Phosphatase-mimicking activity of a unique penta-nuclear zinc(ii) complex with a reduced Schiff base ligand: assessment of its ability to sense nitroaromatics

Abstract

A unique penta-nuclear zinc(II) complex, [(μ_1,1-N₃)₂{(N₃)Zn(L)Zn}₂Zn(L)] {H₂L= 2,2′-[(1-methyl-1,2-ethanediyl)bis(iminomethylene)]bis[6-methoxyphenol]}, has been synthesized and characterized. X-ray crystallographic analysis has confirmed its structure. The complex has shown good phosphatase-mimicking activity {k_cat ∼ 398 h⁻¹ at 298 K}, evaluated spectrophotometrically by monitoring the increase in absorbance at ∼425 nm, indicating gradual release of p-nitrophenolate by the hydrolysis of 4-nitrophenylphosphate ester with time, when 4-NPP (disodium 4-nitrophenylphosphate hexahydrate) has been used as a substrate. The complex behaves as a sensor for the detection of nitroaromatics in DMF solution via turn-off fluorescence response. The solution phase sensing mechanism has been studied and a strong quenching efficiency has been found with a quenching constant (K_SV) of 6.497 × 10⁴ M⁻¹ for 3-methyl-4-nitrobenzoic acid.