Homodinuclear [Fe(III)−Fe(III)] and [Zn(II)−Zn(II)] complexes of a binucleating [N4O3] symmetrical ligand with purple acid phosphatase (PAP) and zinc phosphoesterase like activity

Abstract

The homodinuclear [Fe(III)–Fe(III)] (2) and [Zn(II)–Zn(II)] (3) complexes of binucleating [N4O3] symmetrical ligand (1) of the formulation, H3L (L = 2,6-bis{[(2-hydroxybenzyl)(2-pyridylmethyl)amino]methyl}-4-t-butylphenolate), display purple acid phosphatase (PAP) and zinc phosphoesterase like activity. For the two complexes, the spectrophotometric titration and the ESI-MS studies supported the existence of an equilibrium between a triaquated species, {L[(H2O)FeIII(μ-H2O)FeIII(H2O)]}3+ (2A) and {L[(H2O)ZnII(μ-H2O)ZnII(H2O)]}+ (3A), a diaquated and monohydroxo species, {L[(H2O)FeIII(μ-H2O)FeIII(OH)]}2+ (2B) and {L[(H2O)ZnII(μ-H2O)ZnII(OH)]} (3B), a monoaquated and dihydroxo species, {L[(H2O)FeIII(μ-OH)FeIII(OH)]}+ (2C) and {L[(H2O)ZnII(μ-OH)ZnII(OH)]}− (3C), and a trihydroxo species, {L[(HO)FeIII(μ-OH)FeIII(OH)]} (2D) and {L[(HO)ZnII(μ-OH)ZnII(OH)]}2− (3D), depending upon the pH of the solution. Of these, the active species namely, a monoaquated and dihydroxo species, {L[(H2O)FeIII(μ-OH)FeIII(OH)]}+ (2C) and {L[(H2O)ZnII(μ-OH)ZnII(OH)]}− (3C), hydrolyzed an activated substrate bis(2,4-dinitrophenyl)phosphate at the pH range of 5.5–10.5, displaying Michealis–Menton kinetics. Significantly enough, the catalyst-substrate adduct of the type {L[FeIII(μ-OH)(μ-RPO4)FeIII]} (2F) has been detected by ESI-MS for the dinuclear [Fe(III)–Fe(III)] complex (2).