Abstract
Heterodinuclear mixed valence [Zn(II)−Fe(III)] and the homodinuclear [Zn(II)−Zn(II)] and [Ni(II)−Ni(II)] complexes of a bicompartmental ligand containing a bridging phenoxy as a O−donor and four pyridyl moieties and two amine moieties as the N−donors exhibit phosphoester hydrolysis activity similar to the hydrolase family of enzymes. While the heterodinuclear [Zn(II)−Fe(III)] (2) complex was obtained by the sequential addition of Fe(NO3)3∙9H2O and Zn(OAc)2∙2H2O to the ligand 2,6‑bis{[bis(2‑pyridylmethyl)amino]methyl}‑4‑t‑butylphenol (HL) (1) in moderate yield of 37%, the homodinuclear [Zn(II)−Zn(II)] (3) and [Ni(II)−Ni(II)] (4) complexes were obtained by the direct reaction of the ligand (1) with Zn(OAc)2∙2H2O and Ni(OAc)2∙2H2O respectively, in good to moderate yields (43–63%). Based on the spectrophotometric titration and the mass spectrometry studies, a monoaquated and dihydroxo species 2C, 3C and 4C has been identified as the catalytically active species responsible for the phosphodiester hydrolysis of the bis(2,4 − dinitrophenyl)phosphate (2,4 − BDNPP) substrate in the pH range 5.5–10.5. The kinetic studies further revealed that the homodinuclear [Ni(II)−Ni(II)] complexes (4) (kcat = 1.26 × 10−2 s−1) is more active by 39 times than the homodinuclear [Zn(II)−Zn(II)] complexes (3) (kcat = 3.20 × 10−4 s−1) and 27 times more active than the heterodinuclear [Zn(II)−Fe(III)] complex (2) (kcat = 4.62 × 10−4 s−1) in the phosphodiester hydrolysis activity. Significantly enough, the catalyst−substrate adduct species (2E, 2F and 3F) containing a metal bound bis(2,4‑dinitrophenyl)phosphate has been detected by mass spectrometry for the first time.
A heterodinuclear mixed valence zinc‑iron and two homodinuclear zinc‑zinc and nickel‑nickel type complexes supported over a symmetrical nitrogen and oxygen donors bearing ligand serve as small molecule functional mimics of the hydrolase family of enzymes. [Display omitted]
•Hetero and homodinuclear complexes of Fe, Zn and Ni act as functional mimics of hydrolases.•Mass spectrometric detection of catalytically active monoaquated and dihydroxo species.•Mass spectrometric detection of catalyst-substrate species in phosphodiester hydrolysis.