A novel asymmetric di-Ni(ii) system as a highly efficient functional model for phosphodiesterase: synthesis, structures, physicochemical properties and catalytic kinetics

Abstract

A novel asymmetric phenol-based 'end-off' dinucleating ligand 2-{[(2-piperidylmethyl)amino]methyl}-4-bromo-6-[(1-methylhomopiperazine-4-yl)methyl]phenol (HL) and three dinuclear nickel(II) complexes, [Ni₂L(μ-OH)] (ClO₄)₂ (1), [Ni₂L(DNBA)₂(CH₃CN)₂]BPh₄ (2) and [Ni₂L(BPP)₂(CH₃CN)₂]BPh₄ (3) have been synthesized and characterized by a variety of techniques including: NMR, infrared and UV-vis spectroscopies, mass spectrometry, elemental analysis, molar conductivity, thermal analysis, magnetochemistry and single-crystal X-ray diffractometry. The UV-vis spectrum of complex 1 exhibits a strong peak at 510 nm, a characteristic absorption of a d-d transition of the square-planar four-coordinated Ni(II) center. Utilizing this feature, the stepwise formation of mono- and dinickel centers in solution can be monitored. Phosphodiesterase activity of a dinuclear Ni(II) system (complex 1), formed in situ by a 2 : 1 mixture of Ni(2+) ions and the ligand HL, was investigated using bis(4-nitrophenyl)phosphate (BNPP) as the substrate. The pH dependence of the BNPP cleavage in water-ethanol (1 : 1, v/v) reveals a bell-shaped pH-k(obs) profile with an optimum at about pH 8.3 which is parallel to the formation of the dinuclear species [Ni₂L(μ-OH)](2+), according to the increase of the peak at 510 nm in the UV-vis absorption spectrum . These studies reveal that the di-Ni(II) system shows the highest catalytic activity reported so far, with an acceleration rate 1.28 × 10⁷ times faster than the uncatalyzed reaction. The bridging hydroxyl group in [Ni₂L(μ-OH)](2+) is responsible for the hydrolysis reaction. The possible mechanism for the BNPP cleavage promoted by di-Ni(II) system is proposed on the basis of kinetic and spectral analyses. This study provides a less common example of the asymmetric phosphodiesterase model, which is like the active sites of most native metallohydrolases.

Heterodinuclear Zn(II)−Fe(III) and Homodinuclear M(II)−M(II) [M = Zn and Ni] complexes of a Bicompartmental [N 6 O] ligand as synthetic mimics of the hydrolase family of enzymes

“…The confirmation of the same came from the variable temperature χ M T plot that showed a decrease of χ M T value with temperature due to the antiferromagnetic coupling between the two Ni(II) center (Figure 2). The A C C E P T E D M A N U S C R I P T 19 curve fitting analysis using the PHI software gave g value of g Ni = 2.00 and an exchange coupling J = −1.05 cm -1 comparable to the earlier observed ranges of g Ni (2.17−2.18) and the exchange coupling in the range J [−(0.8−3.8) cm -1 ] for the related dinuclear Ni(II)−Ni(II)complexes known in the literature[87,88,100,113].…”

“…types having a variety of binucleating metal bridging sites namely {[N 3 O], [N 3 O]} [41-43, 58-61], {[N 3 O], [N 2 O 2 ]} [55-57, 62-70], {[N 3 O], [NO 3 ]} [71, 72], {[N 3 O], [N 2 O]} [73], {[N 2 O 2 ], [NO 3 ]} [52] {[N 2 O 2 ], [N 2 O]} [31, 74-79], {[N 2 O 2 ], [N 2 O 2 ]} [79-85], {[N 2 O], [N 2 O]}[86][87][88][89] and the {[NO 2 ], [N 3 O]}…”

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

“…Thus, the general rate of spontaneous hydrolysis was not separately determined. Kinetic data for phosphatase like activities of previously reported dinuclear nickel complexes,,,,,,, are presented in Table . Comparing the Tables and , it is evident that both the complexes 1 and 2 belong to high catalytically active group towards hydrolysis of 4‐NPP and the activity is higher for 1 .…”

Phosphodiester Cleavage Promoted by an Asymmetric Di­nuclear Zinc Complex: Synthesis, Structure, and Catalytic ­Activity

“…The reciprocal of the Michaelis‐Menten constant could be treated as the substrate binding constant, that is, K b = 1/ K M = 138.5 M –1 . The low K b is fit for the observations that BNPP is a weak ligand for Zn 2 L 28,29. At pH 7.9 ([OH – ] = 6.31 × 10 –7 M ]) and 25 °C, the first‐order rate constant ( k = k OH [OH – ]) of automatic hydrolysis of BNPP is calculated to be 3.66 × 10 –12 s –1 with k OH = 5.8 × 10 –6 M –1 · s –1 for BNPP ( V auto = k OH [BNPP][OH – ]) 30.…”