Synthesis, Structure, and Physicochemical Properties of Dinuclear Ni^II Complexes as Highly Efficient Functional Models of Phosphohydrolases

Abstract

As metal ions are present in the catalytic sites of several enzymes, attention has been focused on the synthesis and characterization of metal complexes able to act as biomimetic functional and structural models for these systems. In this study, a novel dinuclear NiII complex was synthesized, [Ni2(L2)(OAc)2(CH3CN)]BPh4 (2) (HL2=2-[N-(2-(pyridyl-2-yl)ethyl)(1-methylimidazol-2-yl)amin omethyl]-4-methyl-6-[N-(2-(imidazol-4-yl)ethyl)amino methyl]phenol), employing a new unsymmetrical dinucleating ligand containing N,O-donor groups as a model for hydrolases. Complex 2 was characterized by a variety of techniques including: elemental analysis, infrared and UV-vis spectroscopies, molar conductivity, electrochemistry, potentiometric titration, magnetochemistry, and single-crystal X-ray diffractometry. The structural and magnetochemical data of 2 allow us to consider this complex as a structural model for the active site of the ureases, as previously reported for [Ni2(L1)(OAc)2(H2O)]ClO4.H2O (1) (HL1=2-[N-bis-(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N-(2-pyridylmethyl)aminomethyl] phenol). The characterization of complexes 1 and 2 (mainly by X-ray diffraction and potentiometric titration) led us to study their reactivities toward the hydrolysis of the substrate bis(2,4-dinitrophenyl)phosphate (2,4-BDNPP). These studies revealed that complexes 1 and 2 show the best catalytic activity reported so far, with acceleration rates 8.8x10(4) and 9.95x10(5) times faster, respectively, than the uncatalyzed hydrolysis of 2,4-BDNPP. Catalytic activity of 2 on 2,4-DNPP showed that the monoester is hydrolyzed 27 times slower than the 2,4-BDNPP diester under identical experimental conditions. Therefore, 1 and 2 can undoubtedly be considered highly efficient functional models of the phosphohydrolases.

Structural and Catalytic Characterization of a Heterovalent Mn(II)Mn(III) Complex That Mimics Purple Acid Phosphatases

“…19 Since a Mn(III)-bound hydroxide would be expected to be as reactive as a Fe(III)-bound one, the observed lower activity of the Mn(II)Mn(III) complex suggests the bridging hydroxide as the nucleophile (because of its poorer nucleophilicity 114,116,117 …”

Role of Electronegative Atom Present on Ligand Backbone and Substrate Binding Mode on Catecholase‐ and Phosphatase‐Like Activities of Dinuclear NiII Complexes: A Theoretical Support

“…The magnetic properties of 1 and 2 , in the form of χ M and χ M T (χ M is the susceptibility per dimeric unit) vs . T plots, are shown in Figure in a temperature range 3–300 K. The χ M T value at room temperature, 2.30 cm 3 K mol −1 (μ eff= 4.29 μ B ) for 1 and 2.33 emu K mol −1 (μ eff= 4.31 μ B ) for 2 , which are a little higher than the expected value of 2 emu K mol −1 (μ eff =4 μ B ) of two independent Ni II ions ( S =1 with g=2.0), which agrees with the value found for similar compounds,, which is mainly due to the orbital contribution of the Ni II ions. When decreasing the temperature, the χ M T product decreases gradually to a minimum at 70 K and then rises to a maximum of 2.29 emu K mol −1 at 8 K and final decrease to 2.10 emu K mol −1 at 3 K for 1 , suggesting the presence of a ferromagnetic interaction between the pair of nickel(II) ions.…”

Synthesis, crystal structures, and catalytic hydrolysis activities of four dinuclear complexes with 1,4,7,10-tetraazacyclododecane and succinate ligands

“…Very recently, Greatti reported a novel dinuclear complex with the best catalytic activity reported so far, with acceleration rates *10 5 times faster than the uncatalyzed hydrolysis of BDNPP [37]. Some other complexes also showed a fast hydrolysis rate of BDNPP [27,38,39].…”