox {2H}_{2} \hbox {O}$$ (1), (2-O-pn = 1,3-diamino-2-propanolate). From the X-ray structure of the cobalt complex, it is revealed that Co(III) ion in 1 adopts an octahedral geometry and crystallizes in the monoclinic system with C2 / c space group. The lattice aqua molecule in combination with chloride ion in 1 forms a water-chloride cluster, $$(\hbox {H}_{2} \hbox {O})_{2}{}^{\cdots } \, \hbox {(Cl)}_{2}$$ through strong H-bonding interaction mediated via cobalt(III) complex in a unique binding motif. This cobalt(III) complex has been tested as an effective catalytic system towards the oxidative coupling of 2-aminophenol (2-AP) in the MeCN medium. In situ mass spectral analysis confirms that 2-AP forms an adduct with cobalt ion and the course of catalysis proceeds through catalyst-substrate binding followed by oxidative coupling of 2-AP with iminobenzoquinone. This cobalt(III) catalyst affords exclusively aminophenoxazinone species with a significant turnover number, $$k_{\mathrm{cat}}: \, 6.37 \times 10^{2} \, \hbox {h}^{-1}$$ in the MeCN medium. This cobalt(III) complex is able to screen out the growth of some bacteria and fungi species. Quantum chemical calculations employing density functional theory is used to model structural parameters and spectroscopic behaviour. The theoretical findings corroborate well with the experimental results. SYNOPSIS A mononuclear cobalt(III) complex exhibits significant catalytic efficacy towards oxidative coupling of 2-aminphenol (2-AP) in MeCN medium and predominantly produces aminophenoxazinone species with a significant turn over number, $$k_{\mathrm{cat}}: \, 6.37 \times 10^{2} \, \hbox {h}^{-1}$$ in presence of molecular oxygen.