Abstract
A dinickel(II) complex of the ligand 1,3-bis(bis(pyridin-2-ylmethyl)amino)propan-2-ol (HL1) has been prepared and characterized to generate a functional model for nickel(II) phosphoesterase enzymes. The complex, [Ni2(L1)(μ-OAc)(H2O)2](ClO4)2·H2O, was characterized by microanalysis, X-ray crystallography, UV-visible, and IR absorption spectroscopy and solid state magnetic susceptibility measurements. Susceptibility studies show that the complex is antiferromagnetically coupled with the best fit parameters J = −27.4 cm−1, g = 2.29, D = 28.4 cm−1, comparable to corresponding values measured for the analogous dicobalt(II) complex [Co2(L1)(μ-OAc)](ClO4)2·0.5 H2O (J = −14.9 cm−1 and g = 2.16). Catalytic measurements with the diNi(II) complex using the substrate bis(2,4-dinitrophenyl)phosphate (BDNPP) demonstrated activity toward hydrolysis of the phosphoester substrate with Km ~10 mM, and kcat ~0.025 s−1. The combination of structural and catalytic studies suggests that the likely mechanism involves a nucleophilic attack on the substrate by a terminal nucleophilic hydroxido moiety.
Highlights
Our understanding of the bioinorganic significance of nickel can be traced to the discovery that the specific activity of the soluble jack bean urease, after partial EDTA-promoted inactivation, was a linear function of the nickel content, consistent with the presence of two nickel(II) ions per subunit of the pure enzyme (Dixon et al, 1980; Blakeley et al, 1982; Blakeley and Zerner, 1984)
We have reported previously a diZn(II) complex with L1− as a functional model for zinc(II) phosphoesterase enzymes (Mendes et al, 2016)
In this work the dinuclear nickel complex [Ni2(L1)(μOAc)(H2O)2](ClO4)2.H2O was synthesized from a reaction of HL1 with two equivalents of nickel(II) acetate in methanol
Summary
Our understanding of the bioinorganic significance of nickel can be traced to the discovery that the specific activity of the soluble jack bean urease, after partial EDTA-promoted inactivation, was a linear function of the nickel content, consistent with the presence of two nickel(II) ions per subunit of the pure enzyme (Dixon et al, 1980; Blakeley et al, 1982; Blakeley and Zerner, 1984) Previous to this discovery the importance of metal ions in general for the activity of urease was known, the specific requirement for Ni(II) ions was not (Jacoby, 1933; Shaw, 1954; Shaw and Raval, 1961; Spears et al, 1977). This flexibility of PAPs with respect to their use of metal ions may be a reflection of their dual function as a phosphatase and peroxidase; in its di-Fe(III) form PAP is and reversibly reduced to the heterovalent Fe(III)Fe(II) form (redox potential ∼340 mV), a process that allows the enzyme to act as a Fenton catalyst (Sibille et al, 1987; Bernhardt et al, 2004)
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