The active site of the purple acid phosphatase enzyme has been successfully modeled by a series of hetero-dinuclear M(II)–Fe(III) [M = Zn, Ni, Co, and Cu] type complexes of an unsymmetrical [N 6 O] ligand that contained a bridging phenoxide moiety and one imidazoyl and three pyridyl moieties as the terminal N-binding sites. In particular, the hetero-dinuclear complexes, {L[M II (μ-OAc) 2 Fe III ]}(ClO 4 ) 2 [M = Zn ( 3a ), Ni ( 3b ), Co ( 4a ), and Cu ( 4b )], were obtained directly from the phenoxy-bridged ligand (HL), namely 2-{[bis(2-methylpyridyl)amino]methyl}-6-{[((1-methylimidazol-2-yl)methyl)(2-pyridylmethyl)amino]methyl}-4- t -butylphenol ( 2 ), upon sequential addition of Fe(ClO 4 ) 3 · X H 2 O and M(ClO 4 ) 2 ·6H 2 O (M = Zn and Ni) or M(OAc) 2 · X H 2 O (M = Co and Cu), in a low-to-moderate (ca. 32–53%) yield. The temperature-dependent magnetic susceptibility measurements indicated weak antiferromagnetic coupling interactions occurring between the two metal centers in their high-spin states. All of the 3 ( a–b ) and 4 ( a–b ) complexes successfully carried out the hydrolysis of the bis(2,4-dinitrophenyl)phosphate (2,4-BDNPP) substrate in a mixed CH 3 CN/H 2 O (v/v 1:1) medium in the pH range of 5.5–10.5 at room temperature, thereby mimicking the functional activity of the native enzyme. The spectrophotometric titration suggested a monoaquated and dihydroxo species of the type {L[(H 2 O)M II (μ-OH)Fe III (OH)]} 2+ to be the catalytically active species for the phosphodiester hydrolysis reaction within the pH range of ca. 5.80–7.15. Last, the kinetic studies on the hydrolysis of the model substrate, 2,4-BDNPP, divulge a Michaelis–Menten-type behavior for all complexes.

No abstract

Biaryl scaffolding ligands form dicobalt clusters, which serve as efficient catalysts in enaminone synthesis under ambient conditions.

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(NO)∙9HO and Zn(OAc)∙2HO 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)∙2HO and Ni(OAc)∙2HO 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) (k = 1.26 × 10 s) is more active by 39 times than the homodinuclear [Zn(II)-Zn(II)] complexes (3) (k = 3.20 × 10 s) and 27 times more active than the heterodinuclear [Zn(II)-Fe(III)] complex (2) (k = 4.62 × 10 s) 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.

No abstract