An [Mn-2(bpmp)](3+) complex as an artificial peroxidase and its applications in colorimetric pyrophosphate sensing and cascade-type pyrophosphatase assay

Abstract

The development of artificial peroxidases has attracted great interest because of their applications in various fields such as the chemical industry and biosensing. In this study, 2,6-bis[(bis(2-pyridylmethyl) amino)-methyl]-4-methylphenol (H-bpmp) complexes with various transition metal ions have been investigated as artificial peroxidases. Among these metal complexes, the [Mn-2(bpmp)](3+) complex showed the highest peroxidase-like activity as determined by a colorimetric assay using 2,2'-azino-bis(3ethylbenzothiazoline-6-sulphonic acid) (ABTS) and H2O2. The peroxidase-like activity was inhibited by pyrophosphate (PPi), which blocked the active site of the [Mn-2(bpmp)](3+) complex. Based on this phenomenon, the ABTS/H2O2/[Mn-2(bpmp)](3+) system could be applied for the detection of PPi, which could be achieved selectively by visual observation with a detection limit of 130 nM. Moreover, the addition of pyrophosphatase (PPase) to the [Mn-2(bpmp)](3+) complex blocked by PPi resulted in the recovery of the peroxidase-like activity of the [Mn-2(bpmp)](3+) complex due to the hydrolysis of PPi. Hence, the enzyme cascade reaction of the PPase and [Mn-2(bpmp)](3+) complex allowed the real-time colorimetric assay of PPase.