pyrophosphate and 2-2--azino-di-(3-ethylbenzothiazoline)-6-sulfonic-acid

In this study, it was, interestingly, found that 2,2'-azino-bis(3-ethylbenzothiazoline)-6-sulfonate (ABTS), a widely used electron shuttle, could greatly accelerate the oxidation of substituted phenols by potassium permanganate (Mn(VII)) in aqueous solutions at pH 5-9. This was attributed to the fact that these substituted phenols could be readily oxidized by the stable radical cation (ABTS(•+)), which was quickly produced from the oxidation of ABTS by Mn(VII). The reaction of Mn(VII) with ABTS exhibited second-order kinetics, with stoichiometries of ∼5:1 at pH 5-6 and ∼3:1 at pH 7-9, and the rate constants varied negligibly from pH 5 to 9 (k = (9.44 ± 0.21) × 10(4) M(-1) s(-1)). Comparatively, the reaction of ABTS(•+) with phenol showed biphasic kinetics. The second-order rate constants for the reactions of ABTS(•+) with substituted phenols obtained in the initial phase were strongly affected by pH, and they were several orders of magnitude higher than those for the reactions of Mn(VII) with substituted phenols at each pH. Good Hammett-type correlations were found for the reactions of ABTS(•+) with undissociated (log(k) = 2.82-4.31σ) and dissociated phenols (log(k) = 7.29-5.90σ). The stoichiometries of (2.2 ± 0.06):1 (ABTS(•+) in excess) and (1.38 ± 0.18):1 (phenol in excess) were achieved in the reaction of ABTS(•+) with phenol, but they exhibited no pH dependency.

Topics: Benzothiazoles; Diphosphates; Electrons; Hydrogen-Ion Concentration; Kinetics; Manganese; Manganese Compounds; Oxidants; Oxidation-Reduction; Oxides; Phenols; Solutions; Sulfonic Acids; Thermodynamics; Water

The evaluation of pyrophosphatase (PPase) activity plays an important role in diagnosing diseases and understanding the function of PPase in the related biological events. In this work, an inhibition effect of pyrophosphate (PPi) on Cu(2+)-catalyzed H2O2-mediated oxidation of 2,2-azinobis(3-ethylbenzothiazoline)-6-sulfonic acid (ABTS) was observed. We utilize this inhibition effect to develop a convenient label free visual method for PPase activity detection. A hydroxyl radical could be generated from a Cu(2+)-based Fenton-like reaction, and then reacted with ABTS to produce colored ABTS˙(+). The strong complexation between PPi and Cu(2+) disturbed this Cu(2+)-catalyzed ABTS-H2O2 reaction probably due to changing redox potentials of Cu(2+) towards H2O2. The PPase-catalyzed hydrolysis of PPi into Pi prohibited the complexation, resulting in the recovery of catalytic capability of Cu(2+). As a result, the solution color changed from colorless to green with a remarkable increase of absorbance. Compared with the traditional PPase assays, the developed visual assay is cost-effective and easy to implement. And a high sensitivity for PPase with a detection limit of 0.027 U mL(-1) was achieved. Moreover, the proposed colorimetric strategy was also applied to evaluate PPase inhibition and exhibited a good assay performance in complex biological samples.

Topics: Benzothiazoles; Colorimetry; Copper; Diphosphates; Hydrogen Peroxide; Oxidation-Reduction; Pyrophosphatases; Sensitivity and Specificity; Sulfonic Acids